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Definitions & Terms

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Fast Ethernet:

  • Fast Ethernet is a local area network (LAN ) transmission standard that provides a data rate of 100 megabits per second (referred to as "100BASE-T"). Workstations with existing 10 megabit per second (10BASE-T) Ethernet card can be connected to a Fast Ethernet network. (The 100 megabits per second is a shared data rate; input to each workstation is constrained by the 10 Mbps card.)

Fast Packet Technology:

  • In data transmission, a fast packet is one that is transmitted without any error checking at points along the route. Assurance that the packet arrived without error is the responsibility of the receiver. Fast packet transmission is possible because of the extremely low incidence of error or data loss on fiber optic media and is a characteristic of high bandwidth transmission technologies such as ATM.

FAT16/32 - File Alocation Table:

  • See File Alocation Table.

FDDI - Fiber Distributed Data Interface:

  • See Fiber Distributed Data Interface.

FDM - Frequency Division Multiplexing:

  • See Frequency Division Multiplexing.

Fermat Prime:

  • A Fermat prime is a Fermat number that is also a prime number. A Fermat number Fn is of the form 2m + 1, where m is the nth power of 2 (that is, m = 2n, where n is an integer). To find the Fermat number Fn for an integer n, you first find m = 2n, and then calculate 2m + 1. The term arises from the name of a 17th-Century French lawyer and mathematician, Pierre de Fermat, who first defined these numbers and noticed their significance.
  • Fermat believed that all numbers of the above form are prime numbers; that is, that Fn is prime for all integral values of n. This is indeed the case for n = 0, n = 1, n = 2, n = 3, and n = 4:
  • When n = 0, m = 20 = 1; therefore F0 = 21 + 1 = 2 + 1 = 3, which is prime
  • When n = 1,? m = 21 = 2; therefore F1 = 22 + 1 = 4 + 1 = 5, which is prime
  • When n = 2, m = 22 = 4; therefore F2 = 24 + 1 = 16 + 1 = 17, which is prime
  • When n = 3, m = 23 = 8; therefore F3 = 28 + 1 = 256 + 1 = 257, which is prime
  • When n = 4, m = 24 = 16; therefore F4 = 216 + 1 = 65536 + 1 = 65537, which is prime
  • Using computers, mathematicians have not yet found any Fermat primes for n greater than 4. So far, Fermat's original hypothesis seems to have been wrong. The search continues for Fermat numbers Fn that are prime when n is greater than 4.

Fermat's Last Theorem:

  • Fermat's Last Theorem (FLT), a significant hypothesis in number theory , was first stated by Pierre de Fermat, a 17th-Century laywer and amateur mathematician. The proposition was discovered by his son Samuel while collecting and organizing the elder Fermat's papers and letters posthumously.
  • The proposition is as follows. Suppose we have the following equation:
  • xn + yn = zn
  • where x, y, and z are nonzero integers. Then the equation has no solution for integers n larger than 2.
  • Fermat did not state a proof of this hypothesis, although he said that he had found a remarkable demonstration but did not have space in the margin of his text to write it down. Mathematicians immediately began seeking a proof. (Many mathematicians today doubt that Fermat had actually found a valid proof.) The hypothesis was demonstrated true for increasingly large values of n, but proving the theorem in general, for all integers n greater than 2, remained elusive for centuries.
  • Two strategies of proof can reasonably be tried. First, one can assume that the equation has a solution for some nonzero integers x, y, and z, and for some n greater than 2, and then derive a contradiction from this assumption. This tactic is formally known as reductio ad absurdum. Second, one might prove that the equation has no solution for n = 3, and then demonstrate that if the equation has no solution for n = k, where k is an unspecified integer, then there exists no solution for n = k + 1. This is the technique of mathematical induction.
  • In the 1990s, the British mathematician Andrew Wiles produced a proof of FLT that, after some refinements, has withstood all challenges to date.

FC - Fibre Channel:

  • See Fibre Channel.

FC-AL - Fibre Channel Abitrary Loop:

  • See Fibre Channel.

FC-IP - Fibre Channel over IP:

  • See Fibre Channel over IP.

Fibre Channel - FC:

  • Fibre Channel is a technology for transmitting data between computer devices at a data rate of up to 1 Gbps , or one billion bits per second. (A data rate of 10 Gbps has been proposed by the Fibre Channel Industry Association.) Fibre Channel is especially suited for connecting computer server s to shared storage devices and for interconnecting storage controllers and drives. Since Fibre Channel is three times as fast, it has begun to replace the Small Computer System Interface (SCSI ) as the transmission interface between servers and clustered storage devices. Fibre channel is more flexible; devices can be as far as ten kilometers (about six miles) apart if optical fiber is used as the physical medium. Optical fiber is not required for shorter distances, however, because Fibre Channel also works using coaxial cable and ordinary telephone twisted pair.
  • Fibre Channel offers point-to-point, switched, and loop interfaces. It is designed to interoperate with SCSI, the Internet Protocol (IP ) and other protocols, but has been criticized for its lack of compatibility - primarily because (like in the early days of SCSI technology) manufacturers sometimes interpret specifications differently and vary their implementations. Standards for Fibre Channel are specified by the Fibre Channel Physical and Signalling standard, and the ANSI X3.230-1994, which is also ISO 14165-1.

Fibre Channel over IP:

  • Fibre Channel over IP (FCIP or FC/IP, also known as Fibre Channel tunneling or storage tunneling) is an Internet Protocol (IP)-based storage networking technology developed by the Internet Engineering Task Force (IETF). FCIP mechanisms enable the transmission of Fibre Channel (FC) information by tunneling data between storage area network (SAN ) facilities over IP networks; this capacity facilitates data sharing over a geographically distributed enterprise. One of two main approaches to storage data transmission over IP networks, FCIP is among the key technologies expected to help bring about rapid development of the storage area network market by increasing the capabilities and performance of storage data transmission.
  • FCIP Versus iSCSI
  • The other method, iSCSI, generates SCSI codes from user requests and encapsulates the data into IP packets for transmission over an Ethernet connection. Intended to link geographically distributed SANs, FCIP can only be used in conjunction with Fibre Channel technology; in comparison, iSCSI can run over existing Ethernet networks. SAN connectivity, through methods such as FCIP and iSCSI, offers benefits over the traditional point-to-point connections of earlier data storage systems, such as higher performance, availability, and fault-tolerance. A number of vendors, including Cisco, Nortel, and Lucent have introduced FCIP-based products (such as switches and routers). A hybrid technology called Internet Fibre Channel Protocol (iFCP) is an adaptation of FCIP that is used to move Fibre Channel data over IP networks using the iSCSI protocols.

Fiber Distributed Data Interface - FDDI:

  • Fiber Distributed Data Interface (FDDI) is a set of ANSI and ISO standards for data transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users. FDDI is frequently used on the backbone for a wide area network (WAN).
  • An FDDI network contains two token rings, one for possible backup in case the primary ring fails. The primary ring offers up to 100 Mbps capacity. If the secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps. The single ring can extend the maximum distance; a dual ring can extend 100 km (62 miles).
  • FDDI is a product of American National Standards Committee X3-T9 and conforms to the Open Systems Interconnection (OSI ) model of functional layering. It can be used to interconnect LANs using other protocols. FDDI-II is a version of FDDI that adds the capability to add circuit-switched service to the network so that voice signals can also be handled. Work is underway to connect FDDI networks to the developing Synchronous Optical Network (SONET).

Fiber Optics:

  • Fiber optic (or "optical fiber") refers to the medium and the technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber. Fiber optic wire carries much more information than conventional copper wire and is far less subject to electromagnetic interference. Most telephone company long-distance lines are now fiber optic.
  • Transmission on fiber optic wire requires repeating at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have fiber optic wires or cables from the phone company's branch office to local customers (known as local loop).

Field Programmable Gate Array - FPGA:

  • A Field Programmable Gate Array (FPGA) is an integrated circuit (IC ) that can be programmed in the field after manufacture. FPGAs are similar in principle to, but have vastly wider potential application than, programmable read-only memory (PROM ) chips. FPGAs are used by engineers in the design of specialized ICs that can later be produced hard-wired in large quantities for distribution to computer manufacturers and end users. Ultimately, FPGAs might allow computer users to tailor microprocessors to meet their own individual needs.

File Alocation Table - FAT16/32:

  • A File Allocation Table (FAT) is a table that an operating system maintains on a hard disk that provides a map of the cluster s (the basic units of logical storage on a hard disk) that a file has been stored in. When you write a new file to a hard disk, the file is stored in one or more clusters that are not necessarily next to each other; they may be rather widely scattered over the disk. A typical cluster size is 2,048 byte s, 4,096 bytes, or 8,192 bytes. The operating system creates a FAT entry for the new file that records where each cluster is located and their sequential order. When you read a file, the operating system reassembles the file from clusters and places it as an entire file where you want to read it. For example, if this is a long Web page, it may very well be stored on more than one cluster on your hard disk.
  • Until Windows 95 OSR2 (OEM Release 2), DOS and Windows file allocation table entries were 16 bits in length, limiting hard disk size to 128 megabyte s, assuming a 2,048 size cluster. Up to 512 megabyte support is possible assuming a cluster size of 8,192 but at the cost of using clusters inefficiently. DOS 5.0 and later versions provide for support of hard disks up to two gigabytes with the 16-bit FAT entry limit by supporting separate FATs for up to four partitions.
  • With 32-bit FAT entry (FAT32) support in Windows 95 OSR2, the largest size hard disk that can be supported is two terabytes! However, personal computer users are more likely to take advantage of FAT32 with 5 or 10 gigabyte drives. Also see: fat Mac and Virtual File Allocation Table.

File System:

  • 1) In a computer, a file system is the way in which file s are named and where they are placed logically for storage and retrieval. The DOS, Windows, OS/2, Macintosh, and UNIX-based operating systems all have file systems in which files are placed somewhere in a hierarchical (tree) structure. A file is placed in a directory (folder in Windows) or subdirectory at the desired place in the tree structure.
  • File systems specify conventions for naming files. These conventions include the maximum number of characters in a name, which characters can be used, and, in some systems, how long the file name suffix can be. A file system also includes a format for specifying the path to a file through the structure of directories.
  • 2) Sometimes the term refers to the part of an operating system or an added-on program that supports a file system as defined in (1). Examples of such add-on file systems include the Network File System (NFS) and the Andrew file system (AFS).

File Transfer Protocol - FTP:

  • File Transfer Protocol (FTP), a standard Internet protocol, is the simplest way to exchange files between computers on the Internet. Like the Hypertext Transfer Protocol (HTTP), which transfers displayable Web pages and related files, and the Simple Mail Transfer Protocol (SMTP), which transfers e-mail, FTP is an application protocol that uses the Internet's TCP/IP protocols. FTP is commonly used to transfer Web page files from their creator to the computer that acts as their server for everyone on the Internet. It's also commonly used to download programs and other files to your computer from other servers.
  • As a user, you can use FTP with a simple command line interface (for example, from the Windows MS-DOS Prompt window) or with a commercial program that offers a graphical user interface. Your Web browser can also make FTP requests to download programs you select from a Web page. Using FTP, you can also update (delete, rename, move, and copy) files at a server. You need to logon to an FTP server. However, publicly available files are easily accessed using anonymous FTP.
  • Basic FTP support is usually provided as part of a suite of programs that come with TCP/IP. However, any FTP client program with a graphical user interface usually must be downloaded from the company that makes it.


  • A firewall is a set of related programs, located at a network gateway server , that protects the resources of a private network from users from other networks. (The term also implies the security policy that is used with the programs.) An enterprise with an intranet that allows its workers access to the wider Internet installs a firewall to prevent outsiders from accessing its own private data resources and for controlling what outside resources its own users have access to.
  • Basically, a firewall, working closely with a router program, examines each network packet to determine whether to forward it toward its destination. A firewall also includes or works with a proxy server that makes network requests on behalf of workstation users. A firewall is often installed in a specially designated computer separate from the rest of the network so that no incoming request can get directly at private network resources.
  • There are a number of firewall screening methods. A simple one is to screen requests to make sure they come from acceptable (previously identified) domain name and Internet Protocol addresses. For mobile users, firewalls allow remote access in to the private network by the use of secure logon procedures and authentication certificates. A number of companies make firewall products. Features include logging and reporting, automatic alarms at given thresholds of attack, and a graphical user interface for controlling the firewall.


  • See IEEE 1394.


  • See Sequential Logic.

Floating Point Unit - FPU:

  • A floating point unit (FPU), also known as a numeric coprocessor, is a microprocessor or special circuitry in a more general microprocessor that manipulates numbers more quickly than the basic microprocessor your computer uses. It does so by having a special set of instructions that focus entirely on large mathematical operations. A floating point unit is often built into today's personal computers, but it is needed only for special applications such as graphic image processing or display. Personal computers that don't have floating point units can sometimes handle software that requires them by installing a floating point emulator.
  • Floating point numbers are numbers that are carried out to a certain decimal position (such as 2.17986). They are stored in three parts: the sign (plus or minus), the significant or mantissa which is the digits that are meaningful, and the exponent or order of magnititude of the significant, which determines the place to which the decimal point floats. Floating point numbers are binary (expressed in powers of 2).
  • Some software you might download from the World Wide Web, such as Macromedia's Shockwave , may require that your computer have a floating point unit. If it doesn't, you may be able to download an FPU emulator that will fool the software into thinking you have one.

FPGA - Field Programmable Gate Array:

  • See Field Programmable Gate Array.

FPU - Floating Point Unit:

  • See Floating Point Unit.

Fractional T-1:

  • A fractional T-1 or T-3 line is a T-1 or T-3 digital phone line in the North American T-carrier system that is leased to a customer at a fraction of its data-carrying capacity and at a correspondingly lower cost. A T-1 line contains 24 channels, each with a data transfer capacity of 64 Kbps . The customer can rent some number of the 24 channels. The transmission method and speed of transfer remain the same. Overhead bits and framing are still used, but the unrented channels simply contain no data.
  • T-3 lines (which offer 672 64 Kbps channels) are also sometimes offered as a fractional service. T-1 and fractional T-1 service are sometimes advertised as "point-to-point" service (from the customer to the service provider).

Frame Relay:

  • Frame relay is a telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the end-points, which speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC ), which means that the customer sees a continous, dedicated connection without having to pay for a full-time leased line, while the service provider figures out the route each frame travels to its destination and can charge based on usage. An enterprise can select a level of service quality - prioritizing some frames and making others less important. Frame relay is offered by a number of service providers, including AT&T. Frame relay is provided on fractional T-1 or full T-carrier system carriers. Frame relay complements and provides a mid-range service between ISDN, which offers bandwidth at 128 Kbps, and Asynchronous Transfer Mode (ATM), which operates in somewhat similar fashion to frame relay but at speeds from 155.520 Mbps or 622.080 Mbps.
  • Frame relay is based on the older X.25 packet-switching technology which was designed for transmitting analog data such as voice conversations. Unlike X.25 which was designed for analog signals, frame relay is a fast packet technology , which means that the protocol does not attempt to correct errors. When an error is detected in a frame, it is simply "dropped." (thrown away). The end points are responsible for detecting and retransmitting dropped frames. (However, the incidence of error in digital networks is extraordinarily small relative to analog networks.)
  • Frame relay is often used to connect local area networks with major backbones as well as on public wide area networks and also in private network environments with leased lines over T-1 lines. . It requires a dedicated connection during the transmission period. It's not ideally suited for voice or video transmission, which requires a steady flow of transmissions. However, under certain circumstances, it is used for voice and video transmission.
  • Frame relay relays packets at the Data Link layer of the Open Systems Interconnection (OSI) model rather than at the Network layer. A frame can incorporate packets from different protocols such as Ethernet and X.25. It is variable in size and can be as large as a thousand bytes or more.


Frequency Division Multiplexing - FDM:

  • Frequency-division multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is assigned a different frequency (subchannel) within the main channel.
  • A typical analog Internet connection via a twisted pair telephone line requires approximately three kilohertz (3 kHz) of bandwidth for accurate and reliable data transfer. Twisted-pair lines are common in households and small businesses. But major telephone cables, operating between large businesses, government agencies, and municipalities, are capable of much larger bandwidths.
  • Suppose a long-distance cable is available with a bandwidth allotment of three megahertz (3 MHz). This is 3,000 kHz, so in theory, it is possible to place 1,000 signals, each 3 kHz wide, into the long-distance channel. The circuit that does this is known as a multiplexer. It accepts the input from each individual end user, and generates a signal on a different frequency for each of the inputs. This results in a high-bandwidth, complex signal containing data from all the end users. At the other end of the long-distance cable, the individual signals are separated out by means of a circuit called a demultiplexer, and routed to the proper end users. A two-way communications circuit requires a multiplexer/demultiplexer at each end of the long-distance, high-bandwidth cable.
  • When FDM is used in a communications network, each input signal is sent and received at maximum speed at all times. This is its chief asset. However, if many signals must be sent along a single long-distance line, the necessary bandwidth is large, and careful engineering is required to ensure that the system will perform properly. In some systems, a different scheme, known as Time-Division Multiplexing, is used instead.

FTP - File Transfer Protocol:

  • See File Trasfer Protocol.

Full Duplex:

  • Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. For example, on a local area network with a technology that has full-duplex transmission, one workstation can be sending data on the line while another workstation is receiving data. Full-duplex transmission necessarily implies a bidirectional line (one that can move data in both directions).


  • In information technology, the term function (pronounced FUHNK-shun) has a number of meanings. It's taken from the Latin "functio" - to perform.
  • 1) In its most general use, a function is what a given entity does in being what it is.
  • 2) In C language and other programming, a function is a named procedure that performs a distinct service. The language statement that requests the function is called a function call. Programming languages usually come with a compiler and a set of "canned" functions that a programmer can specify by writing language statements. These provided functions are sometimes referred to as library routines. Some functions are self-sufficient and can return results to the requesting program without help. Other functions need to make requests of the operating system in order to perform their work.
  • 3) In mathematics, a function is an association between two sets of values in which each element of one set has one assigned element in the other set so that any element selected becomes the independent variable and its associated element is the dependent variable. Thus, in:
  • y = f(x)
  • y is said to be a function of x.
  • 4) In a hardware device, a function is one complete physical movement that has a discernible consequence relative to the device's purposes. In a printer, for example, this might be a carriage return or a line feed.

Fuzzy Logic:

  • Fuzzy logic is an approach to computing based on "degrees of truth" rather than the usual "true or false" (1 or 0) Boolean logic on which the modern computer is based. The idea of fuzzy logic was first advanced by Dr. Lotfi Zadeh of the University of California at Berkeley in the 1960s. Dr. Zadeh was working on the problem of computer understanding of natural language. Natural language (like most other activities in life and indeed the universe) is not easily translated into the absolute terms of 0 and 1. (Whether everything is ultimately describable in binary terms is a philosophical question worth pursuing, but in practice much data we might want to feed a computer is in some state in between and so, frequently, are the results of computing.)
  • Fuzzy logic includes 0 and 1 as extreme cases of truth (or "the state of matters" or "fact") but also includes the various states of truth in between so that, for example, the result of a comparison between two things could be not "tall" or "short" but ".38 of tallness."
  • Fuzzy logic seems closer to the way our brains work. We aggregate data and form a number of partial truths which we aggregate further into higher truths which in turn, when certain thresholds are exceeded, cause certain further results such as motor reaction. A similar kind of process is used in artificial computer neural network and expert systems. It may help to see fuzzy logic as the way reasoning really works and binary or Boolean logic is simply a special case of it.


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