Interview Question for active directory and exchange
<>1. What is PCI bus (Peripheral Component Interconnect Bus).
Short for Peripheral Component Interconnect, a local bus standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus. PCI is also used on newer versions of the Macintosh computer.
PCI is a 64-bit bus, though it is usually implemented as a 32-bit bus. It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps.
<>2. What is cache (Internal & External ) memory.
Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.
Cache memory is sometimes described in levels of closeness and accessibility to the microprocessor. An L1 cache is on the same chip as the microprocessor. (For example, the PowerPC 601 processor has a 32 kilobyte level-1 cache built into its chip.) L2 is usually a separate static RAM (SRAM) chip. The main RAM is usually a dynamic RAM (DRAM) chip.
In addition to cache memory, one can think of RAM itself as a cache of memory for hard disk storage since all of RAM's contents come from the hard disk initially when you turn your computer on and load the operating system (you are loading it into RAM) and later as you start new applications and access new data. RAM can also contain a special area called a disk cache that contains the data most recently read in from the hard disk.
Pronounced cash, a special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching.
A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.
Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.
Cache memory is sometimes described in levels of closeness and accessibility to the microprocessor. An L1 cache is on the same chip as the microprocessor. (For example, the PowerPC 601 processor has a 32 kilobyte level-1 cache built into its chip.) L2 is usually a separate static RAM (SRAM) chip. The main RAM is usually a dynamic RAM (DRAM) chip.
In addition to cache memory, one can think of RAM itself as a cache of memory for hard disk storage since all of RAM's contents come from the hard disk initially when you turn your computer on and load the operating system (you are loading it into RAM) and later as you start new applications and access new data. RAM can also contain a special area called a disk cache that contains the data most recently read in from the hard disk.
<>3. What type of modems are there.
(mō´dem) (n.) Short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.
Fortunately, there is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems.
<>4. What is RAID and its types and mirroring.
(rād) Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.
There are number of different RAID levels:
· Level 0 -- Striped Disk Array without Fault Tolerance: Provides data striping (spreading out blocks of each file across multiple disk drives) but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost.
· Level 1 -- Mirroring and Duplexing: Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks.
· Level 2 -- Error-Correcting Coding: Not a typical implementation and rarely used, Level 2 stripes data at the bit level rather than the block level.
· Level 3 -- Bit-Interleaved Parity: Provides byte-level striping with a dedicated parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely used.
· Level 4 -- Dedicated Parity Drive: A commonly used implementation of RAID, Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails, the parity data is used to create a replacement disk. A disadvantage to Level 4 is that the parity disk can create write bottlenecks.
· Level 5 -- Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.
· Level 6 -- Independent Data Disks with Double Parity: Provides block-level striping with parity data distributed across all disks.
· Level 0+1 – A Mirror of Stripes: Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. Used for both replicating and sharing data among disks.
· Level 10 – A Stripe of Mirrors: Not one of the original RAID levels, multiple RAID 1 mirrors are created, and a RAID 0 stripe is created over these.
· Level 7: A trademark of Storage Computer Corporation that adds caching to Levels 3 or 4.
· RAID S: EMC Corporation's proprietary striped pairty RAID system used in its Symmetrix storage systems.
Mirroring
Mirroring involves having two copies of the same data on separate hard drives or drive arrays. So basically the data is effectively mirrored on another drive. The system basically writes data simultaneously to both hard drives. This is one of the two data redundancy techniques used in RAID to protect from data loss. The benefit is that when one hard drive or array fails, the system can still continue to operate since there are two copies of data. Downtime is minimal and data recovery is relatively simple. All you need to do is rebuild the data from the good copy.
The following diagram illustrates how mirroring actually works. Of course, this is a simplified diagram. A, B, and C are separate files that reside on each disk. Disk 1 and 2 in this diagram don't necessarily have to be disks themselves. They can be arrays of drives. The main thing to remember here is that the RAID controller writes the same data blocks to each mirrored drive. Each drive or array has the same information in it. You can even add another level of complexity by introducing striping, which will be discussed shortly. I'm not going to get into what striping is now if you're not familiar with it, but just know it increases performance. If you have one striped array, you can mirror the array at the same time on a second striped array. It can get very complicated. To set up mirroring the number of drives will have to be in the power of 2 for obvious reasons.
The drawback here is that both drives are tied up during the writing process which limits parallelism and can hurt performance. In contrast, mirroring has a performance increase when dealing with reads. A good RAID controller will only read from one of the drives since the data on both are the same. While the other is used to read, the free drive can be used for other requests. This increases parallelism, which is pretty much the concept behind the performance increase of RAID.
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Mirroring may seem like a good solution to ensure the safety of data. However, the trade off here is the cost and wasted space involved with having two copies of the same data. You will need twice as much storage space to mirror the data. It can be cost effective for some applications where downtime can mean the downfall of a company or even loss of human life. Most of the time, however, it might not be worth it. Data might not be that critical to warrant spending twice as much on storage. The alternative to mirroring is parity, which is what the next section deals with.
<>5. How motherboard communicate with OS (through I/O port & IRQS)
An IRQ (Interrupt ReQuest) is a physical connection on the motherboard through which a piece of hardware communicates with the CPU and the OS; the CPU responds through an I/O (input/output) memory address. The so-called Standard IRQ assignments date back to the early days of DOS and Windows 3.x.
In the bad old days, IRQs had to be assigned manually, either by means of physical switches, jumpers, or with software. Even now, you may occasionally have to assign an IRQ manually.
<>6. Difference between FAT16, Fat32 & NTFS
FAT
File Allocation Table. A disc filing system used by Windows to establish the 'layout' of your hard drive. There are two different types of FAT: FAT16 and FAT32, differentiated by the fact that FAT16 is 16-bit and FAT32 is 32-bit. In essence, FAT16 gives faster disc access, while FAT32 delivers more space due to the smaller minimum data cluster size.
<>7. Tell something on TCPIP / OSI Model (ISO).
Summary: TCP and IP were developed by a Department of Defense (DOD) research project to connect a number different networks designed by different vendors into a network of networks (the "Internet"). It was initially successful because it delivered a few basic services that everyone needs (file transfer, electronic mail, remote logon) across a very large number of client and server systems. Several computers in a small department can use TCP/IP (along with other protocols) on a single LAN. The IP component provides routing from the department to the enterprise network, then to regional networks, and finally to the global Internet. On the battlefield a communications network will sustain damage, so the DOD designed TCP/IP to be robust and automatically recover from any node or phone line failure. This design allows the construction of very large networks with less central management. However, because of the automatic recovery, network problems can go undiagnosed and uncorrected for long periods of time.
As with all other communications protocol, TCP/IP is composed of layers:
- IP - is responsible for moving packet of data from node to node. IP forwards each packet based on a four byte destination address (the IP number). The Internet authorities assign ranges of numbers to different organizations. The organizations assign groups of their numbers to departments. IP operates on gateway machines that move data from department to organization to region and then around the world.
- TCP - is responsible for verifying the correct delivery of data from client to server. Data can be lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger retransmission until the data is correctly and completely received.
- Sockets - is a name given to the package of subroutines that provide access to TCP/IP on most systems.
There are three levels of TCP/IP knowledge
- The IP address assigned to this personal computer
- The part of the IP address (the subnet mask) that distinguishes other machines on the same LAN (messages can be sent to them directly) from machines in other departments or elsewhere in the world (which are sent to a router machine)
- The IP address of the router machine that connects this LAN to the rest of the world.
<>8. What is the difference between switch and Hub.
A hub is a fairly simple device that connects the computers. If we use the example of a phone system, it is like a constant conferance call. Every one can talk and listen to every one else, and if I speak to Jack, Jerry can here what I say, even if he does not care about what I am talking about. Everyone must take turns speaking.
With a switch however, things are more controled and it is more like the way the phone works most of the time. If you want to talk to someone, you dial their number, and if they are not screening their calls (to avoid you...) they answer and you can talk.
The switch keeps track of the MAC addresses of all the computers that are connected to it and when one computer wants to talk to another, the switch transfers the data between the two. I think the switch also allows other computers to also talk to each other at the same time.
While most people may never know the difference, it is always better to have a switch than a hub, and for some environsments where there is a
Gateway: Connects two different data protocols. A cable modem or DSL modem are gateways. In the cable modem example, the coax cable is converted to a CAT5 ethernet cable, and a DSL modem converts a telephone cable to CAT5
Routers: Routers connect two different subnets together, allowing the ability for different networks under different domains to talk. A network with a 255.255.255.0 subnet can talk to a 255.255.254 subnet via the router.
Hubs: Split the network connection x amount of ways. For example, a 20 port hub will literally switch one connection 20 ways. The problem? Packet collisions. There are revisions to fix this as set forth in the IEEE 802.3 standard
Switches: Smart hubs with memory, processors, and little operating systems. Switches recognize what device is broadcasting what. If a computer makes a request, say an internet page, the switch will grab the page and send it to the proper computer, not all. Also, switches are MAC address oriented while routers, hubs, and gateways are all IP address based.
<>9. What is Domain
A domain in AD is nothing but logical grouping of objects like users, computers, printers, O.U.
Active Directory
A network service that identifies all resources on a network and makes them accessible to users and applications. Resources include e-mail addresses, computers, and peripheral devices such as printers. Ideally, the directory service should make the physical network topology and protocols transparent so that a user on a network can access any resource without knowing where or how it is physically connected.
There are a number of directory services that are used widely. Two of the most important ones are LDAP, which is used primarily for e-mail addresses, and Netware Directory Service (NDS), which is used on Novell Netware networks. Virtually all directory services are based on the X.500 ITU standard, although the standard is so large and complex that no vendor complies with it fully.
Directory SERVICE IN NT
A directory service is an important part of a distributed computing environment that provides a way to locate and identify the users and resources available in the system. In its simplest form, directory services are like the white pages of a telephone book: Using specific input (a person's name), a user can receive specific output (a person's address and telephone number). Directory services also provide the functionality of the yellow pages-using general input (that is, where are the printers?), a user can receive a browsable listing of printer resources.
Windows NT Directory Service in version 4.0 accommodates a larger number of objects. Previously, the recommended maximum number of trusted domains was 128. In Windows NT Server 4.0, the Local Security Authority component has been enhanced to allow a greater number of trusted domains and to allow that number to scale with server memory.
<>10.What do you know about ADC
Active Directory Concepts
Active Directory has several components that work together to provide a complete directory service. They are as under :
Objects and Attributes : In ADS every component is called as Objects and every objects as some Attributes. Eg. users, computer, printers are called as objects and properties related to it is called as Attributes
Class : A Class is nothing but a container or a object containing sub objects like
Schema : Schema in nothing but a structure which define what objects and their attributes can be stored in ADS. When a domain is setup it contains a default schema know as DIT (Directory Information Tree). There are over 140 predefines classes and over 840 attributes stored in DIT. SCHMMGMT.MSC is used to view the schema of ADS
Domains : A domain in AD is nothing but logical grouping of objects like users, computers, printers, O.U.
Trees : They are logical grouping of Domains and Sub-Domains under a single hiraracery.
Organisation Unit : It is a sub-division of domain into multiple logical classes by administration for easy administration and management of objects in a container.
Domain Controller : DC is an object or Computer which runs Windows 2000 Serve Operating Systems and which maintains a copy of AD. In a domain we can have multiple DCs according to our requirement.
Global Catalog : GC is called as index file which helps to find objects in a large ADS. It is maintained by DC. When a users logs on the a machine the GC searches for object match and send the object query to the specific domain.
<>11.Explain DNS, WINS DHCP.
TCP/IP
Transmission Control Protocol/Internet Protocol (TCP/IP) is the most popular protocol, and the basis for the Internet. Its routing capabilities provide maximum flexibility in an enterprise-wide network. On a TCP/IP network, you must provide IP addresses to clients. Clients may also require a naming service or a method for name resolution like DNS or WINS. Every computer on a TCP/IP network must have a unique computer name and IP address. The IP address (together with its related subnet mask) identifies both the host computer and the subnet to which it is attached. TCP/IP address composed of 32 bit IP address from range of 0.0.0.0. to 255.255.255.255.
DNS
The Domain Name System (DNS) is an Internet and TCP/IP standard name service. The DNS service enables client computers on your network to register and resolve DNS domain names to IP address.
DHCP
Dynamic Host Configuration Protocol (DHCP) is a TCP/IP standard for simplifying management of host IP configuration. The DHCP standard provides for the use of DHCP servers as a way to manage dynamic allocation of IP addresses and other related configuration details to DHCP-enabled clients on your network.
When you move a computer to a different subnet, the IP address must be changed. DHCP allows you to dynamically assign an IP address to a client from a DHCP server IP address database on your local network:
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WINS
Windows Internet Name Service (WINS) provides a dynamic replicated database service that can register and resolve NetBIOS names to IP addresses used on your network. Windows 2000 Server provides WINS, which enables the server computer to act as a NetBIOS name server and register and resolve names for WINS-enabled client computers on your network as described in the NetBIOS over TCP/IP standards.
<>12.How do you do trust relationship between 2 or domains in NT
Trust Relationships
A trust relationship is a link between two domains in which the trusting domain honors the logon authentication of the trusted domain. Active Directory supports two forms of trust relationships
Types of Trust
<>• <> Implicit two-way transitive trust
<>• <> Explicit one-way non-transitive trust
Implicit two-way transitive trust.
A relationship between parent and child domains within a tree and between the top-level domains in a forest. This is the default; trust relationships among domains in a tree are established and maintained implicitly (automatically). Transitive trust is a feature of the Kerberos authentication protocol, which provides the distributed authentication and authorization in Windows 2000.
Transitive trust between domains eliminates the management of interdomain trust accounts. Domains that are members of the same tree automatically participate in a transitive, bidirectional trust relationship with the parent domain. As a result, users in one domain can access resources to which they have been granted permission in all other domains in a tree.
Example
A Kerberos transitive trust simply means that if Domain A trusts Domain B, and Domain B trusts Domain C, then Domain A trusts Domain C. As a result, a domain joining a tree immediately has trust relationships established with every domain in the tree. These trust relationships make all objects in the domains of the tree available to all other domains in the tree.
Example of Trust Relationship
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Explicit one-way nontransitive trust.
A relationship between domains that are not part of the same tree. A nontransitive trust is bounded by the two domains in the trust relationship and does not flow to any other domains in the forest. In most cases, you must explicitly (manually) create nontransitive trusts. A one-way, nontransitive trust is shown where Domain C trusts Domain 1, so users in Domain 1 can access resources in Domain C. Explicit one-way nontransitive trusts are the only form of trust possible with
<>• <>A Windows 2000 domain and a Windows NT domain
<>• <>A Windows 2000 domain in one forest and a Windows 2000 domain in another forest.
<>• <>A Windows 2000 domain and an MIT Kerberos V5 realm, allowing a client in a Kerberos realm to authenticate to an Active Directory domain in order to access network resources in that domain
<>13.What is the use of host & lmhost file and what does it contain
HOST FILE
The short answer is that the Hosts file is like an address book. When you type an address like www.yahoo.com into your browser, the Hosts file is consulted to see if you have the IP address, or "telephone number," for that site. If you do, then your computer will "call it" and the site will open. If not, your computer will ask your ISP's (internet service provider) computer for the phone number before it can "call" that site. Most of the time, you do not have addresses in your "address book," because you have not put any there. Therefore, most of the time your computer asks for the IP address from your ISP to find sites.
If you put ad server names into your Hosts file with your own computer's IP address, your computer will never be able to contact the ad server. It will try to, but it will be simply calling itself and get a "busy signal" of sorts. Your computer will then give up calling the ad server and no ads will be loaded, nor will any tracking take place. Your choices for blocking sites are not just limited to blocking ad servers. You may block sites that serve advertisements, sites that serve objectionable content, or any other site that you choose to block.
Try to locate any existing hosts file on your computer:
Windows 95/98/Me c:\windows\hosts
Windows NT/2000/XP Pro c:\winnt\system32\drivers\etc\hosts
Windows XP Home c:\windows\system32\drivers\etc\hosts
Benefits of the Hosts File:
(1.) Uses less resources:
By using a function built into your computer, you will be able to block advertising sites (or any other site you wish) without the need for any extra programs. This will cut down on memory and processor usage, which will free up your resources for other tasks.
(2.) Works on connections other than HTTP:
Most ad-blocking programs will only intercept IP calls going to the HTTP (or web) port on your computer. Other transfers can still get through. The Hosts file, however, will block IP calls on any port, whether it is HTTP, FTP, or whatever else you happen to be doing.
(3.) Eliminate many tracking and privacy concerns:
By intercepting the IP calls before they ever leave your computer, the Hosts file can prevent advertising and tracking companies from ever even knowing you are viewing a web page. This will keep them from profiling you and help you keep your privacy. All sites in the Hosts file entered with a 127.0.0.1 address will never be accessed. Sites that are not in the Hosts file may still track you and send you ads. See the notes section for more information.
To find out which advertisers may be tracking you, please visit this excellent web site.
(4.) The Hosts file is configurable:
Rather than relying on others to decide what sites to block for you, you may edit the Hosts file entirely on your own. This means you can put any site you wish into the Hosts file and that site will not be able to be accessed. You can use this to block advertisers, trackers, or sites you would not want your small children to see. You get to decide entirely what you wish to block, and you don't have to depend on someone else's judgement!
(5.) Increased browsing speed:
By placing sites into your Hosts file with their correct addresses, your computer does not need to ask another computer where to find a site. This can significantly speed up your surfing experience because your computer will go straight to that site instead of having to ask directions. Also, by keeping ads from being loaded using the blocking technique in the Hosts file, web pages will be viewable much more quickly since they won't have to load a lot of fancy graphics.
Some restrictions on the Hosts file:
(1.) It will not work with wildcards, such as *.whateveryouwantgoeshere.com.
(2.) It will not work with URL's that begin with IP numbers.
IP numbers are the numerical equivalent of the www.somesitenamehere.com address, and that is what your computer actually uses to find the web page. The names are there so that humans don't have to remember long strings of numbers. You would need to find the www.whatever.com address that the IP number represents, and then block that name instead of using the IP number. For example, Yahoo!'s address is www.yahoo.com, and its IP address is 204.71.200.67 We can block www.yahoo.com but not the IP address. The reason for this is that Hosts is used to determine IP addresses. If we already know the IP address, Hosts will not be consulted and so can not block the site. I do not recommend actually blocking Yahoo! though, as it is a great search engine!
(3.) It will not work with ads that are served from the same site you are viewing.
The reason for this is that the Hosts file must block an entire site, and can not block subdirectories or pathnames on a site. For example, you could not block www.netscape.com/ads/ because you can't block subdirectories. You would need to block the entire www.netscape.com server, and that would leave you without access to Netscape's site. So you will have to use a different method to eliminate ads that come from the site you are viewing, such as an ad-blocking program.
(4.) It may cause some sites to quit working properly.
If you put the wrong server into your hosts file, it may mean that certain websites will no longer be viewable as they normally would be. To remedy this, remove the entry of the site you wish to unblock from your hosts file. Please see the FAQ section for more on this. In particular, you may notice sites that rely on Akamai's servers will not function properly if Akamai is in your Hosts file.
The LMHOSTS File
The LMHOSTS file is a static ASCII file used to resolve NetBIOS names to IP addresses of remote computers running Windows NT and other NetBIOS-based hosts. This method is oldest method of resolving computer name to IP address. Every client must have this file in order to resolve NetBIOS names. It is located in winnt\system32\drivers\etc directory.
Contents of LMHOST File
#PRE : Defines which entries should be initially preloaded as permanent entries in the name cache. Preloaded entries reduce network broadcasts, because names are resolved from cache rather than from broadcast or by parsing the LMHOSTS file. Entries with a #PRE tag are loaded automatically at initialization or manually by typing nbtstat -R at a command prompt.
#DOM:[domain_name] : Facilitates domain activity, such as logon validation over a router, account synchronization, and browsing.
#NOFNR : Avoids using NetBIOS-directed name queries for older LAN Manager UNIX systems.
#BEGIN_ALTERNATE & #END_ALTERNATE : Defines a redundant list of alternate locations for LMHOSTS files. The recommended way to #INCLUDE remote files is using a Universal Naming Convention (UNC) path, to ensure access to the file. Of course, the UNC names must exist in the LMHOSTS file with a proper IP address to NetBIOS name translation.
#INCLUDE : Loads and searches NetBIOS entries in a separate file from the default LMHOSTS file. Typically, an #INCLUDE file is a centrally located shared LMHOST file.
#MH : Adds multiple entries for a multihomed computer.
<>14.what are the benefits of file and print server
print server
The benefit of having a print server is you can have many Macintoshes print to one LaserWriter. By using the direct method, you get into a waiting game. The first one who looks for it when it is idle gets it. The Print Server queues up all printing requests and makes sure the printer has no idle time as long as a print job is ready. The Queue above shows there is one print job printing and the server is waiting for another print job. The Log above shows you any messages which came from the Printer
<>15.What is ISDN / Lease line
ISDN
(Integrated Services Digital Network) - Digital telephony scheme that allows a user to connect to the Internet over standard phone lines at speeds higher than a 56K modem allows.
Abbreviation of integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second).
There are two types of ISDN:
- Basic Rate Interface (BRI) -- consists of two 64-Kbps B-channels and one D-channel for transmitting control information.
- Primary Rate Interface (PRI) -- consists of 23 B-channels and one D-channel (
The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fiber optic cables and is not widely available.
Lease line
A dedicated Common carrier circuit providing point-to-point or multipoint network connection, reserved for the permanent and private use of a customer . Also called a Private Line. A dedicated Common carrier circuit providing point-to-point or multipoint network connection, reserved for the permanent and private use of a customer . Also called a Private Line.
A Leased Line, also known as a ‘private circuit’ or ‘T1 leased line’, is a permanent dedicated communication link between two points. The link is separate from the public telephone network and is reserved exclusively for the leased line purchaser. Where a company's Internet usage is intensive, a leased line provides a far more cost-effective connectivity solution than more traditional ones such as ISDN.
A leased line can be a twisted pair, coax or fibre optic cable and may involve all sorts of other hardware such as coils, transformers, amplifiers and regenerators. Leased lines have varying data transfer rates the highest being a T1 line, which provides a maximum speed of 1.544Mbps. These transfer rates can be divided between voice and data signals using multiplexing techniques. If the leased line is being used to carry voice data then the line can also be connected to a phone system.
Large companies generally use leased lines to connect several geographically different networks within their organisation. The lease line is also widely used to connect offices to the web via a point of presence (POP), which is a fast connection directly to the Internet. A T1 leased line can connect over hundreds of users to the Internet effortlessly as long they are just browsing, a problem would only occur if they were to all start downloading files like MP3s.
<>16.what is Clustering
Clustering is a nonlinear activity that generates ideas, images and feelings around a stimulus word. As students cluster, their thoughts tumble out, enlarging their word bank for writing and often enabling them to see patterns in their ideas. Clustering may be a class or an individual activity.
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Clustering is the use of multiple computers and storage devices to create what seems to be a single system. Clustering is often used to increase a system's availability and for load balancing on highly-trafficked Web sites.
A server architecture that emulates multiprocessing by interconnecting two or more individual computers in order to share the application processing load. Microsoft's future clustering technology for Windows NT now carries the code name Wolfpack. A number of third parties offer proprietary clustering hardware and software for Windows NT Server 4.0.
A technique in which two or more servers are interconnected and can access a common storage pool. Clustering prevents the failure of a single file server from denying access to data and adds computing power to the network for large numbers of users.
<>17.What is
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<>18.what is POP3 and IMAP
POP3
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POP3 (Post Office Protocol 3) is the most recent version of a standard protocol for receiving e-mail. POP3 is a client/server protocol in which e-mail is received and held for you by your Internet server. Periodically, you (or your client e-mail receiver) check your mail-box on the server and download any mail, probably using POP3. This standard protocol is built into most popular e-mail products, such as Eudora and Outlook Express. It's also built into the Netscape and Microsoft Internet Explorer browsers.
POP3 is designed to delete mail on the server as soon as the user has downloaded it. However, some implementations allow users or an administrator to specify that mail be saved for some period of time. POP can be thought of as a "store-and-forward" service.
An alternative protocol is Internet Message Access Protocol (IMAP). IMAP provides the user more capabilities for retaining e-mail on the server and for organizing it in folders on the server. IMAP can be thought of as a remote file server.
POP and IMAP deal with the receiving of e-mail and are not to be confused with the Simple Mail Transfer Protocol (SMTP), a protocol for transferring e-mail across the Internet. You send e-mail with SMTP and a mail handler receives it on your recipient's behalf. Then the mail is read using POP or IMAP.
The conventional port number for POP3 is 110.
A port number is a way to identify a specific process to which an Internet or other network message is to be forwarded when it arrives at a server. For the Transmission Control Protocol and the User Datagram Protocol, a port number is a 16-bit integer that is put in the header appended to a message unit. This port number is passed logically between client and server transport layers and physically between the transport layer and the Internet Protocol layer and forwarded on.
For example, a request from a client (perhaps on behalf of you at your PC) to a server on the Internet may request a file be served from that host's File Transfer Protocol (FTP) server or process. In order to pass your request to the FTP process in the remote server, the Transmission Control Protocol (TCP) software layer in your computer identifies the port number of 21 (which by convention is associated with an FTP request) in the 16-bit port number integer that is appended to your request. At the server, the TCP layer will read the port number of 21 and forward your request to the FTP program at the server.
Some services or processes have conventionally assigned permanent port numbers. These are known as well-known port numbers. In other cases, a port number is assigned temporarily (for the duration of the request and its completion) from a range of assigned port numbers. This is called an ephemeral port number.
IMAP
IMAP (Internet Message Access Protocol) is a standard protocol for accessing e-mail from your local server. IMAP (the latest version is IMAP Version 4) is a client/server protocol in which e-mail is received and held for you by your Internet server. You (or your e-mail client) can view just the heading and the sender of the letter and then decide whether to download the mail. You can also create and manipulate multiple folders or mailboxes on the server, delete messages, or search for certain parts or an entire note. IMAP requires continual access to the server during the time that you are working with your mail.
A less sophisticated protocol is Post Office Protocol 3 (POP3). With POP3, your mail is saved for you in a single mailbox on the server. When you read your mail, all of it is immediately downloaded to your computer and, except when previously arranged, no longer maintained on the server.
IMAP can be thought of as a remote file server. POP3 can be thought of as a "store-and-forward" service.
POP3 and IMAP deal with the receiving of e-mail from your local server and are not to be confused with Simple Mail Transfer Protocol (SMTP), a protocol used for exchanging e-mail between points on the Internet. Typically, SMTP is used for sending only and POP3 or IMAP are used to read e-mail.
<>19.How will you move mailbox from one site to other
The Users have outlook 2000 point to the DomainA.COM Mailbox. Exchange is set to forward and not leave a copy any messages sent to the DomianB.Net mailbox to the DomainA.COM Mailbox.
It is done this way due to our Corporate Structure.
DomainA is the Corporate Entity, and Domain B is our Division.
We Primarily Communicate as DomainA, but occasionally we need to send messages out as Domain B. THe users know to enter their Domain B account in Sent From so it goes out correctly.
This Method works great except for one thing.
We have GFI Main Essentials as our SPAM filter.
It is automatically set up to put any SPAM messages in a SPAM folder in the Mailbox it was sent to. The SPAM messages for the Domain B mailbox are not being forwarded to the Domain A mailbox.
My only solution so far (THAT MAY WORK) is to set thier Outlook to also open mailbox B, and put the SPAM folder in the Outlook Bar. However not all users use the Outlook Bar and I do not want them having to look at multiple folders for SPAM
I tried to put a Rule in the SPAM folder to move it, but Rules only applied to the Inbox. I also tried on the Exchage server to go to the M Drive, Navigated to the SPAM folder and move the messages to the Correct SPAM folder. I get an error that the messages already exhists when I do that. If I Copy, than Delete I can move them in the M Drive, but when checking Outlook they are still in the Origianal SPAM foler..
<>20.How will you restore the backup in exchange (offline / Online )
Email systems depend on many hardware and software components. If any element fails to operate in the required manner, if the hardware suffers a catastrophic failure, or if a physical disaster such as an electricity outage afflicts the hardware, you must have good system backups to get users back online as quickly as possible.
The Exchange 2000 Server installation procedure enhances the standard Windows 2000 Server Backup utility (ntbackup.exe) to support the Exchange Store's transactional nature. These enhancements add support for Exchange 2000's .edb and .stm file formats, let backup agents (i.e., ntbackup.exe or third-party products) copy databases to tape without shutting down Exchange services, and let you select which servers and databases to back up or restore. Understanding the basics of the most important and useful disaster-recovery processes—including full backups, snapshot and clone backups, and the general recovery procedure—can help you prepare for disasters and recover from them quickly.
<>21.What is VPN
pronounced as separate letters) Short for virtual private network, a network that is constructed by using public wires to connect nodes. For example, there are a number of systems that enable you to create networks using the Internet as the medium for transporting data. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted.
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<>A virtual private network (VPN) is a way to use a public telecommunication infrastructure, such as the Internet, to provide remote offices or individual users with secure access to their organization's network. A virtual private network can be contrasted with an expensive system of owned or leased lines that can only be used by one organization. The goal of a VPN is to provide the organization with the same capabilities, but at a much lower cost.
A VPN works by using the shared public infrastructure while maintaining privacy through security procedures and tunneling protocol s such as the Layer Two Tunneling Protocol ( L2TP ). In effect, the protocols, by encrypting data at the sending end and decrypting it at the receiving end, send the data through a "tunnel" that cannot be "entered" by data that is not properly encrypted. An additional level of security involves encrypting not only the data, but also the originating and receiving network addresses.
<>22.Difference P2, P3, P4, Celeron
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<><>23.What is Ldap.
. LDAP (Lightwight Directory Acess Protocol)
LDAP is protocol that define how AD service is designed and how objects are managed in ADs. It defines the schema of AD. It defines how objects are organized in AD. It also defines how objects or resources can be access from AD. All objects naming in AD is based on LDAP protocol.
LDAP Namaing of objects
CN=Schema,CN=Configuration,DC=forest name,DC=forest root
eg : CN=Ajay Raul, CN=Users, DN=Vision, DC=com
In the above example Ajay Raul is username Full name and Vision.com is domain name
LDAP Ports
The connections via the LDAP protocol between a client and DSA use either a Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). The table below lists the protocol sockets used in different access modes:
Function Port
LDAP 389
LDAP Secure Sockets Layer (SSL) 636
Global Catalog (GC) 3268
Global Catalog Secure Sockets Layer 3269
24) What is ADS.
Active Directory Support Files
The engine used by Active Directory is based on Microsoft's Jet database technology. Jet uses a b-tree file structure with transaction logs to ensure recoverability in the event of a system or drive failure.
When you promote a server to a domain controller, you select where to put the Active Directory files. The default path is in the boot partition under \Windows\NTDS. Generally, it is a good idea to put them on a separate volume from the operating system files to improve performance.
25)What is directory service ? and what is active directory service ?
In simple a directory service can be define as "The friendly telephone operator who guides or looks up people's phone numbers for your assistance.". If the directory is the actual data—the list of people and telephone numbers—the operators and the method for calling them is the directory service. In windows 2000 Active Directory is a database while the computers which maintains this database are called as Domain Controllers.
In the field of computing there are various types of directory developed the development of networking begins, like
Microsoft - Active Directory Service
Xerox - Grapevine
ITU - X.500
IEEE - DNS (Domain Naming Service)
Netware - NDS (Novell Directory Service)
RFC - LDAP (Light Weight Directory Access Protocol)
Active Directory Service
ADS is a truly network directory that includes all the features and benefits of traditional directory service. In November 1996, Microsoft delivered the first preview of Active Directory for developers at the Professional Developers Conference held in
26)How big is active directory service ?
Active Directory : 100,000 users, 100,000 computers, 10,000 groups, 10,000 printers, and 10,000 volumes. The size of the resulting Ntds.dit is about 1,400 MB, or 1.4 gigabytes! This is with minimal attributes set on the objects. If all the attributes are set and new schema is update then the size can grow too long.
27) What is Schema ?
Schema in nothing but a structure which define what objects and their attributes can be stored in ADS. When a domain is setup it contains a default schema know as DIT (Directory Information Tree). There are over 140 predefines classes and over 840 attributes stored in DIT. SCHMMGMT.MSC is used to view the schema of ADS
28) What is encryption? And how encryption works ?
Encryption :
Encryption is a process of disguising a message or data in such a way as to hide its substance. Encryption is the process of converting data into a format that cannot be read by another user. Once a user has encrypted a file, the file automatically remains encrypted whenever the file is stored on disk and no other user can decrypt it.
Decryption is the process of converting data from encrypted format back to its original format. Once a user has decrypted a file, the file remains decrypted whenever the file is stored on disk.
Windows 2000 includes Encrypting File System (EFS) allows users to store their on-disk data in encrypted format. Encryption facility is available on for NTFS partition only.
EFS provides the following features:
<>· <>Users can encrypt their files when storing them on disk. Encryption is as easy as selecting a check box in the file's Properties dialog box.
<>· <>Accessing encrypted files is fast and easy. Users see their data in plain text when accessing the data from disk.
<>· <>Encryption of data is accomplished automatically, and is completely transparent to the user.
<>· <>Users can actively decrypt a file by clearing the Encryption check box on the file's Properties dialog box.
<>· <>Administrators can recover data that was encrypted by another user. This ensures that data is accessible if the user that encrypted the data is no longer available or has lost their private key.
EFS only encrypts data when it is stored on disk. To encrypt data as it is transported over a TCP/IP network, two optional features are available--Internet Protocol security (IPSec) and PPTP encryption
How Encryption works
Encryption of files works as follows:
<>· <>Each file has a unique file encryption key, which is later used to decrypt the file's data.
<>· <>The file encryption key is in itself encrypted--it is protected by the user's public key corresponding to the user's EFS certificate.
<>· <>The file encryption key is also protected by the public key of an authorized recovery agent.
Decryption of files works as follows:
<>· <>To decrypt a file, the file encryption key must first be decrypted. The file encryption key is decrypted when the user has a private key that matches the public key.
<>· <>The user is not the only person that can decrypt the file encryption key. A recovery agent can also decrypt the file encryption key, by using the recovery agent's private key.
<>· <>Once the file encryption key is decrypted, it can be used by either the user or the recovery agent to decrypt the data in the file.
NOTE : Encrypted data is not encrypted when in transit over the network, but only when stored on disk. The exception to this is when your system includes Internet Protocol security (IPSec). IPSec encrypts data while it is transported over a TCP/IP network. Encrypted files are not accessible from Macintosh clients. You cannot encrypt a compress file.
29) what is DFS and reasons for using dfs? (distributed file system )
Distributed file system overview
The Distributed file system (Dfs) allows system administrators to make it easier for users to access and manage files that are physically distributed across a network. With Dfs, you can make files distributed across multiple servers appear to users as if they reside in one place on the network. Users no longer need to know and specify the actual physical location of files in order to access them.
For example, if you have marketing material scattered across multiple servers in a domain, you can use Dfs to make it appear as though all of the material resides on a single server. This eliminates the need for users to go to multiple locations on the network to find the information they need.
Reasons for using Dfs
You should consider implementing Dfs if:
<>· <>Users who access shared folders are distributed across a site or sites.
<>· <>Most users require access to multiple shared folders.
<>· <>Server load balancing could be improved by redistributing shared folders.
<>· <>Users require uninterrupted access to shared folders.
<>· <>Your organization has Web sites for either internal or external use.
Types of DFs
Using the Dfs console, you can implement a distributed file system in either of two ways--either as a stand-alone distributed file system, or as a domain-based distributed file system.
A stand-alone Dfs root:
<>· <>Does not use Active Directory.
<>· <>Cannot have root-level Dfs shared folders.
<>· <>Has a limited hierarchy. A standard Dfs root can have only a single level of Dfs links.
<>· <>Replication facility is not available.
A domain-based Dfs root:
<>· <>Must be hosted on a domain member server.
<>· <>Has its Dfs topology automatically published to Active Directory.
<>· <>Can have root-level Dfs shared folders.
<>· <>Does not have a limited hierarchy. A domain-based Dfs root can have multiple levels of Dfs links.
<>· <>Replication facility is available.
30)How DHCP works? And what is DHCP relay agent?
DHCP stands for "Dynamic Host Configuration Protocol".
DHCP automatically assigns IP addresses to computers. DHCP overcomes the limitations of configuring TCP/IP manually. DHCP is an extension of the Boot Protocol (BOOTP). BOOTP enables diskless clients to start up and automatically configure TCP/IP. DHCP centralizes and manages the allocation of TCP/IP configuration information by automatically assigning IP addresses to computers configured to use DHCP. Implementing DHCP eliminates some of the configuration problems associated with manually configuring TCP/IP.
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Each time a DHCP client starts, it requests IP addressing information from a DHCP server, including the IP address, the subnet mask, and optional values. The optional values may include a default gateway address, Domain Name System (DNS) address, and Windows Internet Name Service (WINS) server address. When a DHCP server receives a request, it selects IP addressing information from a pool of addresses defined in its database and offers it to the DHCP client. If the client accepts the offer, the IP addressing information is leased to the client for a specified period of time. If there is no available IP addressing information in the pool to lease to a client, the client cannot initialize TCP/IP.
How DHCP Works
DHCP uses a four-phase process to configure a DHCP client as given below
1) IP lease discover : The client initializes a limited version of TCP/IP and broadcasts a request for the location of a DHCP server and IP addressing information.
2) IP lease offer : All DHCP servers that have valid IP addressing information available send an offer to the client.
3) IP lease request : The client selects the IP addressing information from the first offer it receives and broadcasts a message requesting to lease the IP addressing information in the offer.
4) IP lease acknowledgment : The DHCP server that made the offer responds to the message, and all other DHCP servers withdraw their offers. The IP addressing information is assigned to the client and an acknowledgment is sent. The client finishes initializing and binding the TCP/IP protocol. Once the automatic configuration process is complete, the client can use all TCP/IP services and utilities for normal network communications and connectivity to other IP hosts.
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DHCP Relay Agent
A relay agent is a small program that relays DHCP/BOOTP messages between clients and servers on different subnets. The DHCP Relay Agent component provided with the Windows 2000 router is a BOOTP relay agent that relays DHCP messages between DHCP clients and DHCP servers on different IP networks. For each IP network segment that contains DHCP clients, either a DHCP server or a computer acting as a DHCP relay agent is required.
To add the DHCP Relay Agent
<>· <>Click Start, point to Programs, point to Administrative Tools, then click Routing And Remote Access.
<>· <>In the console tree, click Server name\IP Routing\General.
<>· <>Right-click General, then click New Routing Protocol.
<>· <>In the Select Routing Protocol dialog box, click DHCP Relay Agent, then click OK.
31) On disk management explain basic disk vs Dynamin disk?
Basic disks are the logical disk structure that use the same disk structure used in Windows NT 4.0 and previous operating systems all the way back to MS-DOS. That is, they are divided into primary and extended partitions, and logical drives can be created within extended partitions.
Dynamic disks use a new disk structure that was introduced in Windows 2000 and now in windows 2003 .In dynamic disk partitions are called as Volumes. With dynamic disks, you can extend simple volumes (make them bigger without reformatting and losing data) to any empty space on any dynamic disk, create spanned volumes across multiple physical disks and create fault tolerant (RAID 1 and 5) volumes.
Unlike basic disk, dynamic disk does not use MBR to store partition table. Instead they use a private database at the end of the disk called as LVM (Logical Volume Manager). This database is of 1MB and replicated to all dynamic in a machine. Windows 2003 does not support Windows NT partition that uses RAID level when you upgrade from NT to 2003.
The following are some limitations of using dynamic disks:
<>· <>Dynamic disks are currently not supported on laptop computers.
<>· <>Removable media and disks attached via FireWire (IEEE 1394), Universal Serial Bus (USB), or shared SCSI buses cannot be converted to dynamic.
<>· <>You can install Windows Server 2003 only onto a dynamic volume that was converted from a basic boot or system partition.You cannot install onto a dynamic volume that was created from free space.This is because there must be an entry in the partition table for the setup program to recognize the volume, and such an entry does not exist on a newly created dynamic volume.
<>· <>Even though Windows 2000, XP Professional, and Server 2003 all use dynamic disks, you cannot convert a basic disk that holds multiple instances of these operating systems to dynamic.The operating systems installed on the disk will not start if you do this.
<>· <>Dynamic disks are not supported by Windows Cluster Service. If you need the features of dynamic disks on a clustered shared disk, you can use a third-party program called Veritas Volume Manager 4.0 to accomplish this.
31) What is ICS ( intrnet connection sharing.)
Internet connection sharing
With the Internet connection sharing feature of Network and Dial-up Connections, you can use Windows 2000 to connect your home network or small office network to the Internet. For example, you might have a home network that connects to the Internet by using a dial-up connection. By enabling Internet connection sharing on the computer that uses the dial-up connection, you are providing network address translation, addressing, and name resolution services for all computers on your home network.
After Internet connection sharing is enabled, and users verify their networking and Internet options, home network or small office network users can use applications such as Internet Explorer and Outlook Express as if they were already connected to the Internet Service Provider (ISP). The Internet connection sharing computer then dials the ISP and creates the connection so that the user can reach the specified Web address or resource. To use the Internet connection sharing feature, users on your home office or small office network must configure TCP/IP on their local area connection to obtain an IP address automatically. Also, home office or small office network users must configure Internet options for Internet connection sharing.
The Internet connection sharing feature is intended for use in a small office or home office where network configuration and the Internet connection are managed by the computer running Windows 2000 where the shared connection resides. It is assumed that on its network, this computer is the only Internet connection, the only gateway to the Internet, and that it sets up all internal network addresses.
You might need to configure applications and services on the Internet connection sharing computer to work properly across the Internet. For example, if users on your home network want to play the Diablo game with other users on the Internet, you must configure the Diablo application on the connection where Internet connection sharing is enabled. Conversely, services that you provide must be configured so that Internet users can access them. For example, if you are hosting a Web server on your home network and want Internet users to be able to connect to it, you must configure the Web server service on the Internet connection sharing computer.
Important Points
<>· <>To configure Internet connection sharing, you must be a member of the Administrators group.
<>· <>You should not use this feature in an existing network with other Windows 2000 Server domain controllers, DNS servers, gateways, DHCP servers, or systems configured for static IPaddresses. If you are running Windows 2000 Server, and one or more of these components exist, you must use network address translation to achieve the same result.
<>· <>A computer with Internet connection sharing needs two connections. One connection, typically a LAN adapter, connects to the computers on the home network. The other connection connects the home network to the Internet. You need to ensure that Internet connection sharing is enabled on the connection that connects your home network to the Internet. By doing this, the home network connection appropriately allocates TCP/IP addresses to its own users, the shared connection can connect your home network to the Internet, and users outside your home network are not at risk of receiving inappropriate addresses from your home network. By enabling Internet connection sharing on a connection, the Internet connection sharing computer becomes a Dynamic Host Configuration Protocol (DHCP) allocator for the home network. DHCP distributes TCP/IP addresses to users as they start up. If Internet connection sharing is enabled on the wrong network adapter, users outside your home network might be granted TCP/IP addresses by the home network DHCP allocator, causing problems on their own networks.
When you enable Internet connection sharing, the adapter connected to the home or small office network is given a new static IP address configuration. Consequently, TCP/IP connections established between any small office or home office computer and the Internet connection sharing computer at the time of enabling Internet connection sharing are lost and need to be reestablished.
Notes
<>· <>You cannot modify the default configuration of Internet connection sharing. This includes items such as disabling the DHCP allocator or modifying the range of private IP addresses that are distributed, disabling the DNS proxy, configuring a range of public IP addresses, or configuring inbound mappings. If you want to modify any of these items, you must use network address translation.
<>· <>If your home office users need to access a corporate network that is connected to the Internet by a tunnel server from an Internet connection sharing network, they need to create a virtual private network connection to tunnel from the computer on the Internet connection sharing network to the corporate tunnel server on the Internet. The VPN connection is authenticated and secure and creating the tunneled connection allocates proper IP addresses, DNS server addresses, and WINS server addresses for the corporate network. For more information about creating a virtual private network (VPN) connection.
32) What is RAS(remot access service).
Remote Access Service (RAS)
Windows 2000 Server remote access server(RAS), part of the integrated Routing and Remote Access service, connects remote or mobile workers to organization networks. Remote users can work as if their computers are physically connected to the network. Remote access is nothing but provide remote users to dial-in in our RAS server i.e. it allows inbound connection to RAS server using dial-up connection and various auth. protocol like PAP, MS-CHAP, SPAP, etc.
Users run remote access software (Dail-up connection) and initiate a connection to the remote access server(RAS Server). The remote access server, which is a computer running Windows 2000 Server and the Routing and Remote Access service, authenticates users and services sessions until terminated by the user or network administrator. All services typically available to a LAN-connected user (including file and print sharing, Web server access, and messaging) are enabled by means of the remote access connection.
A remote access server running Windows 2000 provides two different types of remote access connectivity:
1) Dial-up networking
Dial-up networking is when a remote access client makes a non-permanent, dial-up connection to a physical port on a remote access server by using the service of a telecommunications provider such as analog phone (PSTN), ISDN, or X.25. The best example of dial-up networking is that of a dial-up networking client who dials the phone number of one of the ports of a remote access server.
Dial-up networking over an analog phone or ISDN is a direct physical connection between the dial-up networking client and the dial-up networking server. You can encrypt data sent over the connection, but it is not required.
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2) Virtual private networking (VPN)
Virtual private networking is the creation of secured, point-to-point connections across a private network or a public network such as the Internet. A virtual private networking client uses special TCP/IP-based protocols called tunneling protocols to make a virtual call to a virtual port on a virtual private networking server. The various tunnelling protcol used for VPN are PPTP(Point to point tunneling protocol), L2TP (Layer-2 tunneling protocol). The best example of virtual private networking is that of a virtual private networking client who makes a virtual private network connection to a remote access server that is connected to the Internet. The remote access server answers the virtual call, authenticates the caller, and transfers data between the virtual private networking client and the corporate network.
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33) What is NOS(network operating system) ?
Network Operating System (NOS)
Network Operating Systems are availble to support a PC server based network.
All Microsoft Windows based operating systems support peer-to-peer networking. Specialized network operating system (NOS) software is required for a server-based network.
Example
Unix :- A popular, robust operating system that comes in several forms from different vendors.
Microsoft - Win NT-Server, Windows 2K Server
Apple Talk : - Mac OS
Lan Manager & Lan Server :- Developed by Microsoft and IBM that no longer very common.
34) What is topology?
Network Topologies
What is Topology?
It is physical way of communication, the configurations formed by the connections between devices on a Local Area Network (LAN) or between two or more LAN's.
It is important to make a distinction between a topology and an architecture. A topology is concerned with the physical arrangement of the network components.
There are three basic Network Topologies
<>· <>The Bus
<>· <>The Star
<>· <>The Ring
35) What is difference between SD-RAM AND DD-RAM .
<>· <>SD Ram is actually SDR SDRAM, and DD Ram is actually DDR SDRAM, though the former does not usually have the SDR in front of it. The letters SDR and DDR stand for Single Data Rate and Double Data Rate, and the letters SDRAM stand for Synchronous Dynamic Random Access Memory.
The main difference between SDR and DDR memory is speed. There are a lot of little differences, but the main one (IMHO) that affects the user is speed: DDR can transfer data at roughly twice the speed of SDR. More speedy data rates = better performance.
Just remember, the motherboard you are using must include the appropriate chipset to support the different RAM types. They are not interchangeable.
SDR SDRAM comes in three main flavors: PC66, PC100 and PC133. Each successive number refers to the bus speed of the RAM in MHz, thus PC66 runs at 66 MHz, PC100 runs at 100 MHz, etc. SDR SDRAM has 168 pins at the connector.
DDR SDRAM has 184 pins at the connector, which is one reason you can't just use DDR instead of SDR, and comes in many different flavors; PC2100 which runs at 266 MHz, PC2700 which runs at 333 MHz, PC3200 which runs at 400 MHz, etc. In order to know which type of RAM you need, you must know what your motherboard supports
36) What is difference between DD-RAM AND RD-RAM.
Short for Rambus DRAM, a type of memory (DRAM) developed by Rambus, Inc. Whereas the fastest current memory technologies used by PCs (SDRAM) can deliver data at a maximum speed of about 100 MHz, RDRAM transfers data at up to 800 MHz.
In 1997, Intel announced that it would license the Rambus technology for use on its future motherboards, thus making it the likely de facto standard for memory architectures. However, a consortium of computer vendors is working on an alternative memory architecture called SyncLink DRAM (SLDRAM).
RDRAM is already being used in place of VRAM in some graphics accelerator boards. As of late 1999, Intel has been using RDRAM in its Pentium III Xeon processors and more recently in its Pentium 4 processors. Intel and Rambus are also working a new version of RDRAM, called nDRAM, that will support data transfer speeds at up to 1,600 MHz.
The Pentium 4 is known to crave memory bandwidth above and over everything else. The processor throws fits like a baby when there is not enough memory bandwidth, something which can often keep it from performing up to its potential. This was evident when Intel released their original i845 chipset which allowed a Pentium 4 to be run with conventional SDRAM (hint: avoid like the plague).
Often a P4 equipped with SDRAM, running at similar clock speeds could not beat a P3 at 1 GHz in terms of performance! DDR alleviated the memory bandwidth bottleneck somewhat with the i845D, delivering 2.1 GB/s worth of bandwidth as opposed to the 1.08 GB/s SDRAM offered. That is still a far cry from the 3.2 GB/s RDRAM can supply though, and today we're going to take a look at whether the i850 "RDRAM" chipset is that much faster then the i845D "DDR" chipset.
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Many times readers have been writing in to ask; "Is RDRAM really necessary for a Pentium 4?" or maybe "I can't afford RDRAM, can I get by on DDR?" My personal favorite is; "I'm a speed freak on a budget, but can I get good performance with a P4/DDR combo? ".
Well today I hope we set these questions to rest and answer what has been on the minds of many; if Spiderman and Superman were in a battle who would win? We also plan on pitting RDRAM vs. DDR RAM and seeing which memory will be victorious - it is a battle royal that even the great Spidy can 'sense'.
There are a whole bunch of DDR chipsets now for the Pentium 4, but we're going to be focusing on Intel's own i845D. Why you ask? Intel has always produced fast and very stable chipsets (other then the i820) and the i845D is no exception. Based on the earlier i845 which was a very stable chipset in it's own, the i845D only brings DDR capability to the table and nothing else. Actually there are no real differences between the i845 or i845D. Sure there's an official revision difference, but basically the i845D is the i845 with DDR enabled.
The i850 board we are testing with is the nice red MSI 850 Pro5 which has official support for 400 MHz based Pentium 4's using the Socket 478 format. We had a few i845D based motherboards to choose from and eventually decided to keep it in the family and test on the MSI 845 Ultra. Our testing processor is a Pentium 4 2.0 GHz Williamette with 256KB L2 cache.
Question: I just bought a computer that has SDRAM and now I'm hearing that DDR and Rambus memory are better. What are these new types of memory and how do they work? Did I buy the wrong thing? Help!
Answer: You heard right, DDR and Rambus DRAM are two new types of memory promising to make computers run faster. But before we discuss them, relax! They will NOT make SDRAM obsolete in the near future.
First, let's start with a quick review. In the last few years, SDRAM
(synchronous DRAM) has become the standard type of memory for PCs. The main reason for this is that SDRAM is tied to the front-side bus clock in your system. SDRAM and the bus execute instructions at the same time rather than one of them having to wait for the other. As bus speeds have increased beyond 100MHz, this has improved system performance.
DDR SDRAM
DDR (double data rate) memory is the next generation SDRAM. Like
SDRAM, DDR is synchronous with the system clock. The big difference between DDR and SDRAM memory is that DDR reads data on both the rising and falling edges of the clock signal. SDRAM only carries information on the rising edge of a signal. Basically this allows the DDR module to transfer data twice as fast as SDRAM. For example, instead of a data rate of 133MHz, DDR memory transfers data at 266MHz.
DDR modules, like their SDRAM predecessors, are called DIMMs. They use motherboard system designs similar to those used by SDRAM; however, DDR is not backward compatible with SDRAM-designed motherboards. DDR memory supports both ECC (error correction code, typically used in servers) and non-parity (used on desktops/laptops.)
If your system or motherboard requires DDR, you can purchase the upgrades you need through Crucial's Memory Selector™.
Rambus DRAM
Rambus memory (RDRAM®) is a revolutionary step from SDRAM. It's a new memory design with changes to the bus structure and how signals are carried. Rambus memory sends less information on the data bus (which is 18 bits wide as opposed to the standard 32 or 64 bits) but it sends data more frequently. It also reads data on both the rising and falling edges of the clock signal, as DDR does. As a result, Rambus memory is able to achieve effective data transfer speeds of 800MHz and higher.
Another difference with Rambus memory is that all memory slots in the motherboard must be populated. Even if all the memory is contained in a single module, the "unused" sockets must be populated with a PCB, known as a continuity module, to complete the circuit.
Rambus DRAM modules are known as RIMM™ modules (Rambus inline memory modules). Rambus memory supports both ECC and non-ECC applications.
Production Challenges
One of the challenges Rambus memory currently faces is that it is expensive to produce compared to SDRAM and DDR. Rambus memory is proprietary technology of Rambus Inc. Manufacturers that want to produce it are required to pay a royalty to Rambus Inc., whereas DDR designs are open architecture. Other cost factors for Rambus memory include additional module manufacturing and testing processes and a larger die size. Rambus die (chips) are much larger than SDRAM or DDR die. That means fewer parts can be produced on a wafer.
Performance
Now for the million-dollar question: How do DDR and Rambus memory compare performance wise? Sorry, I know you don't want to hear this — that depends. Both technologies have their own ardent supporters and we have seen several different benchmarks to date that provide conflicting results.
On the surface, it seems simple: Data flow at 800MHz is faster than data flow at 266MHz, right? Unfortunately, it isn't that simple. While Rambus modules may have the ability to transfer data faster, it appears to have higher latency (the amount of time you have to wait until data flows) than that of a DDR system. In other words, the first data item transferred in a Rambus transaction takes longer to initiate than the first data item moved in a DDR system. This is due in part to how the systems are constructed.
In a DDR or SDRAM system, each DIMM is connected, individually and in parallel, to the data bus. So whether you have a single DIMM or multiple DIMMs, the amount of time it takes to initiate a data transfer is effectively unchanged.
In a Rambus system, RIMM modules are connected to the bus in a series. The first data item transferred must pass through each RIMM module before it reaches the bus. This makes for a much longer distance for the signal to travel. The result is higher latency. That's not necessarily a problem in an environment where data transactions involve lengthy streams of data, such as gaming. But it can become an issue in environments where many small transactions are initiated regularly, such as a server.
To further explain, here's an example that we can all relate to — driving your car to the store. You can take the roundabout freeway and drive 20 miles at 70 MPH. Or, you can take a more direct route and drive just 5 miles at 50 MPH. You might go faster on the freeway but you'll get to the store (Memory Controller) faster on the straight-line route.
Looking to the Future
So which technology will become the memory of choice for the computer industry? That probably won't be clear until sometime in the near future. However, it really doesn't matter to a certain extent.
Generally speaking, motherboards are built to support one type of memory. You cannot mix and match more than one type of SDRAM, DDR, or Rambus memory on the same motherboard in any system. They will not function and will not even fit in the same sockets. The right type of memory to use is the one that your motherboard takes! And no matter what type of memory you use, more is typically better. A memory upgrade is still one of the most cost-effective ways to improve system performance.
At this point in time, the market for DDR and Rambus memory is relatively small. However, it is growing. Crucial currently offers DDR and will offer other new technologies as the market dictates.
37) What is peer to peer network.
A network in which there are no dedicated servers among the computers. All computers share resources such as files and printers therefore acting as both client and server.
A communication network without a dedicated server. Each computer in the network can act as a client and a server. Any computer can access files on any other computer in the network.
Windows Peer-to-Peer Networking
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Windows Peer-to-Peer Networking is an operating system component that enables the creation of new peer-to-peer (P2P) applications for computers running Windows XP (Service Pack 1 and later). P2P applications can utilize the powerful personal computers that exist at the edge of the Internet to create exciting, distributed experiences. P2P networking can also allow existing applications to work together in new and useful ways.peer-to-peer architecture
Often referred to simply as peer-to-peer, or abbreviated P2P, a type of network in which each workstation has equivalent capabilities and responsibilities. This differs from client/server architectures, in which some computers are dedicated to serving the others. Peer-to-peer networks are generally simpler, but they usually do not offer the same performance under heavy loads.
38) What is CMOS ?
Short for complementary metal oxide semiconductor. Pronounced see-moss, CMOS is a widely used type of semiconductor. CMOS semiconductors use both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor. This makes them particularly attractive for use in battery-powered devices, such as portable computers. Personal computers also contain a small amount of battery-powered CMOS memory to hold the date, time, and system setup parameters.
The CMOS or Complementary Metal Oxide Semiconductor is an on-board semiconductor chip. Which requires very low power generated from various types of CMOS batteries which are shown below. This chip is used to store important system information and configuration settings while the computer is off and on.
Types of CMOS batteries - The following is a listing of the types of batteries found in computer to power the CMOS memory. The most common type of battery is the Coin cell battery (Lithium Battery) the coin cell battery is the size of a dime, as shown below.
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Life time of a CMOS battery - The standard life time of a CMOS battery is around 10 Years, however this amount of time can change depending on the use and environment that the computer resides.
In CMOS (Complementary Metal-Oxide Semiconductor) technology, both N-type and P-type transistors are used to realize logic functions. Today, CMOS technology is the dominant semiconductor technology for microprocessors, memories and application specific integrated circuits (ASICs). The main advantage of CMOS over NMOS and bipolar technology is the much smaller power dissipation. Unlike NMOS or bipolar circuits, a CMOS circuit has almost no static power dissipation. Power is only dissipated in case the circuit actually switches. This allows to integrate many more CMOS gates on an IC than in NMOS or bipolar technology, resulting in much better performance.
The following applets demonstrate the N-type and P-type transistors used in CMOS technology, the basic CMOS inverter, NAND and NOR gates, and an AOI32 complex gate.
Finally, it demonstrates the CMOS transmission-gate and a transmisson-gate D-latch.
The first applet illustrates the function of both N-type and P-type MOS transistors.
Click on the source and gate contacts of the transistors to toggle the corresponding voltage levels and watch the resulting output value on the drain contacts. The applet uses colors to display the different voltages.
- A logical '1' corresponding to electrical level VCC (typical values for current technolgies are +5V or +3.3V) is shown in red,
- a logical '0' (corresponding to 0V or GND) in blue.
- A floating wire (not connected to either VCC or GND) is shown in orange.
How BIOS Works
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<>One of the most common uses of Flash memory is for the basic input/output system of your computer, commonly known as the BIOS (pronounced "bye-ose"). On virtually every computer available, the BIOS makes sure all the other chips, hard drives, ports and CPU function together.
Every desktop and laptop computer in common use today contains a microprocessor as its central processing unit. The microprocessor is the hardware component. To get its work done, the microprocessor executes a set of instructions known as software (see How Microprocessors Work for details). You are probably very familiar with two different types of software:
- The operating system - The operating system provides a set of services for the applications running on your computer, and it also provides the fundamental user interface for your computer. Windows 98 and Linux are examples of operating systems. (See How Operating Systems Work for lots of details.)
- The applications - Applications are pieces of software that are programmed to perform specific tasks. On your computer right now you probably have a browser application, a word processing application, an e-mail application and so on. You can also buy new applications and install them.
It turns out that the BIOS is the third type of software your computer needs to operate successfully. In this article, you'll learn all about BIOS -- what it does, how to configure it and what to do if your BIOS needs updating.
Configuring BIOS
In the previous list, you saw that the BIOS checks the CMOS Setup for custom settings. Here's what you do to change those settings.
To enter the CMOS Setup, you must press a certain key or combination of keys during the initial startup sequence. Most systems use "Esc," "
Once you have entered setup, you will see a set of text screens with a number of options. Some of these are standard, while others vary according to the BIOS manufacturer. Common options include:
- System Time/Date - Set the system time and date
- Boot Sequence - The order that BIOS will try to load the operating system
- Plug and Play - A standard for auto-detecting connected devices; should be set to "Yes" if your computer and operating system both support it
- Mouse/Keyboard - "Enable Num Lock," "Enable the Keyboard," "Auto-Detect Mouse"...
- Drive Configuration - Configure hard drives, CD-ROM and floppy drives
- Memory - Direct the BIOS to shadow to a specific memory address
- Security - Set a password for accessing the computer
- Power Management - Select whether to use power management, as well as set the amount of time for standby and suspend
- Exit - Save your changes, discard your changes or restore default settings
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<>Be very careful when making changes to setup. Incorrect settings may keep your computer from booting. When you are finished with your changes, you should choose "Save Changes" and exit. The BIOS will then restart your computer so that the new settings take effect.
The BIOS uses CMOS technology to save any changes made to the computer's settings. With this technology, a small lithium or Ni-Cad battery can supply enough power to keep the data for years. In fact, some of the newer chips have a 10-year, tiny lithium battery built right into the CMOS chip!
Updating Your BIOS
Occasionally, a computer will need to have its BIOS updated. This is especially true of older machines. As new devices and standards arise, the BIOS needs to change in order to understand the new hardware. Since the BIOS is stored in some form of ROM, changing it is a bit harder than upgrading most other types of software.
To change the BIOS itself, you'll probably need a special program from the computer or BIOS manufacturer. Look at the BIOS revision and date information displayed on system startup or check with your computer manufacturer to find out what type of BIOS you have. Then go to the BIOS manufacturer's Web site to see if an upgrade is available. Download the upgrade and the utility program needed to install it. Sometimes the utility and update are combined in a single file to download. Copy the program, along with the BIOS update, onto a floppy disk. Restart your computer with the floppy disk in the drive, and the program erases the old BIOS and writes the new one. You can find a BIOS Wizard that will check your BIOS at BIOS Upgrades.
Major BIOS manufacturers include:
As with changes to the CMOS Setup, be careful when upgrading your BIOS. Make sure you are upgrading to a version that is compatible with your computer system. Otherwise, you could corrupt the BIOS, which means you won't be able to boot your computer. If in doubt, check with your computer manufacturer to be sure you need to upgrade.
Booting the Computer
Whenever you turn on your computer, the first thing you see is the BIOS software doing its thing. On many machines, the BIOS displays text describing things like the amount of memory installed in your computer, the type of hard disk and so on. It turns out that, during this boot sequence, the BIOS is doing a remarkable amount of work to get your computer ready to run. This section briefly describes some of those activities for a typical PC.
After checking the CMOS Setup and loading the interrupt handlers, the BIOS determines whether the video card is operational. Most video cards have a miniature BIOS of their own that initializes the memory and graphics processor on the card. If they do not, there is usually video driver information on another ROM on the motherboard that the BIOS can load.
Next, the BIOS checks to see if this is a cold boot or a reboot. It does this by checking the value at memory address 0000:0472. A value of 1234h indicates a reboot, and the BIOS skips the rest of POST. Anything else is considered a cold boot.
If it is a cold boot, the BIOS verifies RAM by performing a read/write test of each memory address. It checks the PS/2 ports or USB ports for a keyboard and a mouse. It looks for a peripheral component interconnect (PCI) bus and, if it finds one, checks all the PCI cards. If the BIOS finds any errors during the POST, it will notify you by a series of beeps or a text message displayed on the screen. An error at this point is almost always a hardware problem.
The BIOS then displays some details about your system. This typically includes information about:
- The processor
- The floppy drive and hard drive
- Memory
- BIOS revision and date
- Display
Any special drivers, such as the ones for small computer system interface (SCSI) adapters, are loaded from the adapter, and the BIOS displays the information. The BIOS then looks at the sequence of storage devices identified as boot devices in the CMOS Setup. "Boot" is short for "bootstrap," as in the old phrase, "Lift yourself up by your bootstraps." Boot refers to the process of launching the operating system. The BIOS will try to initiate the boot sequence from the first device. If the BIOS does not find a device, it will try the next device in the list. If it does not find the proper files on a device, the startup process will halt. If you have ever left a floppy disk in the drive when you restarted your computer, you have probably seen this message.
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<>The BIOS has tried to boot the computer off of the floppy disk left in the drive. Since it did not find the correct system files, it could not continue. Of course, this is an easy fix. Simply pop out the disk and press a key to continue.
39) What is the difference between a Pentium and a Celeron processor?
Here are the most important similarities and differences between the Pentium 4 and the Celeron chips coming out today:
- Core - The Celeron chip is based on a Pentium 4 core.
- Cache - Celeron chips have less cache memory than Pentium 4 chips do. A Celeron might have 128 kilobytes of L2 cache, while a Pentium 4 can have four times that. The amount of L2 cache memory can have a big effect on performance.
- Clock speed - Intel manufactures the Pentium 4 chips to run at a higher clock speed than Celeron chips. The fastest Pentium 4 might be 60 percent faster than the fastest Celeron.
- Bus speed - There are differences in the maximum bus speeds that the processors allow. Pentium 4s tend to be about 30 percent faster than Celerons.
When you sort all this out and compare the two chips side by side, it turns out that a Celeron and a Pentium 4 chip running at the same speed are different beasts. The smaller L2 cache size and slower bus speeds can mean serious performance differences depending on what you want to do with your computer. If all you do is check e-mail and browse the Web, the Celeron is fine, and the price difference can save you a lot of money. If you want the fastest machine you can buy, then you need to go with the Pentium 4 to get the highest clock speeds and the fastest system bus.
40) How Microprocessors Work ?
If you have been shopping for a computer, then you have heard the word "cache." Modern computers have both L1 and L2 caches. You may also have gotten advice on the topic from well-meaning friends, perhaps something like "Don't buy that Celeron chip, it doesn't have any cache in it!"
It turns out that caching is an important computer-science process that appears on every computer in a variety of forms. There are memory caches, hardware and software disk caches, page caches and more. Virtual memory is even a form of caching. In this article, we will explore caching so you can understand why it is so important.
RAM and ROM
The previous section talked about the address and data buses, as well as the RD and WR lines. These buses and lines connect either to RAM or ROM -- generally both. In our sample microprocessor, we have an address bus 8 bits wide and a data bus 8 bits wide. That means that the microprocessor can address (28) 256 bytes of memory, and it can read or write 8 bits of the memory at a time. Let's assume that this simple microprocessor has 128 bytes of ROM starting at address 0 and 128 bytes of RAM starting at address 128.
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<>ROM stands for read-only memory. A ROM chip is programmed with a permanent collection of pre-set bytes. The address bus tells the ROM chip which byte to get and place on the data bus. When the RD line changes state, the ROM chip presents the selected byte onto the data bus.
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<>RAM stands for random-access memory. RAM contains bytes of information, and the microprocessor can read or write to those bytes depending on whether the RD or WR line is signaled. One problem with today's RAM chips is that they forget everything once the power goes off. That is why the computer needs
By the way, nearly all computers contain some amount of ROM (it is possible to create a simple computer that contains no RAM -- many microcontrollers do this by placing a handful of RAM bytes on the processor chip itself -- but generally impossible to create one that contains no ROM). On a PC, the ROM is called the BIOS (Basic Input/Output System). When the microprocessor starts, it begins executing instructions it finds in the BIOS. The BIOS instructions do things like test the hardware in the machine, and then it goes to the hard disk to fetch the boot sector (see How Hard Disks Work for details). This boot sector is another small program, and the BIOS stores it in RAM after reading it off the disk. The microprocessor then begins executing the boot sector's instructions from RAM. The boot sector program will tell the microprocessor to fetch something else from the hard disk into RAM, which the microprocessor then executes, and so on. This is how the microprocessor loads and executes the entire operating system.
41) How Ethernet Works
In today's business world, reliable and efficient access to information has become an important asset in the quest to achieve a competitive advantage. File cabinets and mountains of papers have given way to computers that store and manage information electronically. Coworkers thousands of miles apart can share information instantaneously, just as hundreds of workers in a single location can simultaneously review research data maintained online.
Computer networking technologies are the glue that binds these elements together. The public Internet allows businesses around the world to share information with each other and their customers. The global computer network known as the World Wide Web provides services that let consumers buy books, clothes, and even cars online, or auction those same items off when no longer wanted.
In this article, we will take a very close look at networking, and in particular the Ethernet networking standard, so you can understand the actual mechanics of how all of these computers connect to one another.
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Why Network?
Networking allows one computer to send information to and receive information from another. We may not always be aware of the numerous times we access information on computer networks. Certainly the Internet is the most conspicuous example of computer networking, linking millions of computers around the world, but smaller networks play a role in information access on a daily basis. Many public libraries have replaced their card catalogs with computer terminals that allow patrons to search for books far more quickly and easily. Airports have numerous screens displaying information regarding arriving and departing flights. Many retail stores feature specialized computers that handle point-of-sale transactions. In each of these cases, networking allows many different devices in multiple locations to access a shared repository of data.
Before getting into the details of a networking standard like Ethernet, we must first understand some basic terms and classifications that describe and differentiate network technologies -- so let's get started!
How Internet Search Engines Work
The good news about the Internet and its most visible component, the World Wide Web, is that there are hundreds of millions of pages available, waiting to present information on an amazing variety of topics. The bad news about the Internet is that there are hundreds of millions of pages available, most of them titled according to the whim of their author, almost all of them sitting on servers with cryptic names. When you need to know about a particular subject, how do you know which pages to read? If you're like most people, you visit an Internet search engine.
Internet search engines are special sites on the Web that are designed to help people find information stored on other sites. There are differences in the ways various search engines work, but they all perform three basic tasks:
- They search the Internet -- or select pieces of the Internet -- based on important words.
- They keep an index of the words they find, and where they find them.
- They allow users to look for words or combinations of words found in that index.
Early search engines held an index of a few hundred thousand pages and documents, and received maybe one or two thousand inquiries each day. Today, a top search engine will index hundreds of millions of pages, and respond to tens of millions of queries per day. In this article, we'll tell you how these major tasks are performed, and how Internet search engines put the pieces together in order to let you find the information you need on the Web.
How Internet Infrastructure Works
One of the greatest things about the Internet is that nobody really owns it. It is a global collection of networks, both big and small. These networks connect together in many different ways to form the single entity that we know as the Internet. In fact, the very name comes from this idea of interconnected networks.
Since its beginning in 1969, the Internet has grown from four host computer systems to tens of millions. However, just because nobody owns the Internet, it doesn't mean it is not monitored and maintained in different ways. The Internet Society, a non-profit group established in 1992, oversees the formation of the policies and protocols that define how we use and interact with the Internet.
In this article, you will learn about the basic underlying structure of the Internet. You will learn about domain name servers, network access points and backbones. But first you will learn about how your computer connects to others.
Collision Detection
Carrier-sense multiple access gives us a good start in regulating our conversation, but there is one scenario we still need to address. Let’s go back to our dinner table analogy and imagine that there is a momentary lull in the conversation. You and I both have something we would like to add, and we both "sense the carrier" based on the silence, so we begin speaking at approximately the same time. In Ethernet terminology, a collision occurs when we both spoke at once.
In our conversation, we can handle this situation gracefully. We both hear the other speak at the same time we are speaking, so we can stop to give the other person a chance to go on. Ethernet nodes also listen to the medium while they transmit to ensure that they are the only station transmitting at that time. If the stations hear their own transmission returning in a garbled form, as would happen if some other station had begun to transmit its own message at the same time, then they know that a collision occurred. A single Ethernet segment is sometimes called a collision domain because no two stations on the segment can transmit at the same time without causing a collision. When stations detect a collision, they cease transmission, wait a random amount of time, and attempt to transmit when they again detect silence on the medium.
The random pause and retry is an important part of the protocol. If two stations collide when transmitting once, then both will need to transmit again. At the next appropriate chance to transmit, both stations involved with the previous collision will have data ready to transmit. If they transmitted again at the first opportunity, they would most likely collide again and again indefinitely. Instead, the random delay makes it unlikely that any two stations will collide more than a few times in a row.
How Computer Viruses Work
Computer viruses are mysterious and grab our attention. On the one hand, viruses show us how vulnerable we are. A properly engineered virus can have an amazing effect on the worldwide Internet. On the other hand, they show how sophisticated and interconnected human beings have become.
For example, the thing making big news right now is the Mydoom worm, which experts estimate infected approximately a quarter-million computers in a single day (Times Online). Back in March 1999, the Melissa virus was so powerful that it forced Microsoft and a number of other very large companies to completely turn off their e-mail systems until the virus could be contained. The ILOVEYOU virus in 2000 had a similarly devastating effect. That's pretty impressive when you consider that the Melissa and ILOVEYOU viruses are incredibly simple.
In this article, we will discuss viruses -- both "traditional" viruses and the newer e-mail viruses -- so that you can learn how they work and also understand how to protect yourself. Viruses in general are on the wane, but occasionally a person finds a new way to create one, and that's when they make the news.
42) Tell me about ntbackup type ?
1)normal backup
Backs up all selected files and marks each file as backed up.
2)copy backup
Backs up all selected files, but does not mark any as backed up.
3)Differential
Backs up selected files only if they have not been backed up, or have been changed, but does not mark any as backed up.
4)Incremental
Backs up selected files only if they have not been backed up , or have been changed , and marks them as backed up.
5)Daily
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Backs up only files which have been changed today, but
does not mark them as backed up.
43) Difference Regedit and regedt32
When Windows 95 came out, the registry was one of the big new features offered with that operating system. Instead of storing system and application configuration information in a whole slew of .INI files scattered across the hard drive, the registry moved all of that information into one place. Knowing how to plow through the registry is probably something any decent Windows NT/ Windows 2000 sysadmin should know about.
One of the not-very-well-explained quirks about editing the registry is that there are two tools available by default for doing this in NT and 2K: REGEDIT and REGEDT32. The two have some marked differences that need to be kept in mind.
REGEDIT is basically a copy of the original registry-editing utility found in Windows 95, and is kept around in other versions of Windows for the sake of backward compatibility. REGEDT32, on the other hand, was only shipped with NT, 2K and XP. The main difference between the two is that REGEDT32 allows you to set and clear permissions in the registry, while REGEDIT doesn't.
Each key in the registry in NT and 2K (and XP, of course) has an access control list or ACL -- in exactly the same manner that files and folders on an NTFS volume have ACLs. The reason for this applies as it does on files and folders: to allow or deny access to certain objects based on a given user's credentials. This way a given user could be provided access to one particular subtree of the registry, but not another.
To edit the permissions for a particular key in REGEDT32, right-click on the key in the left-hand pane and select Permissions. A dialog box similar to the kind used to set permissions on files and folders will come up. This lets you set basic or advanced permissions, and also set or reset the inheritability of those permissions on any subkeys of the key you're editing. You may need to clear permissions for a subkey if you are, for instance, trying to uninstall an application from another user account and need to purge the keys as an administrator to do it.
Windows NT 4.0 and Windows 2000
Regedit.exe
Regedit.exe is included with Windows NT 4.0 and Windows 2000 primarily for its search capability. You can use Regedit.exe to make changes in the Windows NT 4.0 and Windows 2000 registry, but you cannot use it to view or edit all functions or data types on Windows NT 4.0 and Windows 2000.
The following limitations exist in the Regedit.exe version that is included with Windows NT 4.0 and Windows 2000:
| • | You cannot set the security for registry keys. |
| • | You cannot view, edit, or search the value data types REG_EXPAND_SZ and REG_MULTI_SZ. If you try to view a REG_EXPAND_SZ value, Regedit.exe displays it as a binary data type. If you try to edit either of these data types, Regedit.exe saves it as REG_SZ, and the data type no longer performs its intended function. |
| • | You cannot save or restore keys as hive files. |
Microsoft recommends that you use Regedit.exe only for its search capabilities on a Windows NT 4.0-based or Windows 2000-based computer.
Regedt32.exe
Regedt32.exe is the configuration editor for Windows NT 4.0 and Windows 2000. Regedt32.exe is used tomodify the Windows NT configuration database, or the Windows NTregistry. This editor allows you to view or modify the Windows NT registry.The editor provides views of windows that represent sections of theregistry, named hives. Each window displays two sections. On the leftside, there are folders that represent registry keys. On the right side,there are the values associated with the selected registry key. Regedt32 isa powerful tool, and you must use it with extreme caution when you changeregistry values. Missing or incorrect values in the registry can make theWindows installation unusable.
Note Unlike Regedit.exe, Regedt32.exe does not support importing and exporting registration entries (.reg) files.
44) In which file the directory and information store is saved
edb - exchange database
Exchange Server is a complex beast, to say the least. It's just a fact of life that we can't escape and if one is to work with Exchange it's just best to accept it and move on. As easy as Exchange 2000 is to work with, it's still not the easiest or most pleasurable thing to do on a Saturday afternoon (or any day for that matter). Understanding the underlying processes and construction of Exchange can go a long way towards increasing your happiness factor-which is, after all, the only thing that really matters in life!
The Databases
Everything these days requires a database of some sort. The Internal Revenue Service, Active Directory, even the local supermarket-they all use a database. Databases are great, but they are not always easy to understand. Figure 1 shows an example of what the Exchange Server database looks like.
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Figure 1 - The current database (from Chapter 28 of the Exchange 2000 Server Resource Kit).
As you can see from Figure 1, there are actually three files that make up a current Exchange database for a storage group, as explained below.
<>· <>The .edb file contains all the folders, tables and indexes for messaging data and MAPI messages and attachments.
<>· <>The .stm file (new to Exchange 2000) contains Internet content in its native format.
<>· <>The .log files (transaction logs) maintains a record of every message stored in a storage group and provides fault tolerance in the event that a database must be restored. Exchange 2000 log files are always 5MB in size (5,252,880 bytes) and if not, then they are damaged. Each storage group also reserves to log files, Res1.log and Res2.log that are placeholders for extra disk place that can be used if the service runs out of space.
The Checkpoint File
In addition to the files previously mentioned, there is one other file of special note that plays a big role in keeping your Exchange Server database in order. The checkpoint file (edb.chk) tracks which entries in the transaction log files have already been recorded, and thus which ones will need to be replayed during a restoration situation. The checkpoint file thus speeds up recovery by telling the ESE exactly which log file entries need to be replayed and which do not-thus preventing extra writing during the restoration process.
Circular Logging
Typically, when a log file is filled, Exchange renames it and moves on to another, fresh log file. In this way, log files are not erased and thus continue to use space in 5MB increments. As the number of transactions grows, a set of log files is created. If a database fails, the transactions can be recovered by restoring the data from the log files. When circular logging is enabled, the first log file is overwritten and reused after the data that it contains has been written to the database. Circular logging is available to you, but is disabled by default. Should you enable circular logging, you cannot recover anything more recent than the last full backup. For this reason, circular logging is not normally recommended for use in a mission-critical production environment, with the possible exception of the Public folder that will house your NNTP news feeds, where log file sets are not required.
The Checksum
The concept of a checksum is not a new one. Checksums have been used for years to enable determination of file validity. Exchange Server makes use of checksums to verify the validity of the .edb files. Every .edb file is made up 4-KB pages and the integrity of each page is verified through a checksum and a 4-byte page number in the header of the database page. On each page in the database, the first 82 bytes contain the header information, which contains flags for the type of page and information about what kind of data the page contains. When the pages are read out of the database, they are compared for the correct page number and for the checksum. The checksum is calculated to ensure that the page being read is undamaged. If damage is detected, an error is returned, the database is stopped and an event is written in the to the event logs, thus ensuring that the database is operating with optimal integrity.
Other Important Files
Although not part of the actual Exchange database, the following two additional files may also be present on an Exchange Sever:
<>· <>The .srs files that permit backwards compatibility with Exchange 5.5 Server by emulating an Exchange 5.5 directory service. This will only be present if the Exchange ADC is installed and you then configure a Site Replication Server.
<>· <>The .kms files which provide security and encryption services. This will only be present on Exchange servers that have the KMS installed.
Yeah, But So What?
OK, so now we've got an idea of what makes up the Exchange Server databases and what special features they have. But who cares? What good does this do? Well:when I alluded earlier to working with Exchange on a Saturday afternoon, that seemed like a good time for the Exchange Server to crater and you find yourself in the midst of restoring it so that business can go on as normal on Monday. That's why you've got that pager after all, isn't it?
I discussed Exchange recovery in another article, Disaster Recovery, but I never really got into detail about setting up the backup system or how the restore action occurs.
Before we can get to the process of performing the backup, and more specifically, how Exchange handles a backup request, we need to understand what each type of backup will do for.
Backup Types
There are five basic types of backups that can be performed using ntbackup.exe, but only four of those apply to Exchange Server. They are summarized below:
<>· <>Full (normal) backups backup the entire Web Storage System and the Exchange log files. All transaction logs that contain transactions already committed to the database are deleted. Restoring from a full backup required only the full backup media. Full backups are the preferred means of backing up the Exchange databases.
<>· <>Copy backups act the same of full backups with the exception that the transaction log files are not deleted. You can perform a copy backup at any time without disturbing the status of any other type of backup.
<>· <>Incremental backups backup all log files prior to the checkpoint log and then delete them. Additionally, incremental backups back up all transaction log files and delete the log files that contain transactions that have been committed to the database. Restoring from an incremental backup requires that you have the last full backup and each subsequent incremental backup. If one incremental backup is damaged, you cannot restore any incremental backups made after that point as one damaged log file prevents replaying subsequent log files. It is critical that all incremental backups be restored prior to starting log file replay to prevent losing data or damaging the database.
<>· <>Differential backups backup all log files prior to the checkpoint file, but does not delete them. Due to this, each backup file will be larger in size than the previous file. Restoring from a differential backup requires that you have the last full backup and the last differential backup. Differential backups are the second most preferred method of performing backups, after full backups.
The Backup Process
When the backup process is started (using the ntbackup.exe), the Web Storage System informs the ESE that it is entering a backup mode and a patch file is created for each database in the backup (if for a full backup, otherwise a patch file is not created). The currently open log file is closed out and renames and new log file is opened at this time as well. This indicates the point at which the ESE can truncate the logs after the backup process has completed. Figure 2 illustrates the backup process.
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Figure 2 - The backup process (from Chapter 28 of the Exchange 2000 Server Resource Kit).
When the backup is started, the agent requests that the database read and sequence all database pages from the ESE. As the database reads the pages, the ESE verifies them through a checksum to ensure that they are valid. If they are invalid, the backup stops to prevent the storage of damaged data. After the backup is complete and all the pages are read, the backup copies the logs and patch files to the backup set. The log files are then truncated or deleted at the point when the new generation started at the beginning of the backup. The backup set closes, the ESE enters normal mode, and the backup is complete.
The preceding description assumed that you were performing an online backup (databases online at the time of backup), which is the preferred mode since it allows the databases to remain online and usable. You can, however, perform an offline backup by taking the databases offline. Offline backups are always full backups as the databases are dismounted and therefore not available for writing by network clients.
Of course, the backup is just the first half of the solution. Being able to restore the data would be nice as well.
The Restoration Process
The restoration process pretty much mirrors the backup process, but obviously in reverse. Before you can perform a restoration, you will need to take the database (or storage group) offline by dismounting it. When the restoration process begins, the ESE enters restore mode. The backup agent copies the database from the backup media to the target location. The associated log and patch files are copied to a temporary location (as specified by the backup operator) so they aren't saved to the same location as current files in the Exchange or Production Database directory. Should the log and patch files happen to be places in the same location, log files can be overwritten which will cause corruption of the database. After the files are restored, a special instance of the ESE starts for the specific purpose of restoring the database. It applies the patch file and log files to bring the database up to date. After the restore is complete, the log and patch files are deleted from the temporary location and the storage group is mounted and made available for use. Figure 3 summarizes the restoration process.
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Figure 3 - The restoration process (from Chapter 28 of the Exchange 2000 Server Resource Kit).
One Last Thing:
A point worth mentioning is that the version of ntbackup.exe that ships with Windows 2000 (5.0.2172.1) cannot be used to perform Exchange 2000 Server backups. You will need to have version 5.0.2195.1117 or later installed on your system. Figure 4 shows the version of ntbackup.exe that ships with Windows 2000 (unmodified) and Figure 5 shows the version that comes with Service Pack 2.
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Figure 4 - ntbackup.exe original file.
Figure 5 - ntbackup.exe in Service Pack 2.
Wrap-Up:
As we've seen, the Exchange Server database arrangement is a fairly complex one, although one that has safeguards built into it to minimize damage and prevent the use of damaged databases. The backup and restore processes are quite complex, although for the most part hidden away from us. The most important thing that I can leave you with is this: do not arbitrarily delete your transaction logs or checkpoint log-doing so may really, really screw up your weekend. Let Exchange and the backup process handle purging these files-its just better that way.
45) In which file mails are stored in outlook express and Netscape navigator
.dbx files in which Outlook Express stores folders and identifies e-Mails stored in them. A .dbx file is the proprietary database format in which Outlook Express stores the emails. If Outlook Express crashes and you cannot find a given dbx file or recover given message from the dbx file.
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