In networks, a jabber is any device that is handling electrical signals improperly, usually affecting the rest of the network. In an Ethernet network, devices compete for use of the line, attempting to send a signal and then retrying in the event that someone else tried at the same time. A jabber can look like a device that is always sending, effectively bringing the network to a halt. A jabber is usually the result of a bad network interface card (NIC). Occasionally, it can be caused by outside electrical interference.
 
 

Jitter is the deviation in or displacement of some aspect of the pulses in a high-frequency digitalsignal. As the name suggests, jitter can be thought of as shaky pulses. The deviation can be in terms of amplitude, phase timing, or the width of the signal pulse. Another definition is that it is "the period frequency displacement of the signal from its ideal location." Among the causes of jitter are electromagnetic interference (EMI) and crosstalk with other signals. Jitter can cause a display monitor to flicker; affect the ability of the processor in a personal computer to perform as intended; introduce clicks or other undesired effects in audio signals, and loss of transmitted data between network devices. The amount of allowable jitter depends greatly on the application.
 
 

On a local area network (LAN) or other network, the MAC (Media Access Control) address is your computer's unique hardware number. (On an Ethernet LAN, it's the same as your Ethernet address.) When you're connected to the Internet from your computer (or host as the Internet protocol thinks of it), a correspondence table relates your IP address to your computer's physical (MAC) address on the LAN.

The MAC address is used by the Media Access Control sublayer of the Data-Link Control (DLC) layer of telecommunication protocols. There is a different MAC sublayer for each physical device type. The other sublayer level in the DLC layer is the Logical Link Control sublayer.
 
 

The Master Boot Record (MBR) is the information in the first sector of any hard disk or diskette that identifies how and where an operating system is located so that it can be booted (loaded) into the computer's main storage or RAM. The Master Boot Record is also sometimes called the "partition sector" or the "master partition table" because it includes a table that locates each partition that the hard disk has been formatted into. In addition to this table, the MBR also includes a program that reads the boot sector record of the partition containing the operating system to be booted into RAM. In turn, that record contains a program that loads the rest of the operating system into RAM.
 
 

Multibank Dynamic RAM (MDRAM) is a type of video RAM, developed by MoSys, that divides memory into multiple 32 KB parts or "banks" that can be accessed individually. Traditional video RAM is monolithic; the entire frame buffer is accessed at one time. Having individual memory banks allows accesses to be interleaved concurrently, increasing overall performance. It's also cheaper since, unlike other forms of video RAM, cards can be manufactured with just the right amount of RAM for a given resolution capability instead of requiring it to be in multiples of megabytes.
 
 

The Microsoft Foundation Class (MFC) Library is a collection of classes (generalized definitions used in object-oriented programming) that can be used in building application programs. The classes in the MFC Library are written in the C++ programming language. The MFC Library saves a programmer time by providing code that has already been written. It also provides an overall framework for developing the application program.

There are MFC Library classes for all graphical user interface elements (windows, frames, menus, tool bars, status bars, and so forth), for building interfaces to databases, for handling events such as messages from other applications, for handling keyboard and mouse input, and for creating ActiveX controls.
 
 

Moore's Law is that the pace of microchip technology change is such that the amount of data storage that a microchip can hold doubles every year or at least every 18 months. In 1965 when preparing a talk, Gordon Moore noticed that up to that time microchip capacity seemed to double each year. The pace of change having slowed down a bit over the past few years, the definition has changed (with Gordon Moore's approval) to reflect that the doubling occurs only every 18 months.

In September, 1997, announcements by Intel of 2-bit flash memory and by IBM of chip circuitry of copper rather than aluminum suggested a return of the original version of Moore's Law.
 
 

MP3 (MPEG-1 Audio Layer-3) is a standard technology and format for compressing a sound sequence into a very small file (about one-twelfth the size of the original file) while preserving the original level of sound quality when it is played. MP3 files (identified with the file name suffix of ".mp3") are available for downloading from a number of Web sites. Many Windows 98 users will find that they have a player built into their operating system. Otherwise, you can download a player from one of several popular MP3 sites. MP3 files are usually download-and-play files rather than streaming sound files that you link-and-listen-to with RealPlayer and similar products (However, streaming MP3 is possible.) Winamp (PC), MacAmp (Mac), and mpeg123 (UNIX) are popular MP3 players, but there are many others. To create an MP3 file, you use a program called a ripper to get a selection from a CD onto your hard drive and another program called an encoder to convert the selection to an MP3 file. Most people, however, simply download MP3s from someone else and play them.

Digitalaudio is typically created by taking 16 bit samples a second of the analog signal. Since this signal is typically spread out over a spectrum of 44.1 thousand cycles per second (kHz), this means that one second of CD quality sound requires 1.4 million bits of data. Using their knowledge of how people actually perceive sound, the developers of MP3 devised a compression algorithm that reduces data about sound that most listeners can not perceive. MP3 is currently the most powerful algorithm in a series of audio encoding standards developed under the sponsorship of the Motion Picture Experts Group (MPEG) and formalized by the International Organization for Standardization (ISO).

Since it is relatively easy to create MP3 files from CD selections and make them available on Web sites for downloading, companies and sites that promote the MP3 format are sometimes accused of encouraging copyright violations. (It is illegal to copy music from a CD and redistribute it unless you have the copyright owner's permission.) On the other hand, MP3 enthusiasts claim that what CD publishers are afraid of is any kind of non-CD distribution. While there are several proposals for how to discourage such piracy, there is currently no secure distribution and copyright management standard that publishers and other parties agree upon.

Several Web sites are promoting MP3 as both a high-quality audio format and as a way in which self-publishers can gain ready access to an audience. Currently, some music publishers are providing sample cuts in the MP3 format as a way to entice users to buy a CD. However, not much mainstream copyrighted material is available except as an illegal download.

As an alternative approach to individual MP3 downloads, IBM and five recording companies plan to offer entire CD downloads to users with access to high-bandwidth cable modem service. Formerly called Madison, the service, which will be tested during 1999, will ensure royalty payment to the artists and publishers. The Recording Industry Association of America (RIAA) is also working on a Secure Digital Music Initiative (SDMI).
 
 

NAT (Network Address Translation) is the translation of an Internet Protocol address (IP address) used within one network to a different IP address known within another network. One network is designated the inside network and the other is the outside. Typically, a company maps its local inside network addresses to one or more global outside IP addresses and unmaps the global IP addresses on incoming packets back into local IP addresses. This helps ensure security since each outgoing or incoming request must go through a translation process that also offers the opportunity to qualify or authenticate the request or match it to a previous request. NAT also conserves on the number of global IP addresses that a company needs and it lets the company use a single IP address in its communication with the world.

NAT is included as part of a router and is often part of a corporate firewall. Network administrators create a NAT table that does the global-to-local and local-to-global IP address mapping. NAT can also be used in conjunction with policy routing. NAT can be statically defined or it can be set up to dynamically translate from and to a pool of IP addresses. Cisco's version of NAT lets an administrator create tables that map:

• A local IP address to one global IP address statically
• A local IP address to any of a rotating pool of global IP addresses that a company may have
• A local IP address plus a particular TCP port to a global IP address or one in a pool of them
• A global IP address to any of a pool of local IP addresses on a round-robin basis

NetBEUI (NetBIOS Extended User Interface) is a new, extended version of NetBIOS, the program that lets computers communicate within a local area network. NetBEUI (pronounced net-BOO-ee) formalizes the frame format (or arrangement of information in a data transmission) that was not specified as part of NetBIOS. NetBEUI was developed by IBM for its LAN Manager product and has been adopted by Microsoft for its Windows NT, LAN Manager, and Windows for Workgroups products. Hewlett-Packard and DEC use it in comparable products.

NetBEUI is the best performance choice for communication within a single LAN. Because, like NetBIOS, it does not support the routing of messages to other networks, its interface must be adapted to other protocols such as IPX or TCP/IP. A recommended method is to install both NetBEUI and TCP/IP in each computer and set the server up to use NetBEUI for communication within the LAN and TCP/IP for communication beyond the LAN.
 
 

NetBIOS (Network Basic Input/Output System) is a program that allows applications on different computers to communicate within a local area network (LAN). It was created by IBM for its early PC Network, was adopted by Microsoft, and has since become a de facto industry standard. NetBIOS is used in Ethernet, token ring, and Windows NT networks. It does not in itself support a routing mechanism so applications communicating on a wide area network (WAN) must use another "transport mechanism" (such as TCP) rather than or in addition to NetBIOS.

NetBIOS frees the application from having to understand the details of the network, including error recovery (in session mode). A NetBIOS request is provided in the form of a Network Control Block (NCB) which, among other things, specifies a message location and the name of a destination.

NetBIOS provides the session and transport services described in the Open Systems Interconnection (OSI) model. However, it does not provide a standard frame or data format for transmission. A standard frame format is provided in the NetBIOS Extended User Interface (NetBEUI).

NetBIOS provides two communication modes: session or datagram. Session mode lets two computers establish a connection for a "conversation," allows larger messages to be handled, and provides error detection and recovery. Datagram mode is "connectionless" (each message is sent independently), messages must be smaller, and the application is responsible for error detection and recovery. Datagram mode also supports the broadcast of a message to every computer on the LAN.
 
 

A network computer (NC) is a concept from Oracle and Sun Microsystems for a low-cost personal computer for business networks that, like the Net PC, would be configured with only essential equipment, devoid of CD-ROM players, diskette drives, and expansion slots, and intended to be managed and maintained centrally (any new software would be downloaded). Unlike the Net PC, the network computer could be based on microprocessors other than Intel's and might include a Java-base operating system rather than Windows.

Along with the Net PC, the network computer is sometimes referred to as a thin client.
 
 

The Network File System (NFS) is a client/serverapplication that lets a computer user view and optionally store and update files on a remote computer as though they were on the user's own computer. The user's system needs to have an NFS client and the other computer needs the NFS server. Both of them require that you also have TCP/IP installed since the NFS server and client use TCP/IP as the program that sends the files and updates back and forth. (However, the User Datagram Protocol, UDP, which comes with TCP/IP, is used instead of TCP with earlier versions of NFS.)

NFS was developed by Sun Microsystems and has been designated a file server standard. Its protocol uses the Remote Procedure Call (RPC) method of communication between computers. You can install NFS on Windows 95 and some other operating systems using products like Sun's Solstice Network Client.

Using NFS, the user or a system administrator can mount all or a portion of a file system (which is a portion of the hierarchical tree in any file directory and subdirectory, including the one you find on your PC or Mac). The portion of your file system that is mounted (designated as accessible) can be accessed with whatever privileges go with your access to each file (read-only or read-write).

NFS has been extended to the Internet with WebNFS, a product and proposed standard that is now part of Netscape's Communicator browser. WebNFS offers what Sun believes is a faster way to access Web pages and other Internet files.
 
 

In information technology, a neural network is a system of programs and data structures that approximates the operation of the human brain. A neural network usually involves a large number of processors operating in parallel, each with its own small sphere of knowledge and access to data in its local memory. Typically, a neural network is initially "trained" or fed large amounts of data and rules about data relationships (for example, "A grandfather is older than a person's father"). A program can then instruct the network how to behave in response to an external stimulus (for example, to input from a computer user who is interacting with the network) or can initiate activity on its own (within the limits of its access to the external world).

Neural networks often use principles of fuzzy logic to make determinations. Neural networks are sometimes described in terms of knowledge layers, with, in general, more complex networks having deeper layers. In feedforward systems, learned relationships about data can "feed forward" to higher layers of knowledge.

Current applications of neural networks include: oil exploration data analysis, weather prediction, the interpretation of nucleotide sequences in biology labs, and the exploration of models of thinking and consciousness. In his recent novel, Galatea 2.2, Richard Powers envisions a neural network (named "Helen") that could be taught to pass a comprehensive exam in English literature.
 
 

NeXT was a computer company formed by Steven Jobs, one of the founders of Apple Computer, and also the name of the advanced personal computer or workstation that the company developed and first offered in 1988. The NeXT computer was an industrial designer's triumph, a futuristic black cube with a high-resolution display, a graphical user interface, and an operating system called NeXTStep.

In 1993, the computer was taken off the market. Jobs offered the object-oriented components of NeXTStep as a proposed standard for a development environment called OpenStep. In 1996, Apple Computer bought what was now NeXT Software and hired Jobs to return to Apple and help run the company. In 1998, Apple continued to offer OpenStep as a development environment for object-oriented applications that will run on multiple platforms.
 
 

NEXT (near-end crosstalk) is an error condition that can occur when connectors are attached to twisted-pair cabling. NEXT is usually caused by crossed or crushed wire pairs. The error condition does not require that the wires be crushed so much that the conductors inside become exposed. Two conductors only need to be close enough so that the radiating signal from one of the wires can interfere with the signal traveling on the other. Most medium- to high-end cable testers are capable of testing for NEXT errors.

In order to certify a cable for Category 3 (CAT 3), the NEXT test must be performed in 1 Mhz steps from 1 Mhz to 16 MHz. Since the level of signal loss or interference can change with frequency, a range of frequencies must be used to certify that the cable is acceptable over the entire range. In order to certify a cable for Category 5 (CAT 5) use, the test frequency range must be extended up to 100 MHz. A 1 MHz frequency step should still be used. In both cases, you must test both ends of the cable. This is because NEXT occurs on the ends of the cable right where the connector is attached.

Simply using CAT 5 cables, connectors, and patch panels does not guarantee that a network will support 100 Mb operation. You must actually certify your network for use at this speed with a CAT 5 cable tester after the network is fully installed.
 
 

NTFS (NT file system) is the system that the Windows NT operating system uses for storing and retrieving files on a hard disk. NTFS is the Windows NT equivalent of the Windows 95 FAT (file allocation table) and the OS/2 HPFS (high performance file system). However, NTFS offers a number of improvements over FAT and HPFS in terms of performance, extendability, and security.

Notable features of NTFS include:

• Use of a b-tree directory scheme to keep track of file clusters
• Information about a file's clusters and other data is stored with each cluster, not just a governing table (as FAT is)
• Support for very large files (up to 2 to the 64th power or approximately 16 billion billion bytes in size)
• An access control list (ACL) that lets a server administrator control who can access specific files
• Integrated file compression
• Support for names based on Unicode
• Support for long file names as well as "8 by 3" names
• Data security on both removable and fixed disks

How NTFS Works

The selection of the cluster size is a trade-off between efficient use of disk space and the number of disk accesses required to access a file. In general, using NTFS, the larger the hard disk the larger the default cluster size, since it's assumed that a system user will prefer to increase performance (fewer disk accesses) at the expense of some amount of space inefficiency.

When a file is created using NTFS, a record about the file is created in a special file, the Master File Table (MFT). The record is used to locate a file's possibly scattered clusters. NTFS tries to find contiguous storage space that will will hold the entire file (all of its clusters).

Each file contains, along with its data content, a description of its attributes (its metadata).
 
 

Object-oriented programming (OOP, for short) is a revolutionary new way of looking at computer programming. Historically, programs have been viewed as procedures (or we may think of these as "verbs") that operate on data. OOP takes the view that programs should start by thinking about the data (or "nouns") first. After all, the primary purpose of computing is the result...not the computing procedure itself. By using data modeling concepts and techniques, a programmer can identify data objects and their relationships. A generalization of a data object along with its possible data variables and methods (what to do with the variables) is a class of data objects. A real instance of a class is an object. (It's what you run in the computer.)

Some of the ideas and advantages of OOP include:

• The concept of a data class makes it possible to define subclasses of data objects that share some or all of the main class characteristics. Called inheritance, this property of OOP forces a more thorough data analysis, reduces development time, and ensures more accurate coding.
• Data hiding is possible because an object and its methods will know only about the data they need to know about. Because other objects and methods in the application program cannot be accessed without rewriting the object, the possiblities of accidental or unintended data corruption that are possible in procedural programs are not possible with OOP.
• The definition of a class is reuseable not only by the program for which it is initially created but also by other object-oriented programs (and, for this reason, can be more easily distributed for use in networks).
• The concept of data classes allows a programmer to create new data types that are not defined in the language itself.

OLE (Object Linking and Embedding) is Microsoft's framework for a compound document technology. Briefly, a compound document is something like a display desktop that can contain visual and information objects of all kinds: text, calendars, animations, sound, motion video, 3-D, continually updated news, controls, and so forth. Each desktop object is an independent program entity that can interact with a user and also communicate with other objects on the desktop. Part of Microsoft's ActiveX technologies, OLE takes advantage and is part of a larger, more general concept, the Component Object Model (COM) and its distributed version, DCOM). An OLE object is necessarily also a component (or COM object).
 
 

Packet-switched describes the type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. Breaking communication down into packets allows the same data path to be shared among many users in the network. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching and the Internet is basically a connectionless network.

Contrasted with packet-switched is circuit-switched, a type of network such as the regular voice telephone network in which the communication circuit (path) for the call is set up and dedicated to the participants in that call. For the duration of the connection, all resources on that circuit are unavailable for other users. Voice calls using the Internet's packet-switched system are possible. Each end of the conversation is broken down into packets that are reassembled at the other end.

Another common type of digital network that uses packet-switching is the X.25 network, a widely installed commercial wide area network protocol. Internet protocol packets can be carried on an X.25 network. The X.25 network can also support virtual circuits in which a logical connection is established for two parties on a dedicated basis for some duration. A permanent virtual circuit (PVC) reserves the path on an ongoing basis and is an alternative for corporations to a system of leased lines. A permanent virtual circuit is a dedicated logical connection but the actual physical resources can be shared among multiple logical connections or users.
 
 

Ping is a basic Internet program that lets you verify that a particular Internet address exists and can accept requests. The verb ping means the act of using the ping utility or command. Ping is used diagnostically to ensure that a host computer you are trying to reach is actually operating. If, for example, a user can't ping a host, then the user will be unable to use the File Transfer Protocol (FTP) to send files to that host. Ping can also be used with a host that is operating to see how long it takes to get a response back. Using ping, you can learn the number form of the IP address from the symbolic domain name.

Loosely, ping means "to get the attention of" or "to check for the presence of" another party online. Ping operates by sending a packet to a designated address and waiting for a response. The computer acronym was contrived to match the submariners' term for the sound of a returned sonar pulse.

Ping can also refer to the process of sending a message to all the members of a mailing list requesting an ACK (acknowledgement code). This is done before sending e-mail in order to confirm that all of the addresses are reachable.
 
 

A POP (point-of-presence) is the location of an access point to the Internet. A POP necessarily has a unique Internet (IP) address. Your Internet service provider (ISP) or online service provider (OSP) has a point-of-presence on the Internet. The number of POPs that an ISP or OSP has is sometimes used as a measure of its size or growth rate.

A POP may actually reside in rented space owned by the telecommunications carrier such as AT&T or Sprint to which the ISP is connected. A POP usually includes routers, digital/analog call aggregators, servers, and frequently frame relay or ATM switches.
 
 

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. POP3 is built into the Netmanage suite of Internet products and one of the most popular e-mail products, Eudora. It's also built into the Netscape and Microsoft Internet Explorer browsers.

An alternative protocol is IMAP (Interactive Mail Access Protocol). With IMAP, you view your e-mail at the server as though it was on your client computer. An e-mail message deleted locally is still on the server. E-mail can be kept on and searched at the server.

POP can be thought of as a "store-and-forward" service. 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.
 
 

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 TCP and UDP, 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 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 usual 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 addresses. 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.
 
 

On a Web server or HTTPD (Hypertext Transport Protocol daemon), port 80 is the port that the server "listens to" or expects to receive from a Web client, assuming that the default was taken when the server was configured or set up. A port can be specified in the range from 0-65536 on the NCSA server. However, the server administrator configures the server so that only one port number can be recognized. By default, the port number for a Web server is 80. Experimental services may sometimes be run at port 8080.
 
 

PowerPC is a microprocessorarchitecture, developed jointly by Apple, IBM, and Motorola, that uses reduced instruction-set computing (RISC). The PowerPC chip is used principally in IBM's RS/6000 workstations with its UNIX-based operating system, AIX, and in Apple Computer's Macintosh personal computers with their Mac OS operating system. The three developing companies, calling themselves the PowerPC Alliance, have made the PowerPC architecture an open standard, inviting other companies to build the architecture further.

The PowerPC architecture provides an alternative for any computer maker to the extremely popular processor architectures from Intel, including the Pentium's PC architecture. Microsoft builds its Windows line of operating systems to run on Intel processors (and this widely-sold combination is sometimes known as "Wintel".)

Developed at IBM, reduced instruction-set computing (RISC) is based on studies showing that the simpler computer instructions are the ones most frequently performed. Traditionally, processors have been designed to accommodate the more complex instructions as well. RISC performs the more complex instructions using combinations of simple instructions. The timing for the processor can then be based on simpler and faster operations, enabling the microprocessor to perform more instructions for a given clock speed. Typically, the PowerPC can perform one instruction for each clock cycle. The PowerPC architecture handles 32-bit instructions.

The PowerPC architecture is used to build several microprocessors:

• The 603e, intended for the more typical notebook and desktop user, with a 250 MHz clock speed
• The 604e, for systems providing multimedia applications, including the Macintosh PowerPC Platform line. The 604e is described as being for "power users." It provides floating-point capability and can process up to four instructions simultaneously. It comes in clock speeds up to 375 MHz.
• The copper-based 750 (marketed as the G3 for Apple's iMac and Power Macintosh computers), intended for the mainstream "notebook, mobile, and power-conscious desktop computing" market. The 750 has an L2cache controller built into it and operates in versions up to 400 MHz. A 500 MHz version is planned.

PPP (Point-to-Point Protocol) is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. For example, your Internet server provider may provide you with a PPP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. PPP uses the Internet protocol (IP) (and is designed to handle others). It is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) service. Essentially, it packages your computer's TCP/IP packets and forwards them to the server where they can actually be put on the Internet.

PPP is a full-duplex protocol that can be used on various physical media, including twisted pair or fiber optic lines or satellite transmission. It uses a variation of High Speed Data Link Control (HDLC) for packet encapsulation.

PPP is usually preferred over the earlier de facto standard Serial Line Internet Protocol (SLIP) because it can handle synchronous as well as asynchronous communication. PPP can share a line with other users and it has error detection that SLIP lacks. Where a choice is possible, PPP is preferred.
 
 

A PSN (processor serial number) is a software-readable unique serial number that Intel has stamped into its Pentium IIImicroprocessors. Intel offers this as a feature that can be optionally used to provide certain network management and e-commerce benefits. Basically, it lets a program identify individual PCs.

Pentiums are not the the first processors to be shipped with software-readable serial numbers. Sun RISC chips have, for many years, shipped with serial numbers, and it is a commonplace for software keys for applications software to be generated with reference to the processor ID, to provide a mechanism for copyright protection. However, Intel's PSN has caused concern to privacy advocates, on grounds that it may undercut individual user efforts to maintain their anonymity, especially when using the Internet. There is a concern that Web pages could covertly acquire PSNs which, if matched with user identities disclosed through a registration process, would facilitate detailed monitoring of the use of the Internet by the individual. For example, chat rooms could use PSNs to prevent unwelcome users from posting.

Reacting to the objections, Intel announced that they would ship Pentium IIIs with the PSN function turned off. However, since the function appears to be software-configurable without need for a reboot, this assurance seems to be of little comfort.
 
 

In an enterprise that uses the Internet, a proxy server is a server that acts as an intermediary between a workstation user and the Internet so that the enterprise can ensure security, administrative control, and caching service. A proxy server is associated with or part of a gateway server that separates the enterprise network from the outside network and a firewall server that protects the enterprise network from outside intrusion.

A proxy server receives a request for an Internet service (such as a Web page request) from a user. If it passes filtering requirements, the proxy server, assuming it is also a cache server, looks in its local cache of previously downloaded Web pages. If it finds the page, it returns it to the user without needing to forward the request to the Internet. If the page is not in the cache, the proxy server, acting as a client on behalf of the user, uses one of its own IP addresses to request the page from the server out on the Internet. When the page is returned, the proxy server relates it to the original request and forwards it on to the user.

To the user, the proxy server is invisible; all Internet requests and returned responses appear to be directly with the addressed Internet server. (The proxy is not quite invisible; its IP address has to be specified as a configuration option to the browser or other protocol program.)

An advantage of a proxy server is that its cache can serve all users. If one or more Internet sites are frequently requested, these are likely to be in the proxy's cache, which will improve user response time. In fact, there are special servers called cache servers. A proxy can also do logging.

The functions of proxy, firewall, and caching can be in separate server programs or combined in a single package. Different server programs can be in different computers. For example, a proxy server may in the same machine with a firewall server or it may be on a separate server and forward requests through the firewall.