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Frequency: A characteristic of an electrical or electronic signal which describes the periodic recurrence of cycles. Frequency is
inversely proportional to the wavelength or pulse width of the signal (i.e., long wavelength signals have low frequencies and short
wavelength signals yield high frequencies).
Full-duplex: A method of transmitting and receiving data simultaneously over a single pair of wires. Compare with Half-Duplex.
G
H
Half-Duplex: The transmission of data in both directions, but only one direction at a time. Compare with Full-Duplex.
Handshaking: A process that two modems go through at the time of call setup to establish synchronization over the data communica-
tions link. It is a synchronization and negotiation process accomplished by the exchange of predefined, mutually recognized control
codes.
Hard Disk: A metal disk covered with magnetic recording material. Some can hold up to several hundred megabytes of information.
Contrast with floppy disk.
Hardware: The equipment that makes up your computer system, including the keyboard, mouse, disk drives and monitor.
Hexadecimal: A base 16 numbering system used to represent binary values. Hex uses the numbers 0-9 and the letters A-F: usually
notated by an "h" (e.g., "4CF h", read "four charley fox, hex"). The result is that one hex digit represents a 4-bit value.
Host: The computer that is designated as retaining information or processing power to service the needs of other computers or
terminals. Mainframes and mid-range computers are hosts; however, with today's powerful microprocessors, PCs can also be config-
ured to serve as hosts. Often, a PC on a LAN will be set up as a host to provide LAN access for remote users.
I
Initialize: To start anew and establish start-up parameters, typically involves clearing all or some part of the device's memory or disk
space.
Interface: A common meeting ground supplied by hardware or software to facilitate a compatible connection and operation between
two devices or programs. For example, when two PCs are connected, they use a common interface across the physical connectors, so
that the signals being sent and received are accurately interpreted. With software, an interface is a module created to be "written to".
That is, if two programs are written to the same interface, then they can be successfully linked together.
IRQ Level (Interrupt Request Level): The notification a processor receives when another portion of the computer's hardware requires
its attention. IRQs are numbered so that the device issuing the IRQ can be identified, and so IRQs can be prioritized.
J
K
Kilobit: One thousand bits. A unit of measure for digital data rates.
Kilobyte: One thousand bytes. A unit of measure for digital data rates. Not to be confused with "K", which stands for z
10
bytes of
storage space, either in memory or on disk. 1K of disk space is actually 1024 bytes, 16K is 65,536 bytes and 1M (meg) is 1,048,576
bytes.
L
Leased Line: A private, dedicated communications channel that connects two locations. This connection lasts for the duration of the
subscription. Leased lines may be conditioned to improve line quality over that of dial-up lines.
Line Conditioning: An additional cost option offered by the telephone company for their leased, voice-grade lines. The service
provides a careful balance of line enhancements to improve the frequency response and to reduce distortion.
LRC (Longitudinal Redundancy Check): Error checking method that generates a parity bit from a specified string of bits on a
longitudinal track. In a row and column format such as on magnetic tape, LRC is often used with VRC, which creates a parity bit for
each character.
M
Mainframe: A large, powerful computer used to centralize a data processing environment. It has hundreds of gigabytes of disk storage
space. It uses a front end processor to connect directly to the communications channels that interconnect terminals and computers.
Megabyte: One million bytes when describing a data rate. 1M of disk space may actually mean 1,048,576 bytes.
Mid-range computer: A term coined by IBM referring to any of their Advanced Business Systems computers. This product line was
originally called their mini-computers, but as the number of supported users approached mainframe capabilities, the term "mid-range"
caught on.
Mnemonics: A term assigned to a complex idea, value, or list of information which is found to be representative of that information.
Computer commands are almost entirely mnemonics. Mnemonics are used as memory aids for people.