E

E.164
ITU-T recommendation for international telecommunication numbering, especially in ISDN, BISDN, and SMDS. An evolution of current standard telephone numbers.
E3
Wide-area digital transmission scheme used predominantly in Europe. It carries data at a rate of 34.368 Mbps. E3 lines can be leased for private use from common carriers.Compare with T3.
EBCDIC
An 8-bit character coding scheme developed by IBM. It is not compatible with ASCII character coding.
ECC
See Error-Correcting Circuitry (ECC).
editor
A program that allows the user to create and edit text.
EEPROM
See electrically erasable read-only memory (EEPROM).
EFS
See Enhanced Filesystem (EFS).
EFT
See Expanded Fundamental Types (EFT).
EIA
See Electronic Industries Association (EIA).
EISA bus
See Extended Industry Standard Architecture (EISA) bus.
ELAN-P board
The PCI-bus circuit board that provides full Ethernet support (all relevant IEEE 802.3u 10BaseT standards). This interface connects a IBM NUMA system using a PCI bus to a local area network (LAN).
electrically erasable programmable read-only memory (EEPROM)
A type of memory chip which can retain its contents without constant electrical power. Unlike the PROM which can be programmed only once, the EEPROM can be erased electrically. The processor section of the Symmetry SSM makes use of EEPROMs. See also erasable programmable read-only memory (EPROM), flash PROM.
electromagnetic interference (EMI)
Waves of electromagnetic radiation, including but not limited to radio frequencies, generated by the flow of electric current. Computer systems may radiate EMI, especially from high-speed data buses and communications ports; some components may also be vulnerable to EMI and must be shielded from it. All Symmetry systems incorporate special shielding to control their EMI emissions, as well as to protect them from EMI generated by other devices.
electronic data processing (EDP)
See automatic data processing (ADP).
Electronic Industries Association (EIA)
A professional organization that recommends standards, such as RS-232-C and RS-422, for the electronics industry. The EIA also provides guidelines for communications interface wiring, signal levels, and connectors.
electronic mail or E-mail
The transmission of messages over a communications network.
electrostatic discharge (ESD)
The flow of current that results when objects having a static charge come into close enough proximity to discharge.
electromagnetic interference (EMI)
Waves of electromagnetic radiation, including but not limited to radio frequencies, generated by the flow of electric current. Computer systems may radiate EMI, especially from high-speed data buses and communications ports; some components may also be vulnerable to EMI and must be shielded from it. All Symmetry systems incorporate special shielding to control their EMI emissions, as well as to protect them from EMI generated by other devices.
ELF
See Executable and Linking Format.
EMI
See electromagnetic interference (EMI).
emulation
  1. The use of programming techniques or special machine features to permit one computing system to execute programs written for another system.
  2. Performing (in hardware or software) functions normally performed by (other) hardware.
enable
  1. To make a system component or feature available for use by the operating system and other programs.
  2. To schedule a queue.
end-of-file (EOF) character
A character or other label that comes after the last record of that file and signals the end of the file.
End-System - Intermediate-System Routing (ISO 9542) (ES-IS)
Under Construction.
end user
The ultimate source or destination of information flowing through a system.
Enhanced Filesystem (EFS)
A filesystem format that allows group IDs (GIDs), user IDs (UIDs), and modes to be 32 bits in size. See also group ID, user ID.
ENQ
See enquiry character (ENQ).
enquiry character (ENQ)
A transmission control character used to request a response from the connected station; the response may include station identification, the type of equipment in service, and the status of the remote station.
Enterprise Cabinet
Tall IBM NUMA cabinet.
entity
See stream entity.
environment
In operating systems: Certain conditions in effect when the user is working with the operating system. At log-in, the shell sets up an environment. This environment defines variables such as type of terminal, search path used to locate commands, command prompt , and the name of the home directory. The user can use the default environment or modify it to meet individual needs.
environment variable
A variable that defines some aspect of the user environment. Examples include PATH, which defines the search path used to locate commands, and HOME, which contains the name of the home directory.
EOF character (end-of-file character)
A character or other label that comes after the last record of that file and signals the end of the file.
E_port
On an FC Switch, a special-function fabric port. E_ports are used to interconnect switches in a cascade to create a large fabric.
EPROM
See erasable programmable read-only memory (EPROM).
erasable programmable read-only memory (EPROM)
A type of memory chip that can retain its contents without electricity. Unlike the PROM which can be programmed only once, the EPROM can be erased by ultraviolet light, then reprogrammed. Examples include the EPROM used to store the firmware on the SCED board. See also electrically erasable read-only memory (EEPROM), flash PROM.
erase key
The key that deletes the last character you typed, moving the cursor to its previous position. By default, the erase key is <#>; it is commonly changed to <BackSpace>.
Error-Correcting Circuitry (ECC)
In IBM NUMA hardware: Special circuitry designed into Symmetry memory controller boards. The ECC can detect and correct single-bit errors in any byte of memory and detect (but not correct) double-bit errors.
ESD
See electrostatic discharge (ESD).
ES-IS
See End-System - Intermediate-System Routing (ISO 9542) (ES-IS).
Ethernet
A popular local-area network (LAN) developed by Xerox, Digital Equipment, and Intel. See also local-area network (LAN).
ETHER-I (Ethernet - ISA bus)
The IBM NUMA ISA-bus circuit board that provides full Ethernet support (versions 1 and 2 of IEEE specification 802.3). This interface connects the Symmetry 2000/40, which uses the EISA bus, to a local-area network (LAN). See also local-area network (LAN).
ETHER-V (Ethernet-VMEbus)
The IBM NUMA VMEbus circuit board that provides full Ethernet support (versions 1 and 2 of IEEE specification 802.3). This interface connects any IBM NUMA system that uses a VMEbus to a local-area network (LAN). See also local-area network (LAN).
event
In DYNIX/ptx: A security-related command or system call that can be audited.
exception
An abnormal condition (such as an I/O error) encountered in processing a data set or a file.
Executable and Linking Format (ELF)
OIn UNIX-based operating systems: The standard file format used for executable and object files.
execute
To run a program or command.
execute permission
For a directory, the ability to move to that directory by using the cd command. For a file, the ability to run a program contained in that file.
Expanded Fundamental Types (EFT)
A filesystem format that allows UIDs, GIDs, and modes to be 32 bits in size.
export
To make the value of a variable available to other programs.
Extended Industry Standard Architecture (EISA) bus
A bus standard for IBM compatibles that extends the Industry Standard Architecture (ISA) bus architecture to 32 bits and allows more than one central processing unit (CPU) to share the bus.
extensible architecture
A characteristic of IBM NUMAsystems by which you can easily add processors, memory, and peripherals.
extent
In ptx/EFS: A group of contiguous filesystem data blocks that are treated as a unit. An extent is defined by a starting block and a length.
extent attribute
In ptx/EFS: The extent allocation policies associated with a file.
extern
C-language keyword designating a function defined outside the program module.
External Data Representation (XDR)
A standard for machine-independent data structures, developed by Sun Microsystems.

F

fabric
A Fibre Channel entity which interconnectsand facilitates logins of N_ports attached to it. The fabric is responsible for routing frames between source and destination N_ports using address information in the frame header. A fabric can be as simple as a point-to-point channel between two N-ports, or as complex as a frame-routing switch that provides multiple and redundant internal pathways within the fabric between F_ports. See also F_port, Gigabaud Link Module, and N_port.
FADU
See File Access Data Unit (FADU).
failover disk group
A disk group that resides on shared disks but can be accessed by only one cluster node at a time. If the node that has the failover disk group imported loses cluster quorum, then I/O to the disk group is suspended so that another node in the cluster can safely import and use the disk group.
FCB
See function control block (FCB).
FC Bridge
See bridge (In Fibre Channel technology).
FC-P
See Fibre Channel Host Adapter.
FCP
See Fibre Channel.
FC port
A generic FC reference to an N_port or an F_port. See also fabric, F_port, and N_port.
FCS
See frame check sequence (FCS).
FDB
See fuse disconnection barrier (FDB).
FDDI
See Fiber-Distributed Data Interface (FDDI).
FENET board
The IBM NUMA Fast Ethernet board, which complies with the 10BaseT Ethernet standard.
FEP
See front-end processor (FEP).
fiber
In Fibre Channel: The signal-carrying medium, typically optical or metallic.
Fiber-Distributed Data Interface (FDDI)
A standard for high-speed fiber-optic local-area networks based on the token-ring standard.
fiber optic
Describing a transmission medium composed of a glass fiber light path surrounded by a cladding material that confines the signal to the light path.
Fibre Channel
An evolving ANSI interconnection standard for high-speed data transfer among computers and storage devices defined by the Fibre Channel Protocol (FCP). At the physical level, data is transmitted serially over pairs of point-to-point links between FC ports. With appropriate components, data can be transferred at 100 MB/sec up over a distance of 10 km between FC ports. The ports can be configured in ring and switched interconnect topologies which allow each port to exchange data with any other port that is part of the same fabric. See also fabric, FC port.
Fibre Channel Bridge
See bridge, in Fibre Channel technology.
Fibre Channel Host Adapter (FC-P)
A PCI-bus board that adapts the internal PCI bus of a Quad to an external Fibre Channel interface. The FC-P board in a Quad uses a GLM to create an N_port. See also Gigabaud Link Module (GLM), N_port.
Fibre Channel Protocol (FCP)
See Fibre Channel.
FID
See Format-Identifer Field (FID).
FIDU
See FTAM interface data unit (FIDU).
field
  1. A specific part of a record. Commands such as sort and cut can deal with individual fields on a line.
  2. An area, next to a menu system prompt, in which you can enter a response to the prompt.
field separator
A character, such as a tab or space, that separates the fields in a record.
FIFO (first-in, first-out)
Describing a data structure, such as a queue or buffer, from which the "oldest" (first-in) data is the first to be removed.
file
A collection of information in the form of a stream of characters. Files can contain data, programs, or other textual and numerical data.
File Access Data Unit (FADU)
  1. Elements or records of a file that can be manipulated individually.
  2. In DYNIX/ptx: One line of text in a file.
file access rights
The level of availability (read, write, execute) of a given file permitted a given user. Also called "file permissions."
filename
The human-readable identifier for a file stored on disk. See also pathname.
filename expansion
A shell feature that allows you to use metacharacters on the command line to match filenames. Also called "filename substitution."
filename extension
The characters in a filename that follow the last period in the filename; typically, these characters identify the file by type. For example, a file ending in .c is a C program file.
file server
A process running on one system that provides access to files on the system to programs on remote systems. The term "file server" is sometimes used to refer to the machine on which the files and the process reside.
fileset
In UNIX-based operating systems: A collection of files within a filesystem.
filesystem
In UNIX-based operating systems: A hierarchical collection of files and directories. The root filesystem is the source of the operating system.
filesystem block
In ptx/EFS: The minimum size of memory allocation in a filesystem. This is roughly equivalent to the UNIX filesystem (UFS) fragment size.
filesystem label
A label that identifies a filesystem. It has two parts: fsname, which corresponds to the directory mountpoint, and volume, which is a secondary identifier.
filesystem table
The /etc/fstab file. This file contains descriptions of all filesystems and specifies whether the filesystems should be mounted when the system is booted.
File Transfer Protocol (FTP)
In TCP/IP networking: A protocol used for tranferring files between two systems.
firmware
A program stored in EPROM that controls a peripheral or the system itself. See also erasable programmable read-only memory (EPROM).
firmware mode
For Symmetry systems, a run level in which all filesystems are unmounted, the operating system is not running, and only the firmware monitor is active. This run level is used to run stand-alone programs such as diagnostics. It is also the only run level at which power can safely be removed from the system.
Firmware Monitor
A part of the Symmetry system that runs tests, initializes devices, and carries out other procedures necessary to bring up the operating system. See Power-Up Monitor.
fixed extent size
In ptx/EFS: An extent attribute used to override the default memory-allocation policy of the filesystem.
fixed-length record
A characteristic of a file by which all records must have the same predefined length.
flash PROM
Similar to EEPROM, but capable of being reprogrammed without being removed from its location. Flash PROMs are used to store the firmware on the Symmetry SSM-2 board to allow it to be upgraded easily. See also electrically erasable read-only memory (EEPROM), erasable programmable read-only memory (EPROM).
flat-blade screwdriver
As opposed to Phillips-head (+), a screwdriver for slotted (-) screws.
floating-point
Describing a number in which the decimal point can occur in any position. In contrast, fixed-point numbers are defined as having a specific number of decimal places (as in currency) or none at all (integers).
floating-point accelerator (FPA)
A specialized integrated circuit, also known as a coprocessor, that intercepts and performs floating-point operations for a CPU. FPAs are often used to make computer systems run faster because they allow the CPU to concentrate on the integer operations which it performs much more quickly.
floating-point unit (FPU)
The portion of a microprocessor dedicated to floating-point operations (calculations involving floating-point numbers).
flow control
  1. The procedure for controlling the data-transfer rate. The purpose of flow control is to optimize the rate of flow (over the network) of message units for minimum congestion. The optimal rate is one at which the message buffers at the receiver and intermediate routing nodes do not overflow, and the receiver does not wait for message units.
  2. Regulation of the flow of messages within a stream and from user space into a stream, accomplished by the STREAMS scheduler.
FMD Services Layer
In SNA networking: The layer within a half-session that routes FMD requests and responses to particular NAU services manager components and that provides session network services or session presentation services, depending on the type of session.
FMH
See Function Management Header (FMH).
folder
In mailx, a file in which mail messages are saved.
font
A set of text or graphics characters having a particular size and style.
foreground
A mode of command execution that causes the shell to wait until a command executes before prompting you for another command.
fork
The action of a process creating another process.
form
  1. The paper on which output data is printed by a line printer or character printer.
  2. A menu-system display that lists prompts and provides fields for user input. The menu system runs commands or edits files based on that input.
format
To create an addressing scheme on a disk.
Format Identifier Field
In SNA networking: A field in each transmission header (TH) that indicates the format of the TH; that is, the presence or absence of certain fields. TH formats differ in accordance with the types of nodes between which they pass. See also transmission header (TH).
formatted
Describing a disk that is ready to be used by the system.
formatter
A program that is used to format disks.
FORTRAN (formula translation)
A computer language developed by IBM in 1956 and enhanced in 1966 and 1977. The first in which calculations to be performed could be specified in mathematical formulae, rather than as complex series of assembly language instructions. FORTRAN is used primarily in engineering and scientific applications. FORTRAN 77 (F77) is the implementation of FORTRAN which was adopted as a standard by the American National Standards Institute (ANSI) in 1977.
FPA
See floating-point accelerator (FPA).
F_port
In a fabric, an F_port, or "fabric" port, is an access point for connecting a user's N_port. An F_port facilitates N_port logins to the fabric from nodes connected to the fabric. An F_port is addressable by the N_port connected to it. In IBM NUMA systems, an F_port is implemented by a GBIC or GOT. See also fabric, FC port, Gigabit Interface Converter (GBIC), Gigabit Optical Receiver, and N_port.
FPU
See floating-point unit (FPU).
FQDM
See fully qualified domain name (FQDM).
fragment
  1. A portion of a file block.
  2. In TCP/IP networking: A part of an IP datagram that is divided for transmission over a network. A fragment has the same format as the datagram of which it is a part.
frame
  1. The time needed to transmit a block of data (including parity and other control information).
  2. A block of data and associated control information.
  3. See window frame.
frame check sequence (FCS)
Extra characters added to a frame for error checking.
frame control
The third byte of the multibyte token-ring packet. Defines two types of packets: IEEE 802.2 packets that carry user data or MAC packets that carry ring-management data.
Frame Relay
Industry-standard, switched data link layer protocol that handles multiple virtual circuits using HDLC encapsulation between connected devices.
free blocks
Blocks in a filesystem that are not being used by a file.
free shell strategy
A batch-processing strategy in which the login shell specified in the password file is executed. This shell then determines the shell to be used to execute the batch job.
front-end processor (FEP)
  1. An I/O processor that is used to format and process input data.
  2. In SNA networking: A processor that relieves the host processor of certain communications-related tasks, such as line control, message handling, and conversion functions necessary for transmission of data between the host and a communications network. Also called ''communication controller.''
FTP
See File-Transfer Protocol (FTP).
full backup
A backup that copies an entire filesystem or the complete contents of specific directories.
full-duplex
Describing a communications connection over which each device can transmit and receive simultaneously. See also duplex, half-duplex.
full pathname
See pathname.
fully qualified domain name (FQDM)
In networking: The full name of a system, consisting of its local hostname and its domain name. An FQDN is sufficient to determine a unique Internet address for any host on the Internet. The same naming scheme is also used for some hosts that are not on the Internet, but which share the same name space for electronic mail addressing.
function control block (FCB)
Under Construction.
function key
  1. On some terminals, a labelled key (such as <ATTENTION> and <ENTER>) that causes the transmission of a signal not associated with a printable or displayable character. Detection of the signal usually causes the system to perform some predefined function for the associated operator.
  2. A numbered key (such as <F12> and <PF3>) that generates a predefined sequence of characters, typically called an escape sequence. The ptx/ADMIN menu system uses function keys to perform such activities as running commands and exiting the system.
Function Management Header (FMH)
In SNA networking: One or more headers optionally present in the leading request units (RUs) of an RU chain that allow one half-session in a logical unit-to-logical unit (LU-to-LU) session to select a destination as the session partner and control the way in which the end-user data it sends is handled at the destination; change the destination or the characteristics of the data during the session; and transmit between session partners status or user information about the destination (for example, whether it is a program or device).
functional layers
In networking: Distinct layers into which network services are divided in order to increase the range,flexibility, and simplicity of interconnection among diverse systems. Common examples of such network protocols are Open Systems Interconnection (OSI) model and IBM's Systems Network Architecture (SNA).
fuse disconnection barrier (FDB)
Under Construction.

G

gateway
  1. Hardware that connects separate networks. A gateway contains network access and IP software. See also Internet Protocol (IP).
  2. In OSI networking: A transfer point between electronic mail networks. See also Open Systems Interconnection (OSI) model.
gateway-to-gateway protocol (GGP)
A MILNET protocol specifying how core gateways exchange reachability and routing information. See also Defense Data Network.
GB
See gigabyte (GB).
GBIC
See Gigabit Interface Card.
GCR
See group-coded recording (GCR).
GCR tape
Magnetic tape on which data is stored using the group-coded recording method. See also group-coded recording (GCR).
GDP
See government-domain part (GDP).
GDSP
See government-domain specific part (GDSP).
general format identifier (GFI)
Under Construction.
getty or get TTY
A process that waits at a TTY port for a user to log in. The getty process determines the appropriate line setting for the port, including the communication speed and login prompt, and then starts up the login process.
GFI
See general format identifier (GFI).
GGP
See gateway-to-gateway protocol (GGP).
GID
See group ID (GID).
Gigabaud Link Module (GLM)
An encoding/decoding device that is a Class-1 laser component assembly with transmitting and receiving receptacles that connect to fiber-optic cables. The GLM provides the link-control facility for an N_port. It converts electrical signals from parallel to serial to optical when transmitting, and the opposite when receiving. GLMs are not hot-swappable. See also N_port.
Gigabit Interface Converter (GBIC)
An encoding/decoding device that is a Class-1 laser component assembly with transmitting and receiving receptacles that connect to fiber-optic cables. GBICs perform a serial, optical-to-electrical and electrical-to-optical conversion of the signal. The GBICs in the switch are hot swappable. See also F_port.
Gigabit Optical Transceiver (GOT)
An integrated duplex data link for bidirectional communications over multimode optical fiber. Each transceiver consists of a transmitting and a receiving optical subassembly for SC-style cable connectors. GOTs perform only the optical-to-electrical and electrical-to-optical conversion of the signal. The GOT in the FC-AL Hub is a nonreplaceable Class-1 laser component assembly usually mounted on a host electronics board. Unlike the GLM device, the GOT does not perform the electrical conversion from serial to parallel, which takes place on the host board.
gigabyte (GB)
Roughly a billion (2**30) bytes.
GLM
See Gigabaud Link Module.
global
A term that defines the scope of a command as affecting an entire file.
global task table
In ptx/ADMIN: A menu-system file that contains information such as the names of users and groups who have access to specific menu-system tasks.
GOSIP
See Government Open Systems Interconnection Profile (GOSIP).
GOT
See Gigabit Optical Transceiver.
government-domain part (GDP)
Under Construction.
government-domain specific part (GDSP)
Under Construction.
Government Open Systems Interconnection (OSI) Profile (GOSIP)
A government procurement specification for OSI protocols. Through GOSIP, the government has mandated that all federal agencies standardize on OSI and implement OSI-based systems as they become commercially available. See also Open Systems Interconnection (OSI) model.
graphics display system
In ptx/XWM: The combination of graphics display, hardware, and X display server software that provides display services for client applications.
group
In the DYNIX/ptx operating system: A collection of logically related users for which the system administrator can set file access permissions. Groups are defined in the /etc/group file, which includes for each group a name, ID, and list of associated users.
group-coded recording (GCR)
A method of storing data on magnetic tape.
group ID (GID)
In the UNIX operating system: A string that uniquely identifies each group of users to the operating system. See also group.

H

half-duplex
Describing a communications connection over which only one device at a time can transmit data. See also duplex.
half-session
In SNA networking: A component that provides FMD services, data flow control, and transmission control for one of the sessions of a network addressable unit (NAU). See also network addressable unit (NAU).
hang
Of a program or computer: to stop executing, typically without means of recovery.
HASP (Houston Automated Spooling Program)
A remote job entry service developed by NASA to connect IBM 360 computers.
HDLC
See High-Level Data Link Control (HDLC).
Hdump
High-density dump to an 8-mm drive.
head
The part of a disk drive that moves across the disk and reads or writes data.
heartbeat
In ptx/AGENT: A periodic check of agent processes on a remote system, performed by the manager software.
hierarchical addressing
A type of DLPI Addressing that allows Sub-Network Access Protocol (SNAP) headers to be added to the 802.2 header (over Ethernet CSMACD) to support protocols like TCP/IP.
High-Bandwidth Interconnect (HBI)
In ptx/CLUSTERS: The SCSI bus and associated QCIC boards that connect the cluster nodes to the shared storage devices, specifically disks in Pbays, for large, fast data transfers.
High-Level Data Link Control (HDLC)
A bit-oriented data link control procedure incorporating error-detection protocols.
High-Performance SCSI and Ethernet (HPSE)
A functionally distinct portion of the CSM board which provides Symmetry 5000 and WinServer 5000 systems with high-performance SCSI and Ethernet services. See also System Services Section.
high watermark
See watermark.
Highly Scalable Bus (HSB)
A 64-bit bus which links the Symmetry 5000 or WinServer 5000 system's CPUs, memory, and I/O subsystems. A refinement of the Symmetry System Bus, the Highly Scalable Bus provides roughly twice the bandwidth of the SSB. Peripheral interface boards connected to the SSB allow the CPUs to access mass-storage devices, printers, and other peripherals that are connected to the SCSI bus and the VMEbus. Processor boards, Memory Controller boards, Memory Expansion boards, bus adapter boards, and peripheral controller boards are installed in the system backplane and connect to the system bus. The specific boards and the number of each that can be installed depend on the system.
Highly Scalable Bus Controller (HSBC)
A system board in S5000 and S5000 systems whose primary functions include generating clock impulses for data timing on the Highly Scalable Bus, and controlling arbitration and priorities for all boards on the system bus. The HSBC board also monitors memory and I/O accesses for time-out conditions, generates the reference voltage for the termination block on the system backplane.
history
In the Korn and C shells, a list of the commands the user has entered. Commands can be reexecuted from the history list.
home directory
The default working directory when the user logs in. Because it usually takes the same name as the login name, it is also called the user's login directory.
hop count
A measure of the links between two systems on a network. A hop count of 5 means that four gateways separate the source and destination machines.
host
  1. In ptx/XWM: A computer used to run client applications. A host computer may not have its own display and display server program; if not, the host computer's client applications connect to a display server over the network.
  2. In a network: A computer that primarily provides such services and tools as computation, data-base access, special programs, and programming languages.
  3. The primary or controlling computer in a multiple-computer installation.
host node
  1. A node at which a host processor is situated.
  2. In SNA networking: A subarea node that contains a system services control point (SSCP); for example, a System/370 computer with OS/VS2 and ACF/TCAM.
hot sparing
Availability of data is maintained by automatically copying data from a failing disk to a permanently available spare, which is called the "hot spare." (In ptx/SVM, a method of automatically restoring redundancy within a disk group.)
hot spot
An area of high I/O activity within a volume on a disk.
hot standby
The process of using a secondary local-area network (LAN) board as a backup device for the primary LAN board. If the primary board fails, the secondary board assumes the identity of the primary board so that LAN activity is uninterrupted. See also local-area network (LAN).
HPSE
See High Performance SCSI and Ethernet (HPSE).
HSB
See Highly Scalable Bus (HSB).
HSBC
See Highly Scalable Bus Controller (HSBC).
hung
Of a program or computer: having stopped executing, typically without means of recovery.
hunt sequence
A series of line settings that enable the system to try different communication speeds when a user logs in. The user presses <Break> to cycle through the line-speed settings.

I

ICCCM
See Inter-Client Communications Conventions Manual (ICCCM).
ICMP
See Internet Control Message Protocol (ICMP).
IDI
See initial domain identifier (IDI).
IEEE (Institute of Electrical and Electronics Engineers)
A professional society, one function of which is to define standard specifications for hardware and software. Examples include IEEE 796 (MULTIBUS) and IEEE 802.3 (Ethernet).
IEN
See Internet Engineering Notes (IEN).
immbroker
In ptx/CLUSTERS: The integrity manager mode broker command, a command-line interface for managing and monitoring a cluster.
IMS
See Information-Management System (IMS).
in-band access
Access that uses or shares a connectivity path with the customer data. It is equivalent to a customer connection to the system. One example includes the Tier 1/Tier2 system TCP/IP connection.
increment
To increase (a variable) in value, typically by a small amount (usually one).
incremental backup
A backup that copies only files that have been created or changed since the last full backup.
indication primitive
In OSI networking: The primitive passed from the Data Link Service (DLS) provider to the DLS user to indicate an internal event that is significant to the user. This event may be logically related to a remote service request or may be caused by an event internal to the provider. See also Data Link Service (DLS) provider.
indirect address extent
In ptx/EFS: An extent that contains references to other extents, as opposed to file data itself. A single indirect address extent references indirect data extents. A double indirect address extent references single indirect address extents.
indirect blocks
Data blocks that are not referred to directly by an inode. These data blocks contain portions of a large file.
indirect data extent
In ptx/EFS: An extent that contains file data and is referenced through an indirect address extent. See also indirect address extent.
industry standard architecture (ISA)
Unofficial name for the bus architecture of the IBM PC XT personal computer. This bus design included expansion slots for plugging in various adapter boards. Early versions had an 8-bit data path, later expanded to 16 bits. The "extended industry standard architecture" (EISA) further expanded the data path to 32 bits.
Information-Management System (IMS)
An early database management system provided by IBM.
inheritance
The practice of having a child process assume specific process attributes that are identical to, and copied from, its parent process. This also refers to inheritance of group ID (GID), user ID (UID), and permissions, depending on context.
init process
A process invoked during the boot procedure; it reads the /etc/inittab file and determines the proceses to start at each run level.
initial domain identifier (IDI)
Under Construction.
initiator
A SCSI-bus device capable of initiating and controlling a communication transfer over the bus.
inode

The part of a filesystem that stores information about a particular file or directory. The information includes the owner, group, permissions, file size, links, time the file was last used or modified, and location of disk blocks storing data in the file.

On filesystems with access control lists (ACLs), the inodes also store ACL information.

inode allocation unit
In ptx/EFS: A group of consecutive blocks that contain inode allocation information for a given fileset. This information is in the form of a resource summary and a free inode map.
input
The data on which a command or program acts. The data can come from the terminal, a file, or the output of another command.
input device
The mechanical devices with which you provide input to your system: typically, the keyboard and mouse.
input field
See field.
input mode
An operating mode used by the ed and vi editors and mailx. The ed and vi input modes allow you to add text to a file. The mailx input mode allows you to create and send messages.
input/output (I/O)
Generically, information transferred between the computer and an external device. Specifically, input is data received by hardware or software, and output is data generated by hardware or software.
Instruction Prefetch Buffer
A section of the Intel Pentium central processing unit (CPU) that retrieves new instructions in bursts from the code cache and stores them until they are decoded and executed.
Integrated Services Digital Network (ISDN)
Communication protocols proposed by telephone companies to permit telephone networks to carry data, voice, and other source material.
Integrity Manager (IM)
A distributed program in the ptx/CLUSTERS software that defines cluster membership and ensures that member nodes agree on the names and states of shared resources.
intent logging
In ptx/EFS: A logging scheme that records pending changes to the filesystem structure. These changes are recorded in a circular intent log.
interactive
Describing an application in which user input is required during operation, and each instance of user input elicits a response from the application.
Inter-Client Communications Conventions Manual (ICCCM)
Under Construction.
interface
A shared boundary. Examples include cables between devices, software applications that control communication between programs or computers, and registers (or other storage locations) accessible to two or more computer programs.
Interim Local Management Interface (ILMI)
Specification developed by the Asynchronous Transfer Mode (ATM) Forum for incorporating Network-management capabilities into the ATM UNI.
interface program
See printer interface program.
International Organization for Standardization (ISO)
A multinational organization charged with creating standards for a variety of technologies. A notable example of such a standard is the Open Systems Interconnection (OSI) model, a standard for network architecture. ISO members are designated standards organizations of participating nations.
International Telecommunications Union (ITU)
ITU works closely with all standards organizations to form an international uniform standards system for communication. Study Group XVII is responsible for recommending standards for data communications over telephone networks and publishes the V.XX standards and X.n protocols. See also International Telecommunications Union (ITU)-T.
International Telecommunications Union Standardization Sector (ITU)-T
Formerly called the CCITT, this international agency is responsible for making technical recommendations about telephone and data (including fax) communications systems for Post, Telephone and Telegraph (PTT) administrations and suppliers. See also International Telecommunications Union (ITU), Post, Telephone and Telegraph (PTT).
International Telegraph and Telephone Consultative Committee
See CCITT (Comite' Consultatif International des Te'le'graphie et Te'le'phonie) International Telegraph and Telephone Consultative Committee.
Internet
A single worldwide TCP/IP network composed of many networks (such as CSNET, NSFNET, and MILNET). It has also been called DARPA Internet, NSF/DARPA Internet, and Federal Research Internet, because it evolved from the implementation of the ARPA network, developed under the auspices of the U.S. Department of Defense and other federal agencies.
Internet Control-Message Protocol (ICMP)
A part of the Internet Protocol that handles control and error messages. Systems use ICMP to return reports of problems with datagrams to the datagrams' original source. See also Internet Protocol (IP).
Internet Engineering Notes (IEN)
Under Construction.
Internet Protocol (IP)
Adds network and host addresses to data transmitted with the TCP or UDP software, creating a self-contained data packet or datagram. IP is responsible for routing that data to the destination node.
interoperability
The ability of software and hardware on multiple machines from multiple vendors to communicate meaningfully.
interprocess communication (IPC)
The transfer of data among distinct programs, with implied guarantee of response.
interprocess communication elements
Shared memory, semaphores, and message queues.
interrupt
  1. One program taking precedence over another (of lower priority) in access to a commonly requested resource.
  2. A signal by which various system components communicate.
interrupt request (IRQ)
A signal on a dedicated hardware line of the ISA (Industry Standard Architecture) bus or the EISA (Extended ISA) bus that interrupts the CPU. See also industry standard architecture (ISA), extended industry standard architecture (EISA) bus, central processing unit (CPU).
I/O
See input/output (I/O).
I/O clustering
The grouping of multiple I/O operations for better performance.
ioctl system call

Performs low-level input- and output-control operations and retrieves device status information (see the ioctl(2) man page). Typical operations include buffer manipulation and query of device mode or status.

ioctl is used to control a wide variety of devices, including terminals, printers, and disk drives, as well as system interfaces such as STREAMS on DYNIX/ptx.ioctl manipulates data structures that are specific to the hardware or software being controlled, so the exact usage varies. The general terminal interface is described under termio(7). The STREAMS interface (DYNIX/ptx only) is described under streamio(7).

IP
See Internet Protocol (IP).
IP address
In TXP/IP networking: A 32-bit address assigned to each host on a network. An abstraction of the physical hardware address, an IP address includes a network portion and a host portion.
IPC
See interprocess communication (IPC).
IQ-Link
IBM's trademarked name for its implementation of the high-speed memory switch technology that connects Quads and allows them to appear to the operating system as a single system rather than a collection of systems. See also Quad.
IQ-Ring Module
An AC-powered, self-cooled, rack-mount module that acts as a high-speed switching hub to interconnect multiple quads with IBM's IQ-Link technology. This provides easier system configurability and greater availability. The IQ-Ring Module can reroute data if a quad should fail or need to be removed for servicing. See also IQ-Link and Quad.
IRQ
See interrupt request (IRQ).
ISA
Seeindustry standard architecture (ISA).
ISDN
See Integrated Services Digital Network (ISDN).
ISO
See International Organization for Standardization (ISO).
isochronous
ITransmission of data that is dependent upon timing. Examples include voice and video, which must be played back with the same timing that they were sent with. Isochronous data must either carry embedded timing information or depend on the carrier technology, such as the constant bit rate of Asynchronous Transfer Mode, to maintain uniform timing between individual elements of the data stream.
ITU
See International Telecommunications Union (ITU).

J

Japanese Language Support (JLS)
In DYNIX/ptx: A supplement to Native Language Support, which is a package of internationalization features from AT&T that were incorporated into the operating system. JLS provides processing of multibyte characters and other features that prepare software to operate in a Japanese locale.
job
A set of commands or a shell script and its associated execution environment.
job control
In UNIX-based operating systems, Korn and C shells: A feature that allows the user to stop or kill commands and restart stopped commands in the foreground or the background.
job ID
A name assigned by the batch system that uniquely identifies a batch job. A job ID has the form seqno.node_name, where seqno is the sequence number of the job and node_name is the system where the job originated.
job name
The first 15 characters of a job's script file. Otherwise, if the script is from stdin, the batch system uses "STDIN" as the job name.
jumper
A bridge used to close a circuit. A jumper allows you to select certain hardware characteristics, such as address and interrupt level.

K

KB
See kilobyte (KB).
kermit command
In UNIX-based operating systems: A command to transfer data between systems, using the Kermit communications protocol.
kernel
In UNIX-based operating systems: The part of the operating system that controls access to the computer, handles hardware resources, manages the computer's memory, maintains the filesystem, and allocates computer resources among users. The kernel provides system-service subroutines that can be accessed from system commands and other programs by system calls.
kernel configuration files
In the UNIX operating system: Text files used by the config program to create the files necessary to build a new kernel. These files define parameters used to size the kernel for performance and I/O capabilities. Kernel configuration files reside in /etc/conf/uts and describe a variety of parameters about the system on which the kernel will operate. These files also list all I/O controllers and peripheral devices that the kernel must be able to recognize.
kernel parameter
In UNIX-based operating systems: A value or set of values, specified in the kernel, that affects system performance. See also kernel.
keycap
In computer input devices: The character represented on the surface of a keyboard key.
keycode
In computer input devices: The unique numeric value generated when a key is pressed.
key switch
In IBM NUMA systems: The power switch on the S2000/290 computer system. It can be locked with a key to prevent the machine from being powered on by unauthorized persons.
keyword
  1. Any one of the words that compose a given programming language or set of operating-system routines. Also called ''reserved word.''
  2. A characteristic word, phrase, or code that is stored in a key field and used to sort or search records.
  3. A variable (such as DESTINATION CONTROL) that defines a particular portion of the BSC RJE (Remote Job Entry) environment. Every BSC RJE profile is made up of a series of keywords, each of which in turn has one or more parameters associated with it.
kill
In computer operating systems: To terminate a command.
kill key
In UNIX-based operating systems: The key that deletes the command line that is being typed. By default, the kill key is the "at" sign (@).
kilobyte (KB)
Roughly one thousand (2**10) bytes.
Korn shell
In UNIX-based operating systems: A shell program that provides features such as job control, command-line editing, and alias definition.

L

LAN
See local-area network (LAN).
LAN emulation (LANE)
In OSI networking: Technology that allows an ATM network to function as a LAN backbone. The ATM network provides multicast and broadcast support, address mapping (MAC-to-ATM), SVC management, and a usable packet format. See also Asynchronous Transmission Mode (ATM), switched virtual circuits (SVC), media access control (MAC).
LAP
See Link Access Procedure (LAP).
LAP-B
See Link Access Procedure - Balanced (LAP-B).
LAT
See Local Area Transport (LAT).
LAT Control Program (LCP)
A program used by the system's manager to administer the LAT host software. See also Local Area Transport (LAT).
latency
The amount of time it takes for a given piece of work to be completed. For filesystems, this typically refers to the amount of time it takes a given filesystem operation to return to the user.
LCGN
See logical channel group number (LCGN).
LCI
See local channel identifier (LCI).
LCP
See LAT Control Program (LCP).
leased line
See dedicated line.
LED
See light-emitting diode (LED).
LEN
See low-entry networking (LEN).
license
In ptx/LICENSE: An instance of permission to use a licensed software product or service. Sometimes, a user needs more than one license to use a product.
license annotation
In ptx/LICENSE: A string that modifies the use of a license in a manner defined by the vendor of the software product. license database.
license database
In ptx/LICENSE: The database of licenses maintained by a license server. The license database file lic_db resides in the /usr/lib/netls/conf directory.
license information
In ptx/LICENSE: The information that describes licenses. This information consists of the product name, the product version, the number of licenses, the license type, the start and end dates of the licenses, the target type, the target ID, and a time stamp.
license management daemon
In ptx/LICENSE: A software program that administers licenses for software products, invoked with the command netlsd. The netlsd command can be found in the /usr/lib/netls/bin directory.
license password
In ptx/LICENSE: A string encoded with license information for a software product.
light-emitting diode (LED)
An electronic component that lights up when current passes through it, producing relatively little heat for the amount of light output. Used as activity and status indicator on computer systems and components.
line address
In UNIX-based operating systems, editors ed and vi: The location of each line in the editing buffer.
line-discipline module
In network programming for UNIX-based systems: A STREAMS module that processes line data in the I/O stream to control the format and flow of data into and out of the system, for example, erase- and kill-character handling. See also STREAMS.
line number
In UNIX-based operating systems editors ed and vi: The number of each line in the buffer, which is used to display the line on the screen.
line setting
A set of line characteristics, such as the communication speed, for a TTY line. These characteristics allow the computer to communicate with a specific peripheral device.
link
  1. In UNIX-based filesystems: A filename that refers to another file. You can use the ln command to create multiple filenames (typically in different directories) for a single file.
  2. In network architecture: A connection between "adjacent" nodes in a network.
  3. In Fibre Channel technology: Two unidirectional fibers carrying data in opposite directions, along with their associated transmitters and receivers; also refers to the full-duplex physical association (FC-0 level) between transmitting entities (FC-1 level) in directly-attached ports.
Link Access Procedure (LAP)
The link-level elements used for data interchange between data-circuit terminating equipment (DCE) devices and one or more data-terminal equipment (DTE) devices. See also data-circuit terminating equipment (DCE), data-terminal equipment (DTE).
Link Access Procedure - Balanced (LAPB)
A procedure for gaining access to an X.25 network at the link level. LAPB uses a full-duplex, asynchronous, symmetric (balanced) protocol used in point-to-point communication.
link connection
The transmission medium that establishes the link between network nodes, for example, telephone lines, coaxial cable, and fiber optic cables.
Link_Control_Facility
A hardware facility that manages transmission and reception of data over a Fibre-Channel link. It is contained within each N_port of a node and F_port of a fabric. See also F_port, and N_port.
link station
The end point of a link connection. Link stations use the data link control - layer services to ensure that link data arrives without error.
linker
In programming: A program that resolves external references among compiled modules that are to be used together.
LLC
See Logical Link Control (LLC).
load balancing
A method of distributing batch jobs across a set of queues or across a set of node/queue pairs for the purpose of equalizing the workload.
loader
A program that copies an executable image into main memory, in preparation for execution of that image.
loading
  1. Transferring data or an executable program from storage into memory for processing or execution.
  2. Transferring files on the BSC RJE release media to the local computer.
local-area network (LAN)
A network that connects several devices in a limited area (such as a building or campus). LANs are privately owned and administered. In addition, they are self-contained, in that they do not depend on public telephone networks. See also wide-area network (WAN).
Local Area Transport (LAT)
Digital Equipment Corporation's Local Area Transport architecture, which is a non-DECnet set of protocols for transferring data over an Ethernet data link. See also Ethernet.
local channel identifier (LCI)
Under Construction.
local configuration file
In computer operating systems: A system configuration file that has been modified for a specific system. Typically, a local configuration file is created by copying the default system configuration file and making desired changes to the copy. A local system-configuration file must be given a new name.
Local Integrity Manager (LIM)
In ptx/CLUSTERS: The component of the Integrity Manager that is responsible for local node activity, primarily the management of the local view of shared disks. See also Integrity Manager (IM).
local management
The phase in either connection mode or connectionless mode in which a transport user establishes a transport endpoint and binds a transport address to the endpoint. Functions in this phase perform local operations and require no transport-layer traffic over the network.
locale
All necessary components, including software, messages, code sets, and mapping tables, that are required for programs to operate in a local natural language, using local conventions for information such as currencies, date, and time.
localization
Conversion of software to a specific local operating environment. This can include translating program messages, specifying date and time format, and other tasks.
Lock Manager
In ptx/CLUSTERS: A kernel-resident program that regulates and coordinates application access to a cluster's shared resources.
Lock Manager domain
In ptx/CLUSTERS: A unique name space assigned to an application to avoid potential resource-name conflicts.
log file
A file that records system activity. For example, /usr/lib/cron/log records each command run by the cron process.
logical channel group number (LCGN)
Under Construction.
log in
To start an interactive session with the computer. Before you can use the operating system, you must type your login name and password. The system uses this information to verify that you are an authorized user.
logical IP subnet (LIS)
In networking: A group of hosts that are configured as members of the same Internet Protocol (IP) subnet. That is, they have the same IP network and subnet numbers.
Logical Link Control (LLC)
  1. One of the two sublayers of the OSI data link layer; the other is Medium Access Control (MAC). LLC supports media-independent data-link functions; as a standard, it refers to the protocol defined in IEEE 802.2 for the LLC interface to the network layer. See also Medium Access Control (MAC).
  2. That part of a data station that supports the LLC functions of one or more logical links. The LLC generates command protocol data units (PDUs) and response PDUs for transmission and interprets received command PDUs and response PDUs. Specific responsibilities assigned to an LLC include: initiation of control signal interchange; organization of data flow; interpretation of received command PDUs and generation of appropriate response; error control and recovery functions in the LLC sublayer.
logical record
A group of logically related fields. Portions of the same logical record may be located in different physical records, and several logical records or parts of several logical records may be located in one physical record.
logical unit (LU)
In SNA networking:A port or window that provides end-user access to SNA for communication with another user and use of the functions provided by system services control points (SSCPs). An LU can support at least two sessions--one with an SSCP and one with another LU--and may be capable of supporting many sessions with other LUs. LUs are software-implemented logical ports with unique names and addresses.
logical unit (LUN)
In mass-storage management: A virtual device created by logically dividing up and recombining a group of physical storage media, such as magnetic disks. In RAID (redundant array of inexpensive disks) architectures, for example, a logical unit may be configured by distributing and/or duplicating data over several physical disks. Depending on the particular RAID configuration, this arrangement may improve performance by allowing different segments of a data stream to be written to multiple disks simultaneously, or improve availability by writing identical data to two disks, so that if one fails, the data is preserved on the other.
Logical Unit Number (LUN)
In SNA networking: A numeral identifying one of the upper-level protocols for data transfer among various hardware devices and software environments. For example, LU 1 is the protocol for data transfer between an application program and an SNA-compliant printer or workstation. LU 6.2 is a device-independent program-to-program communications protocol.
log out
To end an interactive session with a computer and exit the operating system.
logging
The recording of data about specific events on the system, such as errors.
login account
Information about the user stored by the operating system. The information includes the user's login name, home directory, password, group, and default shell program. It can also include some miscellaneous information such as a phone number.
.login file or login file
A C-shell start-up file that executes when a user logs into the system. It contains commands and variables that affect the user environment.
login name
The human-readable version of the name by which the user is known to the computer. The user enters this name upon logging into the system.
login shell strategy
With this strategy, the user's login shell is executed to interpret the job script.
logname
See login name.
logon
IBM terminology for the procedure by which a user begins a terminal session.
loop count
In programming: The number of times a program has executed a section of code.
loopback fixture
A specially wired connector or set of connectors, used for diagnostic testing, that allows a controller board to transmit signals at one pin or connector while receiving them at another. A loopback fixture may be designed to check one port at a time by transferring signals from one pin to another on the same connector (single-port loopback), or two ports at a time by exchanging signals between connectors (double-port loopback).
loopback testing
The process of sending data through network components and returning it for comparison (also called mirror testing).
low-entry networking (LEN)
Under Construction.
lower multiplexer
See multiplexer.
Low-Latency Interconnect (LLI)
A dedicated local-area network (LAN) that carries Integrity Manager (IM) and Lock Manager (LM) traffic between cluster nodes. See also Integrity Manager (IM), local-area network (LAN), Lock Manager (LM).
low watermark
See watermark.
lower stream
A stream connected below a multiplexer by means of an ioctl I_LINK system call. The downstream end of a lower stream terminates at a driver or another multiplexer.
LP scheduler
The lpsched program, which controls LP Print Service. When the scheduler is running, it picks up print requests and sends them to the appropriate printer interface program, which prepares the requests and sends them to the printer. The print service can operate only when the scheduler is running.
LPDEST environment variable
In UNIX-based operating systems: An environment variable that specifies a default destination printer.
lpsched command
See LP scheduler.
ls_admin
In ptx/LICENSE: The software program used to modify a license server database.
ls_rpt
In ptx/LICENSE: The software program that reports on the history of license server events.
ls_stat
In ptx/LICENSE: The software program that reports on the status of licenses.
ls_tv
In ptx/LICENSE: The network license management daemon test and verification tool.
LU
See logical unit (LU).
LU Services Manager
In SNA networking: A component that provides a logical unit (LU) with network services and end-user - to - end-user services. The LU services manager provides services for all half-sessions within the LU.
LU-to-LU session
In SNA networking: A session between two logical units (LUs) in an SNA network. It provides communication between two end users or between an end user and an LU services component.
LUN
See logical unit number (LUN).
Lynxer
In IBM NUMA systems: A program, lynxer.elf, that initializes firmware and loads the bootstrap program.