Glossary
address A unique number assigned to a device on a network. For example, a twinax terminal must be assigned a unique address before it is able to access the host system.
AIX (Advanced Interactive Executor) IBM’s version of the UNIX operating system, which is run on the IBM RS/6000s.
application server A computer in a client/server environment that performs the data processing. In a two-tier client/server environment, the user’s machine performs the data processing, which connects to the database server (DBMS). The bulk of client/server architecture is two-tier. In a three-tier client/server environment, an independent application server performs the data processing.
ASCII (American Standard Code for Information Interchange) A 7-bit binary data code used in text-only communication with most minicomputers and personal computers.
AS/400 (Application System/400) An IBM minicomputer series introduced in 1988 that runs under the OS/400 operating system. It is IBM’s midrange series of computer systems used primarily for business applications. The AS/400 was designed to replace the System/36 and System/38, IBM’s previous midrange computers. The AS/400 serves in a variety of networking configurations: as a host or intermediate node to other AS/400s and System/3x machines, as a remote system to mainframe-controlled networks and as a network server to PCs.
balun (BALanced/UNbalanced) An impedance-matching transformer device used to connect balanced twisted-pair cabling to unbalanced coaxial (or other) cabling. Common in IBM cabling systems.
BNC connector (Bayonet Neill Concelman) A cable connector used in 10Base2 ethernet and in mainframe (3270) coaxial networks. Also known as a coax connector.
bus and tag cables Channel cables (copper wire) that attach a peripheral device (such as a printer, tape subsystem, or communications controller) to a local mainframe host. Always used in pairs: one “bus” that carries the data, and one “tag” that carries the control information.
bus and tag channel A common name for the parallel channel between IBM mainframes and peripherals.
cathode-ray tube (CRT) The display screen used in most televisions and standard computer monitors. An electron beam moves across the back of the screen, lighting up phosphor dots inside the glass tube, which causes an image to be displayed outside the screen.
centronics parallel A standard 36-Pin interface for connecting parallel printers to PCs.
characters per second (CPS) Measure of speed of dot-matrix printers; the higher the number, the faster the printer.
coax A common term for coaxial cable. See coaxial cable.
coaxial cable Cable in which a solid piece of copper is surrounded by insulation and a tubular piece of copper braid, wrapped in a plastic cover. Although similar in appearance, there are several types of coaxial cable, one of which is used to attach 3270 peripherals to the mainframe network.
communications hardware Equipment that facilitates connections between computers and computer systems–for example, over phone lines using a modem.
continuous-forms paper Paper in which each sheet is connected together; used by most dot-matrix printers.
controller In the IBM mainframe and midrange environments, a controller allows peripherals like terminals and printers access to the host. The controller acts as a traffic director, but it can also function as a protocol converter, allowing dissimilar networks access to the host.
CPS See characters per second.
CRT See cathode-ray tube.
DB9, DB15, DB25 D-shaped connectors used in data communications. The number indicates the number of possible pins in the connector.
DHCP (Dynamic Host Configuration Protocol) A protocol designed to assign IP addresses dynamically upon system startup.
DIN connector (Deutsches Institut fur Normung connector) A family of plugs and sockets used to connect a variety of devices. Earlier PC keyboards use a five-pin DIN. The PS/2 connector uses a smaller 6-pin Mini-DIN.
dots per inch (DPI) A measure of a printer’s degree of sharpness, expressed in the number of ink (or toner) dots the printer can place in one square inch. The larger the DPI, the sharper the printed image.
dot-matrix printer A printer that arranges printed dots to form characters and images.
DPI (Dots Per Inch) See dots per inch.
DSU (Data Service Unit) A device that transmits data over digital circuit (DDS or T1); combined with a CSU (Channel Service Unit).
dumb terminal A type of workstation that has no computing power of its own. The mainframe or midrange host computer does all the processing. The terminal displays data and transmits the user’s keystrokes and mouseclicks. Limited to text and some rudimentary graphics applications.
EBCDIC (Extended Binary Coded Decimal Interchange Code) An 8-Bit character code used primarily in IBM 3270 and 5250 environments; compare to ASCII.
EIA (Electronic Industries Association) A standards organization in the U.S. specializing in the electrical and functional characteristics of interface equipment. It used to designate its recommended standards with the “RS-” prefix (“RS-232,” “RS-485,” etc.); now it designates them with the “EIA-” or “EIA/TIA-” prefix.
emulation The imitation of one device by another. The emulating device performs the same functions and appears to other network devices as if it were the emulated device.
ESCON (Enterprise Systems CONnection) An IBM mainframe fiber-optic channel that transfers 17 Mbytes/sec over distances up to 60 km depending on connection type. ESCON allows peripheral devices to be located across large campuses and metropolitan areas. Compared to the copper-based, parallel bus and tag channels, ESCON provides greater speeds and uses a serial interface.
ES/9000 The IBM Enterprise Systems Architecture/390 (ESA/390) water- and air-cooled mainframe line produced from 1990 to 1998 that uses 31-bit addressing with maximum memory capacities from 256 Mb to 9 GB, up to 128 channels, and up to four processors.
ethernet The most widely-used LAN access method (Token-Ring is the next most popular). Ethernet is normally a shared media LAN. All stations on the segment share the total bandwidth, which is either 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet) or 1000 Mbps (Gigabit Ethernet). With switched Ethernet, each sender and receiver pair have the full bandwidth.
fiber optic cable A type of network cable consisting of fiber optic strands that transmits data using light rather than electricity.
file server A high-speed computer in a network that stores the programs and data files shared by users. It acts like a remote disk drive. The difference between a file server and an application server is that the file server stores the programs and data, while the application server runs the programs and processes the data.
firmware Operating instructions stored for the long term in a device’s read-only memory.
front end processor A hardware device linked to one or more host computers; performs data-communications and network-processing functions for the attached computers. In IBM SNA networks, an IBM 3725 or 3745 communications controller.
function keys Computer keyboard keys that are labeled F1, F2, and so on; usually positioned along the top or left side of the keyboard.
gas plasma monitors Flat-panel monitors that use gas plasma technology, providing a layer of gas deposited between two sheets of material. When voltage is applied the gas glows and produces the pixels that form an image. The 3290, with a red-orange screen, is IBM’s only gas-plasma display.
high resolution A term that refers to monitors or printers that produce high-quality output because they generate more dots per inch (DPI).
host computer The central computer (or one of a collection of computers) in a data-communications system. It handles the system’s primary information-processing functions.
hub A device that provides a central point of cable connection.
ICA (Independent Computing Architecture) The core of Citrix’s MetaFrame and WinFrame software which enables a Windows or UNIX server to run an application for multiple users simultaneously while sending only the changes in the user interface to the client machine. This is similar to the days of mainframes, but with a graphical interface rather than character based. ICA client support includes Windows, DOS, Macintosh, UNIX, Java and Web browsers. Numerous embedded devices are ICA enabled as well.
IP Address (Internet Protocol address) The address of a computer attached to a TCP/IP network. Every client and server station must have a unique IP address. Client workstations have either a permanent address or one that is dynamically assigned to them each dial-up session. IP addresses are written as four sets of numbers separated by periods; for example, 204.171.64.2.
IPDS (Intelligent Printer Data Stream) IBM’s proprietary printer datastream for advanced print functions such as vector graphics, resident bar codes, OCR A and B, raster image, and electronic forms (overlays).
Kbps (Kilobits Per Second) A standard measurement of data rate and transmission capacity, equal to 1000 bits per second.
LAN See local area network.
local area network (LAN) A computer network limited to the immediate area, usually the same building or floor of the building.
laser printer Nonimpact printer similar to a photocopying machine; images are created on a drum, treated with a magnetically charged ink-like toner (powder), and then transferred from drum to paper.
LCD See liquid-crystal display.
legacy system An old information system still in use.
light pen Light-sensitive pen-like input device connected by a wire to a computer terminal; the user brings the pen to the display screen and presses the pen button, which identifies that screen location to the computer.
line printer High-speed impact printer that prints an entire line at a time.
liquid-crystal display (LCD) Technology used for flat-panel displays instead of cathode-ray tubes (CRT), which are used in standard monitors. LCD displays are commonly used in laptop computers and calculators. There are monochrome LCD displays, which appear gray, and there are color LCDs. The three basic types of LCD displays are passive-matrix, dual-scan, and active-matrix.
logic In the context of terminals, short for logic module.
logic module The part of a terminal that manages input and output of data. Most commonly an external module with a monitor keyboard attached to it, but it can also be integrated into the monitor.
mainframe A large computer that has access to billions of characters of data and is capable of processing large amounts of data very quickly. Capable of serving hundreds to several thousands of users.
MAU (Multistation Access Unit) A wiring concentrator used in Token-Ring LANs.
Mb (Megabyte) A unit of computer storage equaling about one million bytes.
Mbps (Megabits Per Second) A standard measurement of data rate and transmission capacity, equal to 1,000,000 bits per second.
MetaFrame Software from Citrix that supports “application server computing,” in which the application runs in the server for multiple users. The core technology in MetaFrame is the ICA (Independent Computing Architecture) protocol which governs the input/output between client and server. The timeshared, multiuser processing that takes place is provided by the native capabilities of UNIX or the Terminal Server options in Windows NT and 2000. Using Citrix’s MetaFrame software on top of Windows Terminal Server adds the ICA protocol, which is supported by a huge number of client types, including Windows, OS/2, DOS, Linux, UNIX, Macintosh, Java-based apps as well as Web browsers. In addition, ICA provides the flexible, resizable graphical windows that users are accustomed to.
midrange A computer larger than a microcomputer but smaller than a mainframe, such as the IBM AS/400. IBM RS/6000s are also called midrange computers. Midrange computers are designed to be hosts in multi-user environments.
mini-DIN A small type of DIN connector most often used for keyboard and mouse connection.
monochrome Monitors that display only one color. Usually characters on the screen are displayed in green, amber, or white on a dark background. However, some users prefer “reverse video,” which displays dark letters on a green, amber, or white background.
multiplexer A device that allows one channel to communicate with multiple sources simultaneously. Often shortened to “mux.”
near letter quality (NLQ) Print that is slightly less clear than letter quality.
NLQ see Near Letter Quality.
parallel channel 1. A channel that transmits data over several wires simultaneously, typically in increments of a byte (32-bit channel, 64-bit, etc.). 2. A parallel channel for IBM (and other) mainframes that transmits up to 4.5MB/second. IBM’s parallel channel is also known as a bus and tag channel.
parallel port A port normally used to connect printers to workstations.
parallel transmission Transmitting one or more bytes at a time using multiple communication lines.
peripheral In the mainframe and midrange environments, a piece of hardware connected to the host computer, such as workstations, printers, routers, controllers, front end processors, external disk, and external backup devices.
pixel The smallest indivisible part of a video image.
port A communications connection on a computer or a remote controller.
print server A network device that handles network printing.
protocol The procedures used to control the orderly exchange of information between stations in a network or system. An agreed way for two network devices to talk to each other.
protocol converter A device that translates from one communications protocol into another, such as IBM SNA/SDLC to ASCII.
RAM (Random Access Memory) The physical semiconductor based memory in a computer. One byte of RAM can hold one character, one Kb of RAM can hold 1024 characters, etc.
repeater In digital transmission, equipment that receives a signal, amplifies it, re-times it, and then reconstructs the signal for retransmission.
RJ-11 Wiring with 4 or 6 wire modular connectors; commonly used for standard telephone lines.
RJ-45 Wiring with 8 wire modular connectors; commonly used for serial data transmission.
RS-232 The industry’s most common serial interface standard; similar to and compatible with EIA-232, and the CCITT standards of V.24 and V.28.
RS-422 EIA serial transmission standard that extends transmission speeds and distances beyond those of RS-232. It is a balanced system with a higher level of noise immunity.
RS-423 EIA serial transmission standard that extends transmission speeds and distances beyond those of RS-232. It is a unbalanced system. Compare to RS-422.
RS/6000 (RISC System/6000) An IBM family of RISC-based servers that use AIX, IBM’s version of the UNIX operating system.
S/390 An abbreviation for IBM’s System/390 mainframe family of machines. Today, IBM’s 2003 CMOS-based System/390 systems are designated S/390s, and range from 1- to 5-way processors, 4 – 128 channels and 128 Mb to 4 GB memory.
serial transmission Transmitting data one bit at a time. Contrast with parallel transmission.
session A logical connection between two stations that allows them to communicate.
SNA (Systems Network Architecture) The total description of the logical structure, formats, protocols, and operating sequences for transmitting information between IBM software and hardware devices in the mainframe and midrange environments (S/390, AS/400 and their predecessors).
SVGA (Super VGA) A measure of a monitor’s clarity. Higher resolution than VGA: at least 800 x 600 pixels.
System/36 A multiuser, multitasking minicomputer from IBM that was introduced in 1983. It superseded the System/34 and is mostly compatible with it. System/34 programs run in the System/36 after recompilation. The typical system supports a few to a couple of dozen terminals. Although superseded by the AS/400, System/36 applications have to be recompiled to run on it. As a result, a large number of System/36s still remain in use. With the announcement of the AS/400 Advanced System/36, which runs System/36 applications natively, it is expected that System/36s will finally fade into history.
System/38 Family of IBM midrange multiuser SNA minicomputers introduced in 1978. Predecessors of the System/36, they are designed to host a few to several hundred users. They have been replaced by the AS/400.
TCP/IP (Transmission Control Protocol/Internet Protocol) The collection of transport and applications protocols used to communicate on the Internet and other networks, regulating how data is transferred between computers.
telnet A terminal emulation protocol commonly used on the Internet and TCP/IP-based networks. It allows a user at a terminal or computer to log onto a remote device and run a program.
terminal server A computer or controller used to connect multiple terminals to a network or host computer.
thin client A “thin processing” client in a client/server environment that performs very little data processing. The client processes only keyboard input and screen output, and all application processing is done in the server. Examples are X Window terminals and Windows terminals.
Token-Ring A LAN-access mechanism and topology developed by IBM in which a supervisory token is passed from station to station in sequential order. Stations wishing to gain access to the network must wait for the token to arrive before transmitting data.
tn3270 A special version of the telnet protocol that supports the IBM 3270 terminals.
tn5250 A special version of the telnet protocol that supports the IBM 5250 terminals.
twinaxial cable A cable that is similar to coaxial cable, but has two inner conductors instead of one. Used in IBM midrange systems such as Systems 34, 36, and 38, and AS/400. Often shortened to “twinax.”
twinax See twinaxial cable. Often used as a shorthand for the IBM midrange terminal and printer family.
UNIX A multiuser, multitasking operating system that is widely used as the master control program in workstations and especially servers. A myriad of commercial applications run on UNIX servers, and most Web sites run under UNIX. There are many versions of UNIX, and, except for the PC world, where Windows dominates, almost every hardware vendor offers it either as its primary or secondary operating system.
V.24 A CCITT interface recommendation defining interchange circuits; similar to and compatible with RS-232.
V.35 A CCITT interface standard for high-speed communication.
VGA (Video Graphics Array) A video standard for IBM PC and compatible computers. Standard VGA has a resolution of 640 x 480 and supports 16 colors.
web browser Client software that requests and displays HTML documents and other Internet or intranet resources.
Windows-based terminal A specialized input/output terminal for a Windows NT or Windows 2000 server running multiuser software such as Windows Terminal Server, WinFrame or MetaFrame. The terminals function like mini and mainframe terminals, where all the processing is done in a central host and only the input and output is performed at the terminal.
Windows Terminal Server Known officially as Windows NT 4.0, Terminal Server Edition, it is an option in NT that enables an application to be run simultaneously by multiple users at different Windows PCs. Windows Terminal Server turns an NT server into a centralized, timeshared computer, like the mainframe/dumb terminal environment. The difference is that Windows Terminal Server provides the familiar Windows graphical interface, whereas mainframes provide primarily character-based interfaces. All the data processing is performed in the server, and the client PCs display only the user interface and screen changes.
WinFrame Software from Citrix Systems that turns a Windows NT 3.51 server into a centralized, timeshared computer. Windows applications are run in the server and only screen changes are sent to the client machines.
workstation Any computer connected to a network.
10Base2 A 10 Mbps ethernet network implemented on thin RG58 coaxial cable, commonly known as “thin ethernet” or “thinnet”. The maximum length of a single cable is 600 feet.
10Base5 The original 10 Mbps ethernet network standard implemented on thick, yellow-jacketed cable. Also called “thick ethernet” or “thicknet”. The maximum length of a single cable is 1,640 feet.
10BaseT A 10 Mbps ethernet network implemented on twisted-pair cable. The maximum length of a single cable is 330 feet.
3270 A family of IBM terminals, printers and other peripheral devices that attach to mainframe systems. The earliest terminals were the IBM 3277 and 3278–hence the “3270” family designation.
5250 A family of IBM terminals, printers, and other peripheral devices that attach to IBM midrange systems (System/3x, AS/400). The earliest terminal was the IBM 5251, from which the “5250” family designation came.
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