M

MAC address
A standardized data-link layer address required for every port or device that connects to a local-area network (LAN). Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures. MAC addresses are 6 bytes long and are controlled by the IEEE. See also local-area network (LAN).
mailbox
A file containing the mail messages sent to a particular user.
Mail Transfer Agent (MTA)
In electronic mail: The program that delivers E-mail messages. Upon receiving a message from another MTA or a Mail User Agent, the MTA analyzes the recipients and then, in the case of a local addressee, delivers the message; in the case of an addressee at another location, the MTA routes the message to another MTA. For UNIX-based operating systems, sendmail is the most widely used MTA. See alsoMail User Agent (MUA), sendmail.
Mail User Agent (MUA)
In electronic mail: The program that allows users to compose and read E-mail. The MUA provides the interface to the Mail Transfer Agent: outgoing mail is sent to the MTA for routing; incoming mail is picked up from the MTA for delivery. See also Mail Transfer Agent (MTA).
mailx command
In electronic mail: Invokes the System V implementation of the Berkeley Mail mailer. See also .mailrc file.
Main board
In the FC Bridge, the primary electronics assembly that provides the Fibre Channel interface (an N_port), performs the translation between the Fibre Channel protocol and the SCSI bus protocol, and provides the interface and connectors for SCSI ports 0, 1, 2, and 3. The FC Bridge uses a GLM to creat an N_port. See also bridge (In Fibre Channel technology), N_port.
mainframe
A large, powerful computer system for computationally intensive tasks. Typically supports many users and requires a controlled physical environment.
major number
In UNIX-based operating systems: An identification number that specifies a device type, such as terminal or disk to the operating system. See also minor number.
make command
In UNIX-based operating systems: An operating-system command for compiling and linking software modules into an executable program.
Makefile
A descriptive file used by the make command in which the user specifies:
man command
In UNIX-based operating systems: Displays the specified man page. See also man pages.
man pages
In UNIX-based operating systems: Online documentation for operating-system commands, subroutines, system calls, file formats, special files, stand-alone utilities, and miscellaneous facilities. Invoked by the man command. See also man command.
Management and Diagnostics Controller (MDC)
A card in each Quad and in the IQ-Ring Module that provides a private Ethernet connection between those subsystems and the console PC. Each Quad contains one of these boards, which control diagnostics and communicates with the console PC. See also IQ-Ring Module, Quad.
Management Information Base (MIB)
In ptx/AGENT: A directory containing a set of standardized attributes for each networked computer or peripheral being managed under the Simple Network Management Protocol (SNMP). See also Simple Network Management Protocol (SNMP).
manager
In ptx/AGENT: The local system running the manager process. Agent processes report their status to the manager process.
Manchester encoding
In data communications: A baseband transmission scheme that specifies an "on" bit (1) by a high-to-low voltage change and an ''off'' bit (0) by a low-to-high change.
Manufacturing Automation Protocol (MAP)
A set of standards for automated mechanical design and manufacturing, developed by a group of U.S. manufacturers.
MAP
See Manufacturing Automation Protocol (MAP).
master system
In UUCP: The system that initiates a conversation.
MAU
See multiple access unit (MAU).
maximum transfer unit (MTU)
Under Construction.
MB
See megabyte (MB).
MBAD Board (MULTIBUS Adapter Board)
In Symmetry 2000 systems: Together with an MBIF board, provides a link between the MULTIBUS card cage and an optional MULTIBUS expansion unit. An MBAD board is installed in the system card cage and connects the system bus with the MULTIBUS system.
MBIF board (MULTIBUS Interface Board)
In Symmetry 2000 systems: Together with an MBAD board, provides a link between the MULTIBUS card cage and an optional MULTIBUS expansion unit. An MBIF board is installed in the MULTIBUS card cage and connects the system bus to the MULTIBUS boards that are plugged into the MULTIBUS card cage.
MCMM
See Multi-Chip Memory Module (MCMM).
MDC
See Management and Diagnostics Controller (MDC).
mean time between failures (MTBF)
The average time, expressed in thousands or tens of thousands of hours, that a hardware component will run before requiring service.
media
A collective word for the material--such as floppy or hard disk, CD disc, or tape--on which computer information is stored. See also medium.
media changer device
A backup device that can automatically load tapes into a device. An example of a media changer device is the 3480-Compatible Tape Subsystem, when used with tape magazines.
medium
  1. The material on floppy or hard disks, CD discs, and magnetic tape, on which the signals from the read/write head of the storage device are recorded.
  2. The conductor--such as twisted-pair, coaxial, and fiber-optic cable--used to transfer bits among networked stations.
Media Access Control (MAC)
In networking:
  1. The lower of two sublayers of the Open Systems Interconnection (OSI) model data link layer. The MAC sublayer handles access to shared media, such as whether token passing or contention will be used. See also Logical Link Control..
  2. That part of a data station that supports MAC functions, including framing and deframing data units, performing error checking, and acquiring the right to use the underlying physical medium.
  3. The Data Link Layer responsible for scheduling and routing data transmissions on a shared-medium LAN (for example, an FDDI ring).
See also Open Systems Interconnection (OSI) model.
megabyte (MB)
Roughly a million (2**20) bytes.
megahertz (Mhz)
One million hertz. One hertz is equal to one cycle per second. This unit is often used as a measure of microprocessor clock speed.
memory-allocation pool
In DYNIX/ptx, a data structure used to allocate memory for a specific kernel component. The kmstune command is used to view or tune the attributes and statistics for memory-allocation pools.
Memory Filesystem (MFS)
In DYNIX/ptx: A pageable, memory-based filesystem in which filesystem images are held in virtual memory associated with processes created by the mount process. The contents of the filesystem are lost when it is unmounted or the system is shut down.
memory logical unit (MLU)
Under Construction.
memory management unit (MMU)
Under Construction.
menu
In windowing environments: A list of commands or functions selected with a mouse or other pointer; may lead to a second menu or dialog box with options for further refining the original selection. Many application programs use menus as a means of providing users with an alternative to program commands.
message
  1. In communications: A unit of information transmitted electronically from one device to another.
  2. In STREAMS programming: One or more linked blocks of data with STREAMS control structures that contain message type and other information. A message is the only means of transmitting data within a stream. See also STREAMS.
message block
In STREAMS programming: A structure that transmits data or information, as identified by its message type, in a stream. A message block is made up of three parts: a data buffer with its control structures, an mblk_t structure and a dblk_t structure. See also STREAMS.
Message-Oriented Test Interchange System (MOTIS)
See International Organization for Standardization (ISO), Message Handling System (MHS).
message queue
Messages waiting in line to be processed by the queue's service procedure.
Message Transfer Agent (MTA)
In electronic mail: The equivalent of Mail Transfer Agent. See also Mail Transfer Agent (MTA).
message type
A value that categorizes the content of a message, whether data, control, error, or status information.
metacharacter
  1. Special character (such as the asterisk) used for matching filenames on the command line.
  2. ASCII character with special meaning during pattern processing. Such characters are used to represent single-byte or multibyte character patterns that can be matched during processing.
MEU
See MULTIBUS Expansion Unit (MEU).
Mezzanine board
In the FC Bridge: The electronics assembly that provides the interface circuitry and connectors for SCSI ports 4, 5, 6, and 7. See also bridge in Fibre Channel technology, Small Computer Systems Interface (SCSI).
Mfile
Under Construction.
MFS
See Memory Filesystem (MFS).
MHz
See megahertz (MHz).
MIB
See Management Information Base (MIB).
microprocessor
See central processing unit (CPU).
MILNET (military network)
A large group of interconnected US military computers.
minor number
In UNIX-based operating systems: An identification number that specifies a device, such as a particular terminal or disk, within a device type. See also major number.
MIPS (millions of instructions per second)
A measure of computer-processing speed. See also transactions per second (TPS).
mirroring
  1. (n.) In information-storage hardware: A fault-tolerance technique in which information on a hard disk is duplicated on additional hard disks.
  2. (adj.) In computer graphics: Describing the technique of displaying a mirror image of a graphic.
MLU
See memory logical unit (MLU).
MMU
See memory management unit (MMU).
mnemonic
An easy-to-remember symbol or name for a long or complicated term; for example, "mpy" for "multiply."
modem (modulator-demodulator)
A device that enables computers to send and receive digital data across analog communication lines by translating computer signals into audible tones and vice-versa.
module
  1. In operating-system software: A component or group of components that work together in the kernel to perform a specific function; for example, I/O drivers.
  2. In software programming: A separately compiled program that is part of a larger program.
  3. In networking: A pair of queues that perform functions on messages travelling between stream head and driver.
module configuration file
In the DYNIX/ptx operating system: Each software module in a kernel configuration tree has a mod_config file. The mod_config file specifies what the module is and what other files are needed to generate the module. This file serves as input to the config program. See also system configuration file.
Motif
User interface software, from Open Systems Foundation (OSF), for use with the X Window System.
MOTIS
See Message Handling System (MHS).
mount command
In UNIX-based operating systems: A command for linking a secondary filesystem to the primary filesystem, root, by a mount-point directory, so that the secondary filesystem can reside on a separate storage device or in another disk partition.
mount point
In UNIX-based operating systems: The directory at which a filesystem is mounted under which other filesystems are to be mounted.
MTA
  1. See Mail Transfer Agent (MTA).
  2. See Message Transfer Agent (MTA).
MTBF
See mean time between failures (MTBF).
MTU
See maximum transfer unit (MTU).
MULTIBUS
A much-used interface bus designed by Intel Corporation and standardized as IEEE-796. MULTIBUS adapters, available for Symmetry 2000 systems, make it possible to add devices such as controller boards for printers, terminals, and high-speed communications.
MULTIBUS Expansion Unit (MEU)
The MULTIBUS card cage and interface boards used with the Symmetry 2000/400 and 2000/700 systems and with the S27 and S81 systems.
Multi-Chip Memory Module (MCMM)
Under Construction.
multidrop line
See multipoint link.
multihomed host
  1. In networking: A computer with multiple connections, physical or logical, to one or more networks.
  2. In TCP/IP networking: a host with multiple Internet Protocol addresses. See Internet Protocol (IP).
multimode fiber
A type of optical fiber which incorporates short wave lasers and which is used with Gigabaud Link Modules (GLM). Typically, it is used for links of up to 500 m. See also Gigabaud Link Module.
multiple access unit (MAU)
The central hub to which all token-ring boards must be attached. Also called "passive concentrator.''
multiplexer
  1. A hardware circuit that converts many signals to one or one to many so that the resulting signal or signals can be transmitted; for example, the Symmetry VMEbus Terminal Line Controller board.
  2. In operating systems: A pseudodevice driver that allows messages to be routed to multiple streams in the kernel. A multiplexer supports the processing of interleaved data streams and the processing of inter-network protocols. A lower multiplexer links multiple streams on its downstream side; an upper multiplexer links multiple streams on its upstream side.
multipoint link
In networking: A communication link connecting several stations to the same communication line. Also called a "multidrop line." See also point-to-point link.
multiprocessing
  1. (adj.) Describing a computer system with two or more central processor units (CPUs) operating at once. All Symmetry and IBM NUMA computer systems are multiprocessing. See also symmetric multiprocessing.
  2. (n.) Simultaneous processing by multiple central processing units (CPUs).
Multiprogramming with Virtual Storage
Under Construction.
multiuser mode
In UNIX-based operating systems: An operating system mode in which all users have access to the system. See also single-user mode.
mutual exclusion
In software programming: A multitasking technique that allows only one program at a time to access a resource such as a memory location, I/O port, or file. Often implemented through semaphores.
mux.
See multiplexer.
MVK Switch
Mouse/Video/Keyboard switch. The MVK Switch allows up to eight MVK clients to be served by a single mouse, monitor, and keyboard.
MVS
See Multiprogramming with Virtual Storage (MVS).
mwm
The window manager provided with ptx/XWM.


N

name server
In networking: The server that translates network names to addresses.
name-to-address mapping
In DYNIX/ptx, a facility that enables an application to obtain the address of a network service on a specified machine in a transport-independent manner.
narrow SCSI
An implementation of the Small Computer Systems Interface (SCSI) standard in which up to eight devices, including the initiator or bus controller, can be attached to the SCSI bus. See also Small Computer Systems Interface (SCSI).
National Institute of Standards and Technology (NIST)
Formerly the National Bureau of Standards (NBS), founded in 1901, the National Institute of Standards and Technology was renamed in 1988 and supports industry, commerce, scientific institutions, and all branches of U.S. Government in advancing measurement science and developing standards.
NAU
See network addressable unit (NAU).
NBS
See National Institute of Standards and Technology, NIST.
NCCF
See Network Communication Control Facility (NCCF).
NCK
See Network Computing Kernel.
NCP
See Network Control Program (NCP).
NCP Packet-Switching Interface (NPSI)
In SNA networking: A program that acts as an interface between the network control program (NCP) and an X.25 network. See also Network Control Program (NCP), X.25.
NCS
See Network Computing System.
negotiable BIND
See BIND type.
netlsd
The string used to invoke the network license management daemon. See also license management daemon.
netmask
In networking: A 32-bit IP address is divided into a network portion and a host portion. The network portion, expressed in hexadecimal notation, is called the "network mask" or simply "netmask." Subnetting increases the number of bits in the netmask, allowing many subnetworks for each logical network. Also called "address mask" or "subnet mask." See also subnetting.
network
  1. An interconnected group of nodes (computer systems, terminals, and other equipment) among which information is passed.
  2. The collection of equipment through which connections are made between nodes.
network address
  1. In networking: A network layer address referring to a logical, rather than a physical, network device.
  2. In SNA networking: An address that consists of subarea and element fields and identifies a link, link station, or network addressable unit (NAU). Subarea nodes use network addresses; peripheral nodes use local addresses. The boundary function in the subarea node to which peripheral nodes are attached transforms local addresses to network addresses and network addresses to local addresses. See also network addressable unit (NAU).
network addressable unit (NAU)
In SNA networking: Any device on the network that has a network address, including logical units (LUs), physical units (PUs), and system service control points (SSCPs). See also logical unit (LU), physical unit (PU), and system services control point (SSCP).
Network Communication Control Facility (NCCF)
Under Construction.
Network Computing Kernel (NCK)
In network computing: The runtime components of the Network Computing System (NCS). These components include the Remote Procedure Call (RPC) runtime library and the Location Broker. NCK contains all the software needed to support a distributed application.
Network Computing System (NCS)
In network computing: A set of software components, developed by Apollo Computer Inc., that conform to the Network Computing Architecture. These components include the Remote Procedure Call (RPC) runtime library and the Location Broker.
Network Control Program (NCP)
In SNA networking: A program that controls the operation of a communication controller. The program is generated by the user from a library of IBM-supplied modules.
Network File System (NFS)
One of a suite of protocols developed by Sun Microsystems that allow remote file access across a network.
Network Information Center
In networking: An organization at SRI International that provides information about TCP/IP and the Internet. NIC assigns Internet addresses and acts as the repository for all Requests for Comments (RFCs) and TCP/IP documentation and policies. See also Request for Comments (RFC), Transmission Control Protocol/Internet Protocol (TCP/IP).
network layer
In OSI network architecture: The Open Systems Interconnection (OSI) model layer that provides functions and procedures for transferring data across the network, independent of both the media and topology of underlying subnetworks. See also Open Systems Interconnection (OSI) model.
Network Layer Interface (NLI)
Under Construction.
network license server
See license management daemon.
Network Logical Data Manager (NLDM)
In SNA networking: A network management product, developed at IBM, that collects information about sessions and routes for troubleshooting. NLDM runs under NCCF. See also Network Communication Control Facility (NCCF).
network mask
See netmask.
Network Problem Determination Application (NPDA)
In SNA networking: a network management product, developed at IBM, that helps troubleshoot the network online.
network service access point (NSAP)
In networking: A network address, as specified by ISO. An NSAP is the point at which OSI Network Service is made available to a transport layer (Layer 4) entity. See also Open Systems Interconnection (OSI) model.
network service data unit (NSDU)
Under Construction.
NFS
See Network File System (NFS).
NIC
See Network Information Center (NIC).
NIST
See National Institute of Standards and Technology (NIST).
NLDM
See Network Logical Data Manager (NLDM).
NLI
See Network Layer Interface (NLI).
node
  1. In networking: A point capable of sending and receiving data. A node is either a device, such as printer or workstation, or a storage location on a disk.
  2. The SNA device in which layer services are implemented, whether with hardware or software.
  3. In IBM's NUMA systems: One or more Quads running a single instance of the operating system.
  4. In ptx/CLUSTERS: A single member of a cluster. A node may be a complete computer or one or more Quads, running their own copy of the operating system. See also cluster.
nodelocked file
In ptx/LICENSE: The text file at a user node (rather than at a license server node) where nodelocked licenses are added.
nodelocked license
In ptx/LICENSE: A type of license that allows the licensed product to be used only at a specified node.
node name
In networking: The name by which a device is known within a network; typically the same as the system name.
nonstandard VTOC
In DYNIX/ptx: A VTOC (Volume Table of Contents) altered for local use. See also Volume Table of Contents (VTOC).
nonswitched line
See dedicated line.
nonuniform memory access (NUMA)
In computer hardware: A type of shared-memory architecture in which blocks of memory are distributed among two or more processors instead of being contiguous in one physical location.
nopriv disk
A ptx/SVM disk consisting of a data partition that is not paired with a type-8 partition, and which therefore contains no private area for storing configuration database information.
Notify
In SNA networking: A request unit (RU) sent by a system services control point (SSCP) to let a logical unit (LU) know the status of a requested procedure. See also logical unit (LU), request/response unit (RU), system services control point (SSCP).
NPDA
See Network Problem Determination Application (NPDA).
N_port
A hardware entity which includes a Link_Control_Facility. It may act as an Originator, Responder, or both. An N_Port usually connects to an F_Port of a fabric, but pairs of N_Ports can be directly connected over a point-to-point channel. See also Link_Control_Facility.
NQuad
A 4-processor building block server that runs Microsft Windows NT. The NQuad is manufactured by Intel Corporation.
NSDU
See network service data unit (NSDU).
NSAP
See network service access point (NSAP).
NSDU
See network service data unit (NSDU).
null string
A string containing no characters. Also called "empty string."
NUMACenter
One or more Enterprise cabinets containing SQuads or Quads and NQuads or P6-based SHV Quads. The SQuads and Quads run DYNIX/ptx; the NQuads and P6-based SHV Quads run Windows NT.
NUMACenter Director
NUMA Center Director is a Web-based systems management application layered on top of IBM Netfinity Director and Tivoli IT Director. NUMACenter Director integrates several systems management software applications to provide a single Web-based systems management framework.
IBM NUMA-Q
IBM's implementation of a Nonuniform Memory Access (NUMA) system architecture, using Intel's Quad processor components.


O

object
  1. In object-oriented programming: A data structure in memory that can comprise both procedures and data as a single discrete entity. Each object has a set of descriptors defining its type and its capabilities. Objects communicate with each other by passing messages.
  2. In computer graphics: A distinct entity. For example, a bouncing ball in a computer-graphics program is an object.
object-oriented
Describing a computer system or programming language that supports objects. See also object.
OCR
See optical character recognition (OCR).
octal notation
The base-8 numbering system.
OFC
See Open Fibre Control.
offline
Describing the operation of a functional unit without the continual control of a computer.
OLR
See online replacement (OLR).
OLTP
See online transaction processing (OLTP).
online
  1. Describing the operation of a functional unit under the continual control of a computer.
  2. Describing a user who has accessed a computer through a terminal.
online documentation
Electronically rendered information about a computer or other electronic system or about the software that runs on it. Typically, online documentation is either directly available from the user interface, as with online help, or easily retrievable from a network or storage medium.
online replacement (OLR)
The capability of removing, installing, or replacing components of a computer system during normal operation. Disk drives in the QCIC subsystem have OLR capability.
online transaction processing (OLTP)
The processing of transactions as they are received by the computer. Master files are updated as soon as transactions are entered at terminals or received over communications lines.
Open Fibre Control (OFC)
To meet Class 1 laser-safety requirements, first-generation optical transceiver devices using certain laser-diode power levels are required to have open fiber-link detection and automatic laser shutdown circuits. Optical transceivers with these features are called OFC devices. Second-generation devices use lasers at lower power levels and do not need OFC to meet Class 1 certification requirements. These kinds of devices are called non-OFC.
open procedure
The module routine called when a module is pushed onto a stream or the driver routine called when a driver is opened.
open subroutine
In software programming: A program module that is copied, repeatedly if necessary, wherever it is needed in a program. See also closed subroutine.
Open Systems Interconnection (OSI) model
The layered architecture, developed by ISO, that standardizes the interaction and levels of service for computers on a communication network. The OSI model consists of seven layers--Application, Presentation, Session, Transport, Network, Data Link, and Physical--with each layer building upon the layer below it. See also International Standards Organization (ISO).
operating system
Software that controls the execution of programs on a computer system, providing such services as resource allocation, scheduling, input/output control, and data management.
optical character recognition (OCR)
The process of scanning or reading printed characters on paper and translating them into computer text. OCR can be performed by standard optical scanners and specialized software, or, in some cases, by special automated readers.
optical loopback plug
A short section of optical fiber housed in a connector that provides a loopback connection between the transmit and receive ports of a Gigabaud Link Module (GLM). See also Gigabaud Link Module (GLM).
option
In UNIX-based operating systems: An element of a command line, usually preceded by a hyphen, that modifies how the command operates. For example, the ls command produces a simple listing of files in a directory; the ls command with the -l option produces a listing of files accompanied by information about each file, such as its size and the access permissions applied to it.
ordinary file
In UNIX-based operating systems: A collection of logically related bytes, treated as a unit by the operating system. An ordinary file contains text, program code, or other information.
originator
A Fibre Channel logical function associated with an N_port responsible for originating an exchange. See also responder, N_port, Fibre Channel.
Orion chip set
A central building block of Intel's Quad processor, used in IBM's NUMA-Q computer systems. See also Quad, NUMA-Q.
OSI model
See Open Systems Interconnection (OSI) model.
ordinary file
Access that uses a connection specifically for management access. Usually, but not always, this interface has little or no access to customer services or data.
output
  1. The end product of computation.
  2. The response the system generates when a command is issued. By default, output is displayed on the terminal screen, but it can be redirected to a file or another program.
owner
In UNIX-based operating systems: The user name associated with a file. The owner and the superuser control access to the file. See also superuser.


P

PA key (program attention key)
On a display-device keyboard, a key that produces an interruption to solicit program action. See also PF key (program function key).
pacing
In SNA networking: IBM's term for "flow control," a technique by which a receiving component controls the rate of transmission of a sending component to prevent overrun and congestion. See also session limit.
packet
In networking: A group of bits that has a defined format and fixed maximum size, sent as a unit across a network.
packet assembler/disassembler (PAD)
In networking: A hardware or software device for splitting an X.25 data stream into discrete packets for transmission over some medium and then reforming the stream at the receiver. See also X.25.
packet-switched data network (PSDN)
In networking: In Europe, the U.K., Canada, Australia, and New Zealand, an X.25 network that offers a viable alternative or supplement to the public switched telephone network. See also X.25.
packet-switched stream (PSS)
Under Construction.
packet switching
The process of routing and transferring data by means of addressed packets so that a channel is occupied only during the transmission of a packet. Upon completion of the transmission, the channel is made available for the transfer of other packets.
packet-type identifier (PTI)
Under Construction.
PAD
See packet assembler/disassembler (PAD).
page
A fixed-length segment of data or of a program treated as a unit in storage allocation. See also page fault, paging.
page fault
An error that results when reference is made to an address on a page that is not in main storage. Excessive page faults degrade system performance. See also page, paging.
paging
A storage-allocation technique in which programs or data are divided into fixed-length segments, or pages, main storage is divided into page frames of the same length, and pages are transferred between main and auxiliary storage as needed. See also page, page fault
panic
A condition in which the kernel stops executing correctly and hangs, stops, or crashes, usually as a result of a nonrecoverable error.
parameter
  1. In RJE BSC: an identifier, such as OUTPUT PATH, whose value specifies a particular aspect of the RJE BSC environment. A series of parameters makes up a profile keyword.
  2. In software programming: A value or reference passed to a function, procedure, subroutine, command, or program by the caller.
See also argument.
parent directory
The directory immediately above a given directory in the filesystem structure. In a fully specified pathname, the directory to the left of a given directory. In a relative pathname, the directory represented by two dots (..). See also pathname.
parm
Abbreviation for parameter.
parse
In UNIX-based operating systems: To analyze the elements of a command line and, from that information, to build a parameter list for the command processor.
partial plex
In ptx/SVM: A mirror that is only as large as the subdisk(s) to be mirrored.
partition
A portion of the available storage space on a disk.
password
A unique string of characters that a program, computer operator, or user must supply to meet security requirements before gaining access to data.
password aging
In UNIX-based operating systems: A security feature by which the superuser can specify how often users must change their passwords. See also superuser.
Path Control layer
In SNA networking: The functional layer that provides services controlling the route taken by data as it moves through the network. See also Systems Network Architecture (SNA) functional layers.
Path Control Network
In SNA networking: The functional layer that includes the Data Link Control and Path Control layers. See also Systems Network Architecture (SNA) functional layers.
pathname
A name identifying the unique path through the directory tree from the root directory to a specific directory or file. A full (fully specified) pathname begins with the root directory; a relative pathname begins with the current directory (..).
Pbay
Abbreviation for "SCSI peripheral bay." A rack-mounted enclosure in earlier IBM NUMA systems' expansion cabinets and the larger system cabinets, it provides mechanical mounting, power, cooling, and SCSI connections for disk and tape drives. All these peripheral devices plug into the Pbay backplane, for easy installation and replacement. Superseded by the Bootbay subsystem in more recent IBM NUMA systems.
Pbay monitor board
A circuit board that incorporates circuitry for monitoring Pbay cooling fans, controlling power output to the Pbay disk drives, and controlling the drives' indicators. The SCSI bus runs from the QCIC board, through the Pbay monitor board, to the Pbay backplane, where it is distributed to the disk drives in the Pbay. Responding to commands on the SCSI bus, the monitor board switches the power on or off to individual disk drives and controls their indicators.
PCI bus
See Peripheral Component Interconnect (PCI) bus.
PDN
See public data network (PDN).
PDU
See protocol data unit (PDU).
peer
In network architecture: Any functional unit in the same layer as another functional unit. See also Open Systems Interconnection (OSI) model.
Peripheral Component Interconnect (PCI) bus
A high-performance bus for interconnecting highly integrated peripheral-controller components, peripheral add-in boards, and processor and memory systems.
Peripheral Interface Controller (PIC)
An IBM integrated circuit used in the System Services Module (SSM). The PIC provides a data path and performs byte packing and unpacking. On the SSM, one PIC transfers data between the VMEbus and the system bus, while the other transfers data between the system bus and the SSM central processing unit (CPU) or the SCSI bus.
Peripheral Interface Controller - Wide (PICw)
An enhanced version of the PIC with 32-byte data buffers instead of the16-byte buffers used in the original PIC. See also Peripheral Interface Controller (PIC).
peripheral node
In SNA networking: A node that uses local addresses and therefore is not affected by changes to network addresses.
peripheral node control point (PNCP)
Under Construction.
permanent virtual circuit (PVC)
A virtual circuit that is permanently established. The PVC saves bandwidth associated with establishing and tearing down circuits in situations where certain virtual circuits must exist all the time. In ATM terminology: "permanent virtual connection." Compare with switched virtual circuit (SVC)
permission
The level of availability (read, write, execute) of a file permitted a given user. The superuser or the owner of a file assigns these permissions for the owner, the owner's group, and all other users. See also superuser.
PF key (program function key)
On a display device keyboard, a key that passes a signal to a program to call for a particular display operation. See also PA key (program attention key).
Physical Control layer
In SNA network architecture: The functional layer that provides services for electrical and physical connections in the network. See also System Network Architecture (SNA) functional layers.
Physical layer
In the OSI network architecture, the layer that provides the electromechanical interface to the communications media; often referred to as layer 1. See also Open Systems Interconnection (OSI) model.
physical path specifier
In DYNIX/ptx: the physical hardware path to a SCSI device. Physical path specifiers are used to locate devices at boot time before the naming database is available.
physical unit (PU)
In SNA networking: The component that manages and monitors the resources of a node--such as links and link stations--as requested by an SSCP in an SSCP-to-SSCP session. See also system services control point (SSCP).
PIC
See Peripheral Interface Controller (PIC).
PICw
See Peripheral Interface Controller - Wide (PICw).
PID
See process identifier (PID).
pinout
A diagram or table showing the signal or voltage level for each pin or contact on a given connector or integrated circuit. The term may also be applied to a diagram for two connectors, showing which pins must be connected to construct a cable.
PIP
See program initialization parameter (PIP).
pipe
In UNIX-based operating systems: A connective symbol (|) used between two commands on a command line, indicating that the output from the preceding command is to be used as the input for the following command. See also pipeline.
pipeline
Two or more commands linked by a pipe. See also pipe.
plex
In ptx/SVM: A logical component of a ptx/SVM volume, holding one instance of a set of data that may be physically distributed over different physical disk partitions and drives. Plexes are in turn composed of one or more subdisks. See also subdisk, volume.
PLU
See primary logical unit (PLU).
PNCP
See peripheral-node control point (PNCP).
point-to-point link
In networking: A communication link connecting one station to another. See also multipoint link.
pop system call
In network programming for UNIX-based systems: A STREAMS ioctl system call that causes the module immediately below the stream head to be removed (or "popped") from a stream. See also buffer, ioctl system call, push system call.
port
  1. (n.) The connection through which interaction between the computer and peripheral devices takes place. The IBM NUMA-Q Fibre Channel Subsystem has F-ports and N-ports. See also fabric, F_port, node, and N_port.
  2. (v.) To adapt a program written on one computer or operating system to run on another.
Portable Operating System Interface for UNIX (POSIX)
In programming for UNIX-based systems: A set of standard UNIX features and characteristics defined by IEEE.
POSIX
See Portable Operating System Interface for UNIX (POSIX).
Postal, Telephone, and Telegraph (PTT)
A government agency that provides local and long-distance telephone services. PTTs provide such services in most areas outside of North America.
power up
To apply electrical power to a computer.
Power-Up Monitor
A terminal for Symmetry systems that runs tests, initializes devices, and carries out other procedures necessary to bring up the operating system.
PPC Board
See Parallel Printer Controller (PPC) Board.
pragma
A standardized form of comment which has meaning to a compiler. It may use a special syntax or a specific form within the normal comment syntax. A pragma usually conveys non-essential information, often intended to help the compiler to optimise the program.
preallocation
In ptx/EFS: The assignment of space for a file so that disk blocks will be physically part of a a file before they are needed. Enabling an application to preallocate space for a file guarantees that a specified amount of space will be available for that file, even if the filesystem is otherwise out of space. See also reservation.
preferred plex
In ptx/SVM: A plex read policy whereby one plex is designated as the "preferred" plex for reads.
Presentation layer
In OSI network architecture: The layer that adds structure to the units of data. See also Open Systems Interconnection (OSI) model
presentation-service access point (PSAP)
Under Construction.
presentation space, altered (PSA)
Under Construction.
primary half-session
In SNA networking: the half-session that sends the session activation request. See also primary logical unit (PLU), secondary half-session.
primary logical unit (PLU)
In SNA networking: The logical unit (LU) that sends the Bind session request for a particular LU-to-LU session. See also Berkeley Internet Name Domain (BIND), logical unit (LU).
print control character
A nonprinting character (such as line feed, page feed, and carriage return) that must be interpreted by the printer.
printer
A peripheral device that prints text or graphics.
printer class

In LP Print Service: A grouping of printers, created by the system administrator, that serves to distribute print requests. Upon receiving a print request, the first available printer in the group prints it. See also print request.

printer, destination
See destination printer.
printer filter
A program that performs tasks such as detecting printer faults and converting a file to print properly on a specific printer.
printer interface program
In the LP Print Service: A program that prepares print requests for a particular kind of printer; for example, by supplying control characters and escape sequences.
print request
A request created when a user issues the lp command. The request includes the files to be printed and any options specified on the lp command line. See also printer class, print request ID.
print request ID
In UNIX-based operating systems: A number identifying a print request. Print request ID can be used to check the status of a request, cancel a request, or send a request to another printer or printer class. See also printer class, print request.
print-service interface program
See printer interface program.
private objects
ptx/SVM objects (subdisks, plexes, and volumes) that can be used only on the node on which they were created.
private region
A region of a physical disk that is used to store private, structured, ptx/SVM information.
process
In UNIX-based operating systems: An instance of a program executing on a system.
process accounting
In UNIX-based operating systems: A set of programs that accumulate accounting records and produce summary information.
process identifier (PID)
In UNIX-based operating systems: The number by which the kernel identifies a process.
processor
See CPU (central processing unit).
product ID
In ptx/LICENSE: An integer that identifies a vendor's licensed software product; by means of product IDs, the license server distinguishes among products of the same vendor.
product password
In ptx/LICENSE: A string encoded with information about licenses for a software product. Product passwords are of two types: license passwords and compound passwords. See also license password, compound password
profile
A file that defines the environment in which BSC RJE is being run. BSC RJE is composed of several profiles. See also Remote Job Entry (RJE), Binary Synchronous Communications (BSC).
.profile file or profile file
A start-up file for Bourne shell or Korn shell in which environment variables and commands are used to modify the environment.
program
A file containing instructions the computer executes in performing a task.
program initialization parameter (PIP)
In IBM's Systems Network Architecture (SNA): Initialization information exchanged between two transaction programs belonging to the same logical unit (LU). See also logical unit (LU).
Prolog (Programming in Logic)
A high-level programming language used in the development of applications for artificial intelligence.
PROM (programmable read-only memory)
A type of memory chip that can retain its contents without electricity. See also electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), flash PROM.
prompt
Displayed text indicating that a computer program is waiting for input.
protocol
See communications protocol.
protocol data unit (PDU)
In OSI networking: OSI term for ''packet.'' See also Open System Interconnecton (OSI) model, packet.
protocol module
A module written to comply with industry-standard service interfaces.
protocol port
In ptx/TCP/IP networking: An abstract destination point identified by a positive integer. Each protocol port supports a different service. Some port numbers, called well-known ports, are assigned permanently to services. The remaining ports are used arbitrarily by ptx/TCP/IP. See also well-known port.
PSA
See presentation space, altered (PSA).
PSAP
See presentation-service access point (PSAP).
PSDN
See packet-switched data network (PSDN).
pseudodevice
In UNIX-based operating systems: A virtual device. It is not physically present but is treated like hardware by the operating system; for example, a pseudo-TTY.
pseudodevice driver
A software driver, not directly associated with a physical device, that performs functions internal to a stream. Multiplexors and error or trace loggers are pseudodevice drivers.
PSS
See packet-switched stream (PSS).
PTI
See packet-type identifier (PTI).
PTO
See public telecommunication operator (PTO).
PTT
See Postal, Telephone, and Telegraph (PTT).
ptx/SVM disk
An entire unpartitioned disk or single disk partition that is both under ptx/SVM control and is assigned to a disk group.
PU
See physical unit (PU).
public data network (PDN)
A network operated by a government (as in Europe) or private organization to provide computer communications to the public, usually for a fee. With a PDN, a small organization can create a WAN without incurring the equipment costs of long-distance circuits.
public directory
In UNIX-based operating systems: A directory that can be used by anyone on the system. Typically/tmp and /usr/tmp are public directories used for temporary file storage. The UUCP system provides a public directory named /usr/spool/uucppublic, where users from remote systems can deposit files.
public region
A region of a physical disk managed by ptx/SVM that contains available space and is used for allocating subdisks.
public telecommunication operator (PTO)
Under Construction.
push system call
In network programming for UNIX-based systems: A STREAMS ioctl system call that causes a module to be inserted (or "pushed") onto a stream immediately below the stream head. See also buffer, ioctl system call, pop system call.
put procedure
In UNIX-based operating systems: The queue routine that receives messages from the preceding queue. The put procedure is the single entry point into a queue from a preceding queue. The procedure may perform processing on the message; it then either links the message to the message list of the queue for subsequent processing by a service procedure or passes the message to the put procedure of the following queue. See also buffer, queue.

Q

QBB
See Quad Base Board (QBB).
QCIC Board
See Quad-Channel I/O Controller (QCIC) Board.
QCIC Subsystem
The collective name for a QCIC, QCIC-W, or QCIC-E board, and its attached Pbays, disk drives, cables, and other components.
QLLC
See qualified logical-link control (QLLC).
QLLC exchange identification (QXID)
Under Construction.
QOS
See quality of service (QOS).
QOS parameters
See quality of service (QOS) parameters.
QPC
See Quad Processor Card (QPC).
Quad
The basic building block for all IBM NUMA systems. A Quad is a self-contained, rack-mount unit that includes four processors, memory, I/O and communications boards, and a system-management controller. It also contains and optional IQ-LINK board for connecting with other Quads. See also Management and Diagnostics Controller (MDC), IBM NUMA-Q, and IQ-Link.
Quad Base Board (QBB)
Under Construction.
Quad-Channel I/O Controller (QCIC) Board
A four-channel, differential SCSI-2 controller board that connects to the Symmetry system bus. The QCIC board can control up to six disk drives residing in Pbays on each channel, for a total of 24 disk drives per board.
Quad Processor Card (QPC)
Under Construction.
qualified logical-link control (QLLC)
Under Construction.
quality of service (QOS)
In networking: A measure of performance for a transmission system that reflects its transmission quality and service availability.
quality of service (QOS) parameters
In ATM networking: Parameters that control the amount of traffic the source router sends over a switched virtual circuit (SVC). If any switch along the path cannot accommodate the requested QOS parameters, the request is rejected, and a rejection message is forwarded back to the originator of the request. See also switched virtual circuit (SVC)
queue

In network programming for UNIX-based systems: The component of a module that performs functions on messages passing through the module. Each module has two queues: a read queue passing messages upstream and a write queue passing messages downstream. The read queue contains the open and close procedures for the module. A queue typically contains put and service procedures, a message list, and private data. See also buffer, pop system call , push system call, put procedure.

queuing
In network programming: The programming technique for handling data or messages awaiting transmission.
QXID
See QLLC exchange identification (QXID).