R

RAM
See random-access memory (RAM).
random-access memory (RAM)
Semiconductor-based memory for temporary storage. See also read-only memory (ROM).
RARP
See Reverse Address Resolution Protocol.
raw device
In UNIX-based operating systems: A block device that handles data as a stream of bytes, rather than as a block. Programs such as fsck and volcopy use disk and tape drives as raw devices.
RDBMS
See relational database management system (RDBMS).
read-only memory (ROM)
Semiconductor-based memory for permanent storage. See also random-access memory (RAM).
read permission
In UNIX-based operating systems: On a directory, the ability to list contents (as with the ls command). On a file, the ability to read contents (as with the cat command). See also write permission.
read queue
In UNIX-based operating systems: The queue in a module or driver containing messages moving upstream. The read queue is associated with a read(2) system call and input from a driver.
reboot
To start a computer system after a shutdown or halt. This procedure reinitializes the state of the operating system.
receiver
An electronic circuit that converts a signal from the media (optical or electrical) to an electrical retimed serial logic signal.
record
  1. A collection of data handled together in transfers to and from peripheral devices. The collection of data transferred as a unit is called a "physical record." The collection of data related to one subject is called a "logical record." See also record length.
  2. A data structure made up of fields, each with its own name and type. The elements of a record are accessed by name.
record length
The number of bytes or words in a record. See also record.
recursive
In programming: Descriptive of a self-invoking function (that is, a function that contains a reference to itself).
recycle
In ptx/SVM: To reinitialize a volume without changing its volume name. Recycling removes all entries for that volume from the file and media indexes.
redirection
The process of changing either the source for command input or the destination for command output.
refresh
(n) The process of repeatedly producing an image on a display so that the image remains visible.

(v) To update a visual image on a display or (by extension) a program image in system memory.

Registered Private Operating Agency (RPOA)
In X.25 networking: A category of routing information in the X.25 packet-switched networking standard. It identifies the telecommunications service supplier that provides a particular subnet on an X.25 network.
regular expression
In UNIX-based operating systems: A pattern used by programs such as ed, vi, grep, more, and pg to locate specific character strings in a file. A regular expression can contain special characters that match groups or ranges of characters.
relational database management system (RDBMS)
A software package for the storage and control of logically related data. The data is stored in structures that facilitate the definition and manipulation of references among entries.
relative pathname
See pathname.
relay
In local area networking: A generic term for the equipment that connects separate local-area networks (LANs). See also local-area network (LAN).
reliable transfer service (RTS)
Under Construction.
reliable transfer service element (RTSE)
Under Construction.
remote access
In computer networking: Communication with a data-processing facility by means of a data link.
remote job entry (RJE)
In IBM's Binary Synchronous Communications (BSC) architecture: A batch-oriented rather than interactive mode of computing over a network. In an RJE environment, jobs are submitted to a remote host computer, and output is received later.
remote login
The service that allows users on one system to log in to another system on the network and interact with the remote system as if their terminals were directly connected to it.
remote method invocation (RMI)
A communication protocol that enables the creation of distributed Java-to-Java applications, in which the methods of remote Java objects can be invoked from other Java virtual machines, possibly on different hosts. A method invocation on a remote object has the same syntax as a method invocation on a local object.
remote operation
An action invoked by one application entity but performed by another.
remote-operations service element (ROSE)
In OSI networking: The remote procedure call (RPC) mechanism used by various OSI network application protocols. See also remote procedure call (RPC).
remote procedure call (RPC)
A high-level mechanism that enables programs on networked platforms to communicate with local or remote resources.
repeater
In local area networking (LAN): A device that copies signals from one station to another.
repertoire
A character set required by computer-to-computer communication; for example, ASCII or EBSIDIC.
repertoire assignment
A method for two computers to agree, at connection, upon a common character set; for example, ASCII or EBSIDIC.
request primitive
The primitive passed from the DLS (data link service) user to the DLS provider to request that a service be initiated. See also data link service (DLS).
request/response header (RH)
In SNA networking: Control information preceding a request/response unit (RU), specifying the type of RU (request unit or response unit) and containing control information associated with that RU. See also request/response unit (RU).
request/response unit (RU)
In SNA networking: A request or response unit. A request unit may contain control information (such as a request code); it may instead contain function-management (FM) headers, end-user data, or both. A response unit acknowledges a request unit; it may contain prefix information received in a request unit. A positive response unit may contain additional information (such as session parameters in response to BIND SESSION); a negative response unit contains "sense data" defining the exception condition.
Request to Send (RTS)
A signal sent by the data terminal equipment (DTE) to the data communications equipment (DCE), notifying it that the DTE has data to transmit. See also data communications equipment (DCE), data terminal equipment (DTE).
Request for Comments (RFC)
A series of numbered Internet informational documents and standards widely followed by commercial software and freeware in the Internet and UNIX communities. Few RFCs are standards, but all Internet standards are recorded in RFCs.
reservation
In ptx/EFS: An extent attribute that specifies how much space is preallocated for a file. See also preallocation.
reserved port
See well-known port.
resilvering
How ptx/SVM makes data on new plexes that are being added to a volume consistent with other existing plexes already attached to the volume.
resource
  1. Any facility of the computing system or operating system required by a job or task; includes main storage, input/output devices, the processing unit, data sets, and control or processing programs.
  2. In ptx/XWM: Application options that specify such attributes as color, font, and behavior. Resources can be set on the command line when a client application is started, or specified in a resources file (usually .Xdefaults in the user's home directory). In the latter case, they are read by clients at start-up, and may also be loaded and stored in the display server program. Also called ''X resources'' and ''X defaults.''
resource domain
One or more FC-connected storage subsystems and the fabric or fabrics common to them. Resource domains can have single or dual fabrics.
resource manager
An interface and associated software providing application access to a system resource, such as a line printer or a DBMS.
respawn
In UNIX-based operating systems: To continuously restart a process after it has exited. This method is used to make TTY lines available for logins after users have logged out.
responder
The process which enables a host system to communicate with one or more initiators. In Fibre Channel technology: A Fibre Channel logical function in an N_port responsible for supporting the exchange initiated by the originator in another N_port. See also N_port, originator.
response primitive
In OSI networking: The primitive passed from the data link service (DLS) provider to the DLS user to acknowledge reception of a previous indication and to convey the desired action of the DLS provider in reponse to the previous indication. See also data link service (DLS) provider, data link service (DLS) user.
restore
To recover files, directories, or filesystems from a backup medium.
resynchronization
How ptx/SVM keeps data on mirrored plexes consistent. Resynchronization is the process by which ptx/SVM updates an already-attached plex that may contain valid, but slightly out-of-date, data.
Reverse Address Resolution Protocol (RARP)
In TCP/IP networking: A protocol by which a diskless machine can obtain its IPaddress from a RARP server. The diskless machine broadcasts a request and its physical hardware address. The RARP server responds by returning an IP address based on the physical address. See also BOOTstrap Protocol.
revision text
See version identifier.
RFC
See Request for Comments.
RH
See request/response header.
RIP
See Routing Information Protocol.
RJE
See remote job entry (RJE).
RMI
See remote method invocation
RMS
See VMS Record Management System (RMS).
Rock Ridge Interchange Protocol (RRIP)
An extension of the ISO-9660 format for CD-ROM that provides support for POSIX filesystem semantics, including UNIX-style filenames, file types, file permissions, and directory hierarchies.
rolling upgrade
In clustered systems: Updating the system software on a cluster without interrupting service to the users of the cluster.
ROM
See read-only memory (ROM).
root
In UNIX-based operating systems: The account name of the superuser, who has access to all files and directories and is the owner of most system files.
root device
In UNIX-based operating systems: The disk drive on which the root partition resides.
root directory
In UNIX-based operating systems: The source of the filesystem, represented by a slash (/).
root filesystem
In UNIX-based operating systems: The first filesystem in the operating system. It begins with the root directory and contains several system directories as well as the operating system kernel.
root login
See root.
root partition
In UNIX-based operating systems: The disk partition that contains the root filesystem.
ROSE
See remote-operations service element (ROSE).
rotational delay
In data-storage hardware: The time it takes a disk to rotate so that, once the disk drive has moved the head, the data is under the head and over the right track.
round-robin
Describing an activity that occurs in a set, cyclic order among a group of devices or programs. For example, bus access is granted to Symmetry system boards on a round-robin basis (within a high- or low-priority group).
route
The path that network traffic takes from the source to the destination.
router
A relay that stores and forwards data packets directly addressed to it by user systems. The router and the source and destination systems must all adhere to a common routing protocol.
Routing Information Protocol (RIP)
A protocol used to exchange routing information among systems on a small network. The protocol is implemented through a daemon called routed.
RPC
See remote procedure call (RPC).
RPOA
See Registered Private Operating Agency (RPOA).
RRIP
See Rock Ridge Interchange Protocol (RRIP).
RS-232-C
A 25-wire electrical interface for serial communication between a computer and a peripheral device; defined by EIA Standard RS-232.
RTS
  1. See Request to Send (RTS).
  2. See reliable transfer service (RTS).
RTSE
See reliable transfer service element (RTSE).
RU
See request/response unit (RU).
run queue
In DYNIX/ptx, one or more CPUs that execute assigned processes in accordance with the priority and attributes specified by the system administrator.
run level
In the DYNIX/ptx operating system: one of several states of the computer system, each appropriate for different sets of operational or maintenance activities, such as single-user mode or multiple-user mode.
run limit
The maximum number of jobs that can execute simultaneously. Run limits apply to batch and pipe queues, batch queue complexes, and globally to all batch jobs. These limits are set by the system administrator.
run time
The time during which a program is running.


S

SA
See system administrator.
SAK
See stand-alone kernel.
SAP
See service access point.
SAR
See segmentation and reassembly (SAR).
Scalable Coherent Interconnect (SCI)
Standard for internal processor-memory connections within computers, based on the IEEE standard for Scalable Coherent Interface (SCI), IEEE Std 1596-1992. A variant is used to implement cache coherence in IBM NUMA systems. SCI-connected processors do not have to use I/O operations to communicate; they can use ordinary load and store instructions to directly access one another's memory.
Scan Interface Controller (SIC)
An application-specific integrated circuit (ASIC) for controlling scan and clock functions. See also application-specific integrated circuit (ASIC).
SCB
See string control byte (SCB).
SCC
See Synchronous Communications Controller (SCC).
SC-style connector
In IBM NUMA hardware: A rectangular, keyed connector that houses the end of an optical fiber. The connector mates to the receptacle of a Gigabaud Link Module (GLM) Gigabit Interface Converter, or Gigabit Optical Transceiver. SC stands for Subscriber Connector. It has different configurations depending on whether the optical devices and cables are multimode or single mode.. See also Gigabaud Link Module, Gigabit Interface Converter, and Gigabit Optical Transceiver.
SCC-V
See Synchronous Communications Controller - VMEbus (SCC-V).
SCED Board
See SCSI/Ethernet/Diagnostics (SCED) Board.
schedule
In STREAMS programming: To place a queue on the internal list of queues that will subsequently have their service procedure called by the STREAMS scheduler.
SCI
See Scalable Coherent Interconnect.
SCI Cache Link Interface Controller (SCLIC )
An application-specific integrated circuit (ASIC) that connects the SCI to the IQ-Link board in each node. See also application-specific integrated circuit (ASIC), Scalable Coherent Interface (SCI).
SCS
See Systems Network Architecture (SNA) character string.
SC-style connector
In IBM NUMA hardware: A rectangular, keyed connector that houses the end of an optical fiber. The connector mates to a receptacle of a gigabaud link module (GLM).
SCSI
See Small Computer Systems Interface (SCSI).
SCSI disk
A 3.5-inch or 5.25-inch fixed-media device with an integrated controller which connects to the SCSI bus.
SCSI/Ethernet/Diagnostics (SCED) Board
A circuit board required in the S27, S81, and S2000/400, and optional in the Symmetry 2000/700. The SCED provides S27 and S81 systems with system initialization, bus services, diagnostic control, power-supply monitoring, and battery-backed clock. The SCED includes an asynchronous SCSI bus, an Ethernet port, and two serial ports. The SCED may be used in S2000/400 and S2000/700 systems to provide an Ethernet interface. See also Small Computer Systems Interface (SCSI).
SCSI Expansion Cabinet (SEC)
In S2000 systems hardware: A small expansion cabinet used with the SCSI-V board to provide more disk drives for the S16 and S2000/2x0 systems. See also Small Computer Systems Interface (SCSI).
SCSI Peripheral Bay
See Pbay.
SCSI/Processor Interconnect (SPI)
An integrated circuit used in SCSI controller boards. The SPI is used to control the access of the controller board's local processor to memory on the Symmetry System bus, and of system CPUs to the controller board's local memory. See also SCSI/Processor Interconnect, Fast (SPIF) Small Computer Systems Interface (SCSI).
SCSI/Processor Interconnect, Fast (SPIF)
An enhanced version of the SCSI/Processor Interconnect the SPIF is used in systems based on the Highly Scalable bus.) See also SCSI/Processor Interconnect (SPI), Small Computer Systems Interface (SCSI).
SCSI-V board
In older Symmetry systems: A VMEbus board that provides an S16 or S2000/2x0 system with two additional SCSI buses for disk drives.
SDH
See Synchronous Digital Hierarchy (SDH).
SDLC
See synchronous data link control (SDLC).
SEAL
See simple and efficient AAL (SEAL).
search path
A list of directories searched by the shell when a command pathname is not specified. See also pathname.
SEC
See SCSI Expansion Cabinet
secondary half-session
In SNA networking: The half-session that receives the session-activation request. See also primary half-session.
secondary logical unit (SLU)
In SNA networking: The logical unit that receives the Bind Session (BIND) request for a particular logical unit-to-logical unit (LU-to-LU) session. See also logical unit (LU), primary logical unit (PLU).
security descriptor
In Windows NT: Security-related information associated with every object in the Windows NT operating system. The main feature of a security descriptor is a list of protections, called the access control list (ACL), that apply to the object.
security identifier (SID)
In Windows NT: A string that uniquely identifies the user to the NT operating system's security functions. Usually corresponding to the user's login name, it may also incorporate the name of a group to which the user belongs. The SID is one of the components of an access token. See also access token.
segmentation and reassembly (SAR)
In OSI networking: One of the two sublayers of the Asynchronous Tranfer Mode (ATM) Adaptation Layer (AAL) common part convergence sublayer (CPCS) responsible for dividing (at the source) and reassembling (at the destination) the protocol data units (PDUs) passed from the convergence sublayer (CS). The SAR sublayer takes the PDUs processed by the CS and, after dividing them into 48-byte pieces of user data, passes them to the ATM layer for further processing. See also Asynchronous Tranfer Mode (ATM), ATM Adaptation Layer (AAL), common part convergence sublayer (CPCS), convergence sublayer (CS), protocol data unit (PDU).
select window
In ptx/ADMIN: A window that allows the user to select one or more items for entry into a field.
selector
In OSI networking: The portion of an address that identifies a particular entity at that address; for example, a session selector identifies a user of the session service residing at a particular address.
semaphore
In programming: A shared data structure used to synchronize the actions of multiple cooperating processes.
semopset
In programming: A collection of semaphore-controlled operations that work as one operation. If some event prevents completion of the semopset, any operations that have been performed are undone.
Sendmail
In UNIX-based operating systems: A program that controls mail routing and address parsing.
sequential execution
  1. The execution of multiple commands typed on the same line. The commands, separated by semicolons, execute in the order in which they appear on the line.
  2. The processing of computer instructions one after another; as opposed to parallel execution. See also parallel execution.
server
The program satisfying the request in a system in which a program at one site sends a request to a program at another site. See also host(2), display server.
service access point (SAP)
In OSI networking: The point at which a communications protocol layer receives services from the underlying layer.
service data unit (SDU)
In OSI networking: A unit of information from an upper-layer protocol that defines a service request to a lower-layer protocol.
service interface
In network programming for UNIX-based systems: A specified set of messages and the rules for allowable sequences of messages across the boundary of neighboring components within a stream.
service procedure
In network programming for UNIX-based systems: The queue routine that receives a message from the queue's message list, processes it, and passes it to the following queue's put procedure. The STREAMS scheduler calls the service procedure.
service provider
In a service interface: The entity (typically a module or driver) that responds to request primitives from the service user with response and event primitives.
service user
In networking: The entity that generates request primitives for the service provider and consumes response and event primitives.
session
In SNA networking: A logical or virtual path established between two network addressable units (NAUs) for the purpose of exchanging data. See also network addressable unit (NAU).
session layer
In OSI networking: The layer that adds control mechanisms to the data exchange; often called ''layer 5.'' See also Open System Interconnection (OSI) reference model.
session limit
In SNA networking: The flow-control technique that permits a receiving session to control the data transfer rate (the rate at which it receives request units) on the normal flow. It is used to prevent overloading a receiver with unprocessed requests when the sender can generate requests faster than the receiver can process them. See also pacing.
session partner
In SNA networking: One of the two network addressable units (NAUs) engaged in an active session. See also network addressable unit (NAU).
session presentation services
In SNA networking: The component of the FMD services layer that provides, within a logical unit-to-logical unit (LU-to-LU) session, services (such as formatting data for display or printing) to the application programmer or terminal operator. See also logical unit (LU).
session services
In SNA networking: One of the types of network services in the system services control point (SSCP) and in a logical unit (LU). These services provide facilities for a logical unit (LU) or network operator to request that the SSCP initiate or terminate sessions between logical units. See also logical unit (LU), system services control point (SSCP).
session services access point (SSAP)
Under Construction.
set-associative cache
A cache-memory architecture that divides the cache memory into banks or "ways" the same size as a memory page.
shared-memory multiprocessor
A type of computer system in which all processors share a single memory system. The processors in such a system are able to cooperate with one another and balance the workload among themselves by passing data back and forth through the shared memory system. This type of design is called "tightly-coupled."
shell
A program responsible for handling all interaction between the user and the operating system. Shells include a limited programming language with which shell scripts can be written. See also shell script.
shell script
A file containing commands that can be interpreted by the shell. The user types the name of the script file at the shell command prompt to make the shell execute the script commands.
shut down
To halt or stop a computer system.
SIC
See Scan Interface Controller (SIC).
SID
See security identifier (SID).

SilkWorm

"SilkWorm" refers to the first generation 16-port Fibre Channel Switch. "SilkWorm Express" refers to the first generation 6-port switch. (our special model is 6-port; Brocade's standard model is 8-port.) "SilkWorm 2800" is the term for the second generation 16-port switch. "SilkWorm 2400" is the name for the second generation 8-port switch.

The "SilkWorm 2000 family of switches" or the "SilkWorm 2000 family" are terms that refer to the newer switch models (SilkWorm 2800 and SilkWorm 2400). "SilkWorm 1000 family" refers to the older generation of switches, which included the 16-portSilkWorm and the 6-port SilkWorm Express (see above).

simple and efficient AAL (SEAL)
In OSI networking: A scheme used by ATM Adaptation Layer 5 (AAL5), in which the segmentation and reassembly (SAR) sublayer segments convergence sublayer (CS) protocol data units (PDUs) without adding additional fields. See also ATM Adaptation Layer (AAL), convergence sublayer (CS), protocol data unit (PDU), segmentation and reassembly (SAR).
simple disk
An unpartitioned ptx/SVM disk that contains a small area for private configuration database and header information, and a large public area that ptx/SVM uses for subdisk storage.
Simple Mail-Transfer Protocol (SMTP)
An Internet protocol providing electronic mail services.
Simple Network-Management Protocol (SNMP)
In computer networking: A protocol used to monitor IP gateways and the networks to which a gateway is attached. SNMP defines a set of variables to be stored on each gateway in the Management Information Base (MIB) database. An SNMP agent on the gateway keeps track of variables and responds to SNMP requests. An SNMP manager resides on a system on the network and sends out requests for network information from SNMP agents. The information returned by the agents is processed by the manager and displayed on the manager's system. See also Management Information Base.
single inline memory module (SIMM)
In computer hardware: A small circuit card that carries a number of surface-mounted memory chips in a space-saving configuration with the connector pins protruding in a single line from the edge of the card. Varying numbers of SIMMs can be plugged easily into slots in a memory board to expand random-access memory.
single-mode fiber
A type of optical fiber, typically used with Gigabaud Link Modules (GLMs) incorporating longwave lasers. Typically used for long-distance links up to 10 km. See also Gigabaud Link Module (GLM).
single-mode optical transmission
In fiber-optical transmission: The propagation of light on a single path through an optical fiber of small core diameter. The single path allows transmissions up to 10 km.
single-user mode
In UNIX-based operating systems: A state of the computer that allows only the superuser to gain access to the operating system.
site
A place where one or more computer systems are installed. To operate properly over their intended service life, computer systems typically require certain site conditions, such as a stable electrical power supply and adequate circulation of clean, cool air around the system.
site license
Authorization to use a software product on all computers at a site.
slave system
In UNIX networking: A system that receives a UNIX-to-UNIX copy (UUCP) call. See also UNIX-to-UNIX copy (UUCP).
SLIC
See System-Level Interrupt Controller (SLIC).
SLIC bus
See System-Level Interrupt Controller (SLIC) bus.
slice
See partition.
sliced disk
A ptx/SVM disk that consists of one type-8 partition designated to contain the configuration database and one non-type-3, type-8, or type-9 partition for data.
SLU
See secondary logical unit (SLU).
Small Computer Systems Interface (SCSI)
A family of hardware interfaces based on the ANSI X3.131-1986 standard which are used to connect peripherals such as disk and tape drives to computer systems. Derivatives of the original single-ended narrow SCSI bus (SCSI-1) include Differential SCSI, Wide Differential SCSI, and Fast Wide Differential SCSI.
SMD-E
See Storage Module Disk - Extended (SMD-E).
SMT
See surface-mount technology (SMT).
SMTP
See Simple Mail-Transfer Protocol (SMTP).
SNA character string (SCS)
See Systems Network Architecture (SNA) character string (SCS).
SNA network
A data communications network employing IBM's Systems Network Architecture. See Systems Network Architecture (SNA).
SNDCF
See Subnetwork-Dependent Convergence Facility (SNDCF).
SNMP
See Simple Network-Management Protocol (SNMP) .
snode
The filesystem-specific node that underlies Virtual File System (VFS) vnodes for device-special files, FIFO files, and pipe files. See also Virtual File System (VFS), vnode.
SNPA
See subnetwork point of attachment (SNPA).
socket
In TCP/IP networking: A software interface that gives an application program access to the TCP/IP services. An alternative to the Transport Layer Interface. See also Transport Layer Interface (TLI).
space files
Files that contain configurable source code for device drivers or that list system configuration parameters. These files are called space files because they specify the space requirements for the kernel. The total space requirements will affect the amount of memory used by the kernel.
spawn
To create a process; for example, at boot time, the init process spawns a getty process for each TTY port that can accept logins.
special character
A character that instructs the shell to perform a task such as redirecting input or output, or matching filenames on the command line.
special file
A file that represents a physical device such as a printer, terminal, or disk drive. When the system reads from and writes to these files, the read and write requests activate the device handler associated with the file.
SPI
See SCSI/Processor Interconnect (SPI).
SPIF
See SCSI/Processor Interconnect (SPI), Fast (SPIF).
split transaction
A concept used on the Symmetry System Bus (SSB) and Highly Scalable Bus (HSB), in which a read or write transaction on the bus need not take place during contiguous bus cycles. See also Symmetry System Bus (SSB), Highly Scalable Bus (HSB).
spool
In UNIX-based operating systems: To queue a job for completion in the background. Print requests and UUCP jobs are spooled.
SSAP
See session services access point (SSAP).
SSB
See Symmetry System Bus (SSB).
SSCP
See system services control point (SSCP).
SSCP services
In SNA networking: The components in a system services control point (SSCP) that provide configuration, maintenance, management, network, and session services for SSCP-to-LU, SSCP-to-PU, and SSCP-to-SSCP sessions. See also Logical Unit (LU), Physical Unit (PU), system services control point (SSCP).
SSCP-to-LU session
In SNA networking: A session between a system service control point (SSCP) and a logical unit (LU); the session enables the LU to request the SSCP to help initiate LU-to-LU sessions. See also Logical Unit (LU), Physical Unit (PU), system services control point (SSCP).
SSCP-to-PU Session
In SNA networking: A session between a system services control point (SSCP) and a physical unit (PU); SSCP-to-PU sessions allow SSCPs to send requests to, and receive status information from, individual nodes to control the network configuration. See also Physical Unit (PU), system services control point (SSCP).
SSCP-to-SSCP session
In SNA networking: A session between the system service control point (SSCP) in one domain and the SSCP in another domain. An SSCP-to-SSCP session is used to initiate and terminate cross-domain logical unit-to-logical unit (LU-to-LU) sessions. See also Logical Unit (LU), system services control point (SSCP).
SSM
See System Services Module (SSM).
SSM-2
See System Services Module - 2 (SSM-2).
stand-alone kernel
In IBM NUMA systems, a subset of the UNIX kernel that lives in the flash PROM of the Management and Diagnostics Controller (MDC). It includes only those modules necessary for a stand-alone environment and does not provide a swap device. The stand-alone kernel reads the boot strings from the MDC and loads the UNIX-kernel or stand-alone utility specified by the boot strings.
stand-alone program
In computer operating systems: A program that can be used when the operating system is not running.
star topology
In network architecture: A network topology in which every node on the network is connected to a central node or "hub," through which they communicate with each other.
station
In OSI network architecture: A uniquely addressed network device. Stations implement the services defined by the Data Link and Physical layers of the OSI reference model. See also Open Systems Interconnection (OSI) reference model.
statistical multiplexing
Technique whereby information from multiple logical channels can be transmitted across a single physical channel. Statistical multiplexing dynamically allocates bandwidth only to activate input channels. This makes better use of available bandwidth and allows more devices to be connected than with other multiplexing techniques.
STM-1
See Synchronous Transport Module level 1 (STM-1).
Storage Module Disk - Extended (SMD-E)
An industry-standard disk-drive interface.
stream
In the DYNIX/ptx operating system: A full-duplex processing and data-transfer path between a STREAMS driver in kernel space and a process in user space. A stream is created using the STREAMS mechanism. The primary components of a stream are the stream head, the driver, and zero or more modules between the stream head and driver. See also STREAMS.
stream end

In the DYNIX/ptx operating system: The module farthest from the user process, in which the processing procedures are driver routines. A stream-end's procedures are different from those in other modules because they are accessible from an external device and because the STREAMS mechanism allows multiple streams to be connected to the same driver (the same stream end).

The terms stream end and driver are often used interchangeably.

stream entity
In the DYNIX/ptx operating system: Any one of the elements of which a stream is made: a driver, module, multiplexor, or stream head.
stream head
In the DYNIX/ptx operating system:The end of the stream closest to the user process. The stream head provides the interface between the stream and the user process. Its principal functions are processing of STREAMS-related system calls and bidirectional transfer of data between a user process and messages in the STREAMS kernel space.
STREAMS
In the DYNIX/ptx operating system: The set of utility routines, kernel facilities, and structures that define interface standards for character input and output.
string
A series of characters.
string control byte (SCB)
In SNA networking: An optional control byte in the SCS data stream that identifies how end-user data is compressed or compacted. See also compaction, compression.
striping
In ptx/SVM: A type of plex layout where data blocks are interleaved between subdisks. Data is written alternately to a portion, or stripe, of each subdisk on multiple disks.
STS-1
See Synchronous Transport Signal level 1 (STS-1).
subarea
The combination of a host or communication controller and its attached peripheral nodes.
subdirectory
In computer operating systems: A directory located "below" another directory in the filesystem. Also called a child directory.
subdisk
In ptx/SVM: The smallest logical building block of ptx/SVM. A subdisk is mapped directly to part or all of a single physical disk partition. Subdisks make up plexes, which make up ptx/SVM volumes. See also plex, volume.
submenu
In computer user interfaces: A menu that appears as an option on another menu.
subnet addressing
See subnetting.
subnet mask
See netmask.
subnetting
The "Internet Standard Subnetting Procedure" is specified in RFC 950. Also known as "subnet addressing," subnetting is a widely used technique that allows a single network address to be divided into multiple logical networks, each of which forms a subset of the total network address space. Subnetting is now a required extension of the IP addressing scheme.

The advantage of subnetting is that it allows partitioning of the network address space within an organization without affecting the way senders outside the organization address messages sent to it. The internal organization is wholely contained within the organization.
See also netmask.

subnetwork
A logical subsection of a network. Sometimes called ''subnet.'' See also subnetting.
Subnetwork-Dependent Convergence Facility (SNDCF)
Under Construction.. (ISO 8473 and 9068).
subnetwork point of attachment (SNPA)
Under Construction.
suffix
See filename extension.
superblock
In UNIX-based operating systems: A block containing critical information about the filesystem, such as the filesystem type, layout, and size. The ptx/EFS superblock is located 1024 bytes from the beginning of the filesystem and is 1024 B long.
superuser
In UNIX-based operating systems: Owner of most system files and user of the root login name. The superuser has access to every file, regardless of its permission levels. Most system administration tasks are performed by the superuser under the root login name.
surface-mount technology (SMT)
A method for manufacturing printed circuit boards in which chips are fixed directly to the surface of the board instead of being soldered into predrilled holes.
SVC
See switched virtual circuit (SVC).
SVID
See System V Interface Definition (SVID).
SVR4
UNIX System V Release 4.
svsema
See System V semaphore (svsema).
swap device
A reserved set of disk partitions that store processes temporarily. When there is not enough primary memory to contain all the processes that are running, the kernel writes processes to a swap device. Later, the kernel reads the data from the swap device back into primary memory.
swap partition
See swap space.
swap space
Disk space reserved to hold processes that are swapped out of primary memory.
switched line
A telecommunication line in which the connection is established by dialing. See also dedicated line.
Switched Multimegabit Data Service (SMDS)
Wide-area network technology featuring high-speed packet switching of datagrams.
switched virtual circuit (SVC)
In data-communications networking: A virtual circuit that is dynamically established on demand and is torn down when transmission is complete. SVCs are used in situations where data transmission is sporadic. In Asynchronous Tranfer Mode (ATM) networking: "switched virtuial connection." Compare with permanent virtual circuit (PVC). See also Asynchronous Tranfer Mode (ATM).
symbolic address
In UNIX-based operating systems: A character representing a specific line in a text file. Used by the ed and vi editors.
symmetric multiprocessing
A system in which all CPUs are identical, and any CPU can execute both user code and kernel code. In the Symmetry system architecture, all CPUs operate on a peer basis, executing a single copy of the operating system executive or kernel. There is no designated master CPU except during system start-up and diagnostic operations. Any process (program) in any state can execute on any CPU.
Symmetry 2000 systems
A family of computers, now obsolete, built around the Symmetry System Bus (SSB) architecture. See also Symmetry System Bus (SSB).
Symmetry 5000 systems
The family of computers running the DYNIX/ptx operating system and using the Highly Scalable Bus (HSB). A collective term for the SE20, SE30, SE40, SE60, SE70, and SE80 computer systems. See also Highly Scalable Bus (HSB).
Symmetry System Bus (SSB)
A 64-bit bus that links the S2000 systems' CPUs, memory, and I/O subsystems. Peripheral interface boards connected to the SSB allow the CPUs to access mass-storage devices, printers, and other peripherals that are connected to the Small Computer Systems Interface (SCSI) bus and the VMEbus or MULTIBUS. 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. See also MULTIBUS, Small Computer Systems Interface (SCSI), VMEbus.
synchronous
Pertaining to two or more processes that depend upon the occurrence of specific events, such as common timing signals.
Synchronous Communications Controller (SCC)
A MULTIBUS board providing four high-speed RS-232-C serial interface ports to support the High-Level Data Link Control (HDLC) data-link protocol for use in X.25 networks. See also High-Level Data Link Control (HDLC), MULTIBUS.
Synchronous Communications Controller - VMEbus (SCC-V)
A VMEbus board providing two RS-232-C and two RS-442/449 high-speed serial interface ports to support the High-Level Data Link Control (HDLC) data-link protocol for use in X.25 networks. See also High-Level Data Link Control (HDLC), VMEbus.
synchronous data link control (SDLC)
  1. A discipline for managing synchronous, code-transparent, serial-by-bit information transfer over a link connection. Transmission exchanges may be duplex or half-duplex over switched or nonswitched links. The configuration of the link connection may be point-to-point, multipoint, or loop.
  2. In SNA networking: The primary data link control protocol. SDLC transfers data and control and status information.
Synchronous Digital Hierarchy (SDH)
European standard that defines a set of rate and format standards transmitted using optical signals over fiber. STS-1 is similar to Synchronous Optical Network (SONET) with a basic SDH rate of 155.52 Mbps, designated at STM-1. See also Synchronous Transport Module level 1 (STM-1), Synchronous Optical Network (SONET).
Synchronous Optical Network (SONET)
In OSI networking: High-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. Approved as an international standard.
Synchronous Transport Module level 1 (STM-1)
One of a number of SDH formats that specifies that frame structure for the 155.52-Mbps lines used to carry Asynchronous Tranfer Mode (ATM) cells. See also Asynchronous Tranfer Mode (ATM), Synchronous Digital Hierarchy (SDH).
Synchronous Transport Signal level 1 (STS-1)
In OSI networking: Basic building block signal of Synchronous Optical Network (SONET), operating at 51.84 Mbps. Faster SONET rates are defined as STS-n, where n is a multiple of 51.84 Mbps. See also Synchronous Optical Network (SONET).
synchronous write
A form of synchronous I/O that writes the file data to disk, updates the inode times, and writes the updated inode to disk. When the write returns to the caller, both the data and the inode have been written to disk.
syntax
  1. In programming: The rules governing the structure and content of the statements in a computer language.
  2. In computer operating systems: The content and structure of the character strings which, entered at the command line, instruct the operating system to run a program.
system
In IBM NUMA computers: A single or a cluster of nodes acting as a single computing entity. A system in this sense may run multiple instances of the operating system. See also cluster, node.
System V Interface Definition (SVID)
In UNIX-based operating systems: An AT&T specification for the UNIX System V operating system. SVID Release 3 (SVID-III) specifies the interface for UNIX System V Release 4.
System V semaphore (svsema)
In UNIX-based operating systems: A flag for controlling access to shared memory.
system administrator (SA)
A person responsible for the overall operation of the computer system. The SA's duties include adding and removing user names and devices, performing configuration tasks, and monitoring system activity.
system configuration file
A text file that specifies the modules and device configurations to be included in the kernel. The default system configuration file is /etc/conf/uts/symmetry/system.std. This file serves as input to the config program.
system default destination printer
A printer or class that receives print requests that do not include a destination. If a user has not set the LPDEST variable and does not specify a destination for a print request on the command line, the print request goes to the system default destination.
system directory
In UNIX-based operating systems: A directory containing files used by the operating system. Examples include /dev (containing device nodes), /etc (containing system administration files), and /usr and /bin (containing programs).
System-Level Interrupt Controller (SLIC)
An integrated circuit used to generate and process the signals which coordinate activity on the Symmetry system bus. Each board connected to the Symmetry system bus has a SLIC chip. See also System-Level Interrupt Controller (SLIC) bus.
System-Level Interrupt Controller (SLIC) bus
A 1-bit data path in the system backplane that interconnects all the SLICs in the system. The various subsystems and CPUs in a Symmetry system use the SLIC bus to exchange interrupts and other low-level control signals, configuration information, and error information.
system name
The name for a system. In a network, this name is typically the same as the node name.
system services control point (SSCP)
In SNA networking:
  1. A special-purpose network addressable unit (NAU) that controls and manages resources in a network domain. The SSCP initiates or establishes communication within the network. See also network addressable unit (NAU).
  2. A focal point for managing the configuration, coordinating network-operator and problem-determination requests, and providing directory support and other session services for end users of the network. Multiple SSCPs, cooperating as peers, can divide the network into domains of control, with each SSCP controlling the physical and logical units in its domain. See also Systems Network Architecture (SNA) network, SSCP services.
System Services Module (SSM)
A circuit board used in the S16 and Symmetry 2000/200 systems. The SSM provides these systems with initialization, system-bus services, power-supply monitoring, and an interface with the front panel. The SSM includes a differential Small Computer Systems Interface (SCSI) bus, a VMEbus interface, two serial ports, and a parallel printer port. See also Small Computer Systems Interface (SCSI), VMEbus.
System Services Module - 2 (SSM-2)
A circuit board used in the Symmetry 2000/4x0 and Symmetry 2000/7x0 systems. The SSM-2 provides these systems with initialization, system-bus services, power-supply monitoring, and an interface with the front panel. The SSM-2 includes a differential Small Computer Systems Interface (SCSI) bus and two serial ports. See also Small Computer Systems Interface (SCSI), System-Level Interrupt Controller (SLIC) bus.
System Services Section
A functionally distinct portion of the CSM board; it provides Symmetry 5000 and WinServer 5000 systems with initialization, system-bus services, power-supply monitoring, and an interface with the front panel. See also High-Performance SCSI and Ethernet (HPSE).
Systems Network Architecture (SNA)
  1. IBM's communications architecture, which permits distributed processing in a mainframe environment.
  2. Description of the logical structure, formats, protocols, and operational sequences for transmitting information units through and controlling the configuration and operation of networks.
Systems Network Architecture (SNA) character string (SCS)
In SNA networking: A string of EBCDIC control characters carried within a request/response unit (RU); the string may also contain end-user data. See also request/response unit (RU), EBCDIC.
Systems Network Architecture (SNA) functional layers
The division of network services into five layers, as defined in IBM's Systems Network Architecture. From top to bottom the layers are Function Management, Data Flow Control, Transmission Control, Path Control, and Data Link Control. SNA predated the Open Systems Interconnection (OSI) standard's seven-layer model.
Systems Network Architecture (SNA) network
A data communications network employing IBM's Systems Network Architecture. See Systems Network Architecture (SNA).


T

T3
In OSI networking: Digital wide-are network (WAN) carrier facility. T3 transmits DS-3-formatted data at 44.736 Mbps through the telephone switching network. Compare with E3.
tape
A serial magnetic medium on which data is stored.
target
In ptx/LICENSE: The node on which a password is to be installed. If the password specifies a single nodelocked license, the target is the node licensed to run the product. If the password specifies multiple nodelocked licenses (that is, a compound password for nodelocked licenses), or licenses of any other type, then the target is a node running the license management daemon.
target ID
In ptx/LICENSE: The identifier of the node (in IBM NUMA-Q 2000 systems) or system (in Symmetry systems) on which a password is to be installed.
Target System Control Library (TSCL)
The low-level command layer between system hardware and Virtual Control Software (VCS). See also Virtual Control Software (VCS).
TCAM
See telecommunications access method (TCAM).
TCP
See Transmission Control Protocol (TCP).
TCP/IP
See Transmission Control Protocol (TCP), Internet Protocol (IP).
TDM
See time-division multiplexing (TDM).
Technical Office Protocol (TOP )
In OSI network architecture: An architecture developed by Boeing for office communication. See also Open Systems Interconnection (OSI) reference model.
Telebit
A brand of modem.
telecommunications access method (TCAM)
A service used by an application program to move data to and from an I/O device.
teletypewriter (TTY)
Originally an electromagnetic device consisting of a combined keyboard and printer, used to communicate over telephone lines or other wired serial connections using the ASCII code. The abbreviation TTY is now used to describe any serial "teletypewriter-like" connection.
teletypewriter (TTY) line
An RS-232-C transmission line used for connecting serial devices such as terminals and printers. See also teletypewriter (TTY).
TELNET (TELecommunications NETwork)
In networking: A standard Internet protocol for terminal emulation.
termcap (TERMinal CAPability) file
Terminal capability database defining a given type of terminal, such as VT100, network, hp, dialup, and so forth; contains details about each type of terminal, such as lines-per-screen, columns-per-line, and cursor-control codes. The word termcap is also used in reference to a line in the file.
Terminal Line Controller - Multibus (TLC-M)
A set of two MULTIBUS boards that provides 16 serial ports for connecting terminals, modems, and other serially interfaced devices. See also MULTIBUS.
Terminal Line Controller - VMEbus (TLC-V)
A VMEbus board that provides 16 serial ports for connecting terminals, modems, and other serially interfaced devices. See also VMEbus.
TFTP
See Trivial File-Transfer Protocol (TFTP).
throughput
A measure of work accomplished in a given amount of time. For filesystems, throughput typically refers to the numbers of I/O operations performed in a given amount of time.
tightly coupled multiprocessor
See shared-memory multiprocessor.
time-division multiplexing (TDM)
Techniques in which information from multiple channels can be allocated bandwidth on a single wire based on preassigned time slots. Bandwidth is allocated to each channel regardless of whether the station has data to transmit.
time stamp
In ptx/LICENSE: An integer that describes the date and time at which a set of licenses was created.
time-sharing option (TSO)
An optional configuration of IBM's operating system providing conversational time-sharing from remote stations.
TLC-M
See Terminal Line Controller - Multibus (TLC-M).
TLC-V
See Terminal Line Controller - VMEbus (TLC-V).
TLI
See Transport-Layer Interface.
token
In networking: A string of bits that passes from one station to the next on a bus or ring. A station that wishes to transmit a message retrieves the token and places its message on the medium with the token behind it.
TOP
See Technical Office Protocol.
topology
In networking: The pattern described by the interconnections among the nodes in a network. Common topologies include ring, bus, and star.
Tpn
TP"n"
Transport Protocol, Class "n" (ISO 8073).
TPS
See transactions per second (TPS).
trace
A record of the execution of a computer program. A trace records the sequence in which the instructions were executed.
track
A portion of a disk platter that can contain data.
transaction
In UNIX-based operating systems: An update to the filesystem structure.
transaction program
In TCP/IP networking: An application program executed in response to a transaction request. See also Transmission Control Protocol (TCP).
Transaction Services Layer
In SNA networking: The functional layer that establishes a logical interface for the end user.
transactions per second (TPS)
A rating of the performance of a computer system, based on the average number of transactions the system can perform in one second.
Transmission Control Layer
In SNA networking: The functional layer that provides services controlling the rate and sequence of data transmission.
Transmission Control Protocol (TCP)
Transmission Control Protocol (TCP) establishes a full-duplex and reliable communication connection between two hosts. TCP receives outgoing messages from higher layers and adds information to ensure that the message arrives at the correct peer on the destination host. TCP also directs incoming messages to the correct higher layer entity. TCP is most commonly used with the Internet Protocol (IP) for a wide variety of data communications, including the Internet. See also Internet, Internet Protocol (IP).
Transmission Control Protocol/Internet Protocol (TCP/IP)
A widely used networking protocol first developed for the Department of Defense. It combines the Transmission Control Protocol (TCP) and the Internet Protocol (IP). See also Transmission Control Protocol (TCP), Internet Protocol (IP).
transmission header (TH)
In SNA networking: Control information in Layer 4 of the SNA networking protocol that is created and used by path control to route message units and to control their flow within the network.
transmitter
An electronic circuit that converts an electrical logical signal to a signal suitable for the communications medium (optical or electrical). In the Fiber Channel Bridge, a laser diode in the Gigabaud Link Module (GLM) component assembly. See also bridge: In Fibre Channel,Gigabaud Link Module (GLM).
transparent data
Data in a transmit data set that is not interpreted as containing control characters. Transparent data is preceded by a control byte and a count of the number of bytes of data that follow.
Transport Layer
In OSI network architecture: The layer responsible for providing services to bridge the gap between the network layer and the session layer. Transport functions deal with service quality and cost optimization (such as error control, flow control, sequencing, and multiplexing). The transport layer is often referred to as layer 4. See also Open Systems Interconnection (OSI) reference model.
Transport-Layer Interface (TLI)
In TCP/IP networking: An alternative means by which an application program gains access to the TCP/IP services. See also socket.
Transport Library Interface
A misinterpretation of TLI. Substitute "Transport-Layer Interface."
transport service access point (TSAP)
Under Construction..
Trivial File-Transfer Protocol (TFTP)
In TCP/IP networking: A standard TCP/IP protocol for transferring files between systems.
TSAP
See transport service access point (TSAP).
TSCL
See Target System Control Library (TSCL).
TSO
See time-sharing option (TSO).
TTY
See teletypewriter (TTY).
teletypewriter (TTY) line
An RS-232-C transmission line used for connecting serial devices such as terminals and printers.
tunable parameters
In UNIX-based operating systems: Values in the kernel that can be changed to affect system performance. Also called configurable parameters.
twisted-pair
A transmission medium in which two insulated wires are twisted together to reduce interference.


U

UDP
See User Datagram Protocol.
UDP
See User Datagram Protocol (UDP).
UFS
In the DYNIX/ptx-based operating system: A filesystem type derived from the V4.2 Berkeley Fast filesystem.
UID
See User ID (UID).
UKDI
See United Kingdom domain identifier (UKDI).
UKDP
See United Kingdom domain part (UKDP).
UKDSP
See United Kingdom domain-specific part (UKDSP).
UKFI
See United Kingdom format identifier (UKFI).
unattended operation
The automatic transmission and reception of messages without human intervention.
unbuffered I/O
I/O that bypasses the filesystem cache for the purpose of increasing I/O performance; also called "direct I/O."
unformatted
Describing a disk not yet ready to be used for storing data.
uninterruptible power supply (UPS)
A device connected between a computer and its power source that protects the computer against blackouts, brownouts, and power surges. The UPS contains a power sensor to monitor the supply and a battery to provide power until an orderly shutdown of the system can be performed.
uniprocessing
Computation by a system with a single central processing unit (CPU).
United Kingdom domain identifier (UKDI)
In OSI networking: Under Construction.
United Kingdom domain part (UKDP)
In OSI networking: Under Construction.
United Kingdom domain-specific part (UKDSP)
In OSI networking: Under Construction.
United Kingdom format identifier (UKFI)
In OSI networking: Under Construction.
UNIX-to-UNIX copy (UUCP)
In UNIX-based operating systems: a UNIX command that copies a source file to a destination file.
unmount
In UNIX-based operating systems: To make (a filesystem) inaccessible to users.
unnamed fileset
A fileset that contains files that are visible to and accessible by users.
upload
To transfer data from a small (typically local) computer to a large (typically remote) computer.
upper multiplexer
See multiplexer.
upper stream
A stream terminating above a multiplexer. The upstream end of an upper stream originates at the stream head or another multiplexer driver.
UPS
See uninterruptible power supply (UPS).
upstream
The direction from the driver towards the stream head.
USENET
A major UNIX-to-UNIX copy (UUCP) network of computers across the country having UUCP connections.
use-once license
In ptx/LICENSE: A type of license administered by the license server that can be used for a single instance of invoking a product or of using a service. The license server decrements the number of use-once licenses each time the product is used.
user account
In UNIX-based operating systems: An entry in the /etc/passwd file that defines a user's login name, ID, home directory, and default shell program. The user's password, which is stored in the /etc/shadow file, is also part of a user account.
User Datagram Protocol (UDP)
A connectionless and therefore unreliable means of transferring data between machines.
user file
In ptx/LICENSE: A text file that specifies users who are allowed or forbidden to use licensed software products.
user ID (UID)
In the UNIX operating system: A string that uniquely identifies each user to the operating system.
UUCP
See UNIX-to-UNIX copy (UUCP).
uugetty utility
In UNIX-based operating systems: A program similar to getty that allows a teletypewriter (TTY) line to be used for both logins and outgoing calls. This program allows a modem to accept incoming calls and make outgoing calls through the same port. See also teletypewriter (TTY) line.


V

variable
A named entity to which a value is assigned, either on a command line or in a file.
variable-length record
A record having a length independent of the length of other records with which it is logically or physically associated. See also record, fixed-length record .
variable bit rate (VBR)
A quality of service (QOS) class defined by the ATM Forum for Asynchronous Tranfer Mode (ATM) networks. VBR is subdivided into a real time (RT) class and non-real time (NRT ) class. VBR (RT) is used for connections in which there is a fixed timing relationship between samples. VBR (NRT) is used for connections in which there is no fixed timing relationship between samples, but that still need a guaranteed QOS. See also Asynchronous Tranfer Mode (ATM), quality of service (QOS).
Vbad
See VMEbus Adapter Board.
VBIF
See VMEbus Interface Board.
VBR
See variable bit rate (VBR).
VC
See virtual circuit (VC).
VCC
See virtual channel connection (VCC).
VCI
See virtual channel identifier (VCI).
VCL
See virtual channel link (VCL).
VCS
See Virtual Control Software (VCS).
VDT
See video display terminal (VDT).
vectored superuser privileges
In DYNIX/ptx, the ability to assign certain superuser privileges to a specific process ID, or to all processes invoked by a specific UID (user ID) or GID (group ID).
vendor password
In ptx/LICENSE: A string encoded with information about a vendor which, together with a vendor ID, establishes the vendor of a licensed product in a license database.
version identifier
In ptx/LICENSE: A string by which the license server distinguishes among different versions of a product.
very large-scale integration (VLSI)
Describing an integrated circuit incorporating 10,000 or more logic gates.
VEU
See VMEbus Expansion Unit.
VFS
See Virtual File System (VFS).
VGA Controller board
A highly-scalable bus board required in WinServer systems to provide an interface to the VGA monitor, keyboard, and mouse which make up the system's VGA console.
video display terminal (VDT)
The combination of a video monitor, a keyboard, and typically some graphically-oriented input device such as a mouse, acting together as the basic input/output component of a computer system.
virtual
Describing a facility or path that appears to exist but does not actually exist. For example, virtual memory is the use of disk-based storage to simulate a larger address space than actually exists in system RAM.
virtual channel connection (VCC)
A logical circuit, made up of virtual channel links (VCLs), that carries data between two end points in an Asynchronous Tranfer Mode (ATM) network. Also called "virtual circuit connection." See also Asynchronous Tranfer Mode (ATM), virtual channel link (VCL).
virtual channel identifier (VCI)
In OSI networking: A 16-bit field in the header on an Asynchronous Tranfer Mode (ATM) cell. The VCI, together with the virtual path identifier (VPI), is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. ATM switches use the VPI/VCI fields to identify the next network virtual channel link (VCL) that a cell needs to transit on its way to its final destination. See also Asynchronous Tranfer Mode (ATM), virtual channel link (VCL), virtual path identifier (VPI).
virtual channel link (VCL)
A connection between two Asynchronous Tranfer Mode (ATM) devices. A virtual channel connection (VCC) is made up of one or more VCLs. See also Asynchronous Tranfer Mode (ATM), virtual channel connection (VCC).
virtual circuit (VC)
A logical circuit created to ensure reliable communication between two network devices. A virtual circuit is defined by a virtual path identifier (VPI)/virtual channel identifier (VCI) pair, and can be either a permanent virtual channel (PVC) or a switched virtual circuit (SVC). In Asynchronous Tranfer Mode (ATM), virtual circuit is called "virtual channel." See also Asynchronous Transfer Mode (ATM), switched virtual circuit (SVC), virtual channel identifier (VCI), virtual path identifier (VPI).
Virtual Control Software (VCS)
A collection of system management services, accessible through a GUI or remote interface, that allow a IBM NUMA system to be configured, booted, controlled, and diagnosed.
Virtual File System (VFS)
A filesystem abstraction layer defined by an Open Systems Interconnection (OSI) standard. VFS provides a uniform interface with any file on a network, regardless of the filesystem in which it actually resides.
virtual machine (VM)
Software that performs like a hardware device; for example, a program that allows applications written for an Intel processor to run on a Motorola chip.
virtual path identifier (VPI)
An 8-bit field in the header of an Asynchronous Tranfer Mode (ATM) cell. The VPI, together with the virtual channel identifier (VCI), is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. ATM switches use the VPI/VCI fields to identify the next virtual channel link (VCL) a cell needs to transit on its way to its final destination. See also Asynchronous Tranfer Mode (ATM), virtual channel identifier (VCI), virtual channel link (VCL).
Virtual Storage, Extended (VSE)
A multiuser, multitasking operating system developed by IBM.
Virtual Telecommunications Access Method (VTAM)
In SNA networking: A set of programs, designed by IBM, to control communication between end-user devices and application programs running under DOS/VS, VSE, OS/VS1, and OS/VS2.
virtual terminal (VT)
In networking: A process by which a network allows a variety of data terminals with different protocols and formats to communicate with each other. Each terminal's data is converted into a network standard format and then converted into the format of the receiving device at the destination end.
VLSI
See very large-scale integration (VLSI).
VM
See virtual machine (VM).
VMEbus
An asynchronous parallel communications bus designed to support high-speed communications among processor boards, memory boards, and peripheral I/O controller boards. It is also known as ''IEC 821 BUS'' and ''IEEE P1014/D1.2.''
VMEbus Adapter Board (VBAD)
A Highly Scalable Bus (HSB) board that provides the connection between the Highly Scalable Bus and the VMEbus Interface (VBIF) board in a VMEbus Expansion Unit (VEU). See also Highly Scalable Bus (HSB), VMEbus,VMEbus Expansion Unit (VEU), VMEbus Interface (VBIF) board.
VMEbus Expansion Unit (VEU)
The VMEbus card cage and interface boards used in S2000/4x0 and S2000 7x0 systems. See also VMEbus.
VMEbus Interface (VBIF) board
A board that provides an interface between the VMEbus and the NUMA system bus. See also VMEbus.
VMS Record Management System (RMS)
Under Construction..
vnode
Under Construction. See also snode.
volume
  1. In data storage hardware: A removable physical unit of any storage medium; for example, a tape reel or cartridge, a diskette, or a disk pack.
  2. In ptx/SVM: The logical equivalent of a single hard disk The logical components of a ptx/SVM volume, called plexes, are typically distributed over several different physical disks for the sake of performance or data protection. See also plex.
volume table of contents (VTOC)
In the DYNIX/ptx operating system: A partitioning driver. A VTOC file contains disk geometry information and defines the sizes and starting points of partitions on a disk.
volume table of contents, nonstandard (VTOC, nonstandard)
See nonstandard Volume Table of Contents (VTOC).
volume usage type
Designates how ptx/SVM determines which plex in a volume contains the most complete, up-to-date information after a system crash.
VPI
See virtual path identifier (VPI).
VSE
See Virtual Storage, Extended (VSE).
VT
See virtual terminal (VT).
VT100
A popular character-based video terminal developed by Digital Equipment Corporation. Many later terminals offered the capability of operating in VT100 emulation for network operations such as remote logins.
VTAM
See Virtual Telecommunications Access Method (VTAM).
VTOC
See volume table of contents (VTOC).
VTOC, nonstandard (volume table of contents, nonstandard)
See nonstandard Volume Table of Contents.

W

WAN
See Wide-Area Network (WAN).
watermark
A processing limit value used in flow control. Each queue has a high watermark and a low watermark. The value of the high watermark indicates the greatest number of bytes acceptable on the queue's message list. When the number of bytes on the message list reaches the high watermark, the flow-control mechanism blocks the preceding queue from sending messages to the queue that has exceeded its high watermark. When the number of bytes is reduced to the low watermark through service-procedure processing, flow control unblocks the preceding queue.
WCS
See writable control store (WCS).
well-known address
An address available to a set of programs, applications, or other processes. In ptx/TransACTION, for example, tmboot uses the TUXCONFIG file to create a set of data structures in shared memory on the master node, at an address known to all ptx/TransACTION processes.
well-known port

In TCP/IP networking: A TCP/IP protocol port permanently assigned to a service. All well-known ports for common services are agreed upon by the Internet community. In ptx/TCP/IP, well-known ports are defined in the /etc/services file. Also called a ''reserved port.'' See also protocol port.

wide-area network (WAN)
A network in which widely separated computers are connected by telephone lines or other means. Examples include X.25, Internet, MILNET, and ARPANET. See also local-area network (LAN).
Wide Quad-Channel I/O Controller board
A four-channel, wide-differential SCSI-2 controller board which connects to the Symmetry System Bus (SSB) or Highly Scalable Bus (HSB). The QCIC-W board controls up to 12 disk drives residing in Pbays on each channel, for a total of 48 drives per board. A maximum of eight Quad-Channel I/O Controller (QCIC) Board subsystems may be installed in an SE60 or SE70 system. See also Highly Scalable Bus (HSB), Pbay, Quad-Channel I/O Controller (QCIC) Board, Small Computer Systems Interface (SCSI), Symmetry System Bus (SSB).
wide SCSI
An implementation of the Small Computer Systems Interface (SCSI) standard. Wide SCSI allows up to sixteen devices, including the initiator or bus controller, to be attached to the SCSI bus. See also Small Computer Systems Interface (SCSI).
wildcard
See metacharacter.
Win32
An application programming interface (API) for the 386 processor's 32-bit mode, fully supported in Windows NT. Many functions are also supported in Windows 3.1, and applications can be written to the Win32 subset (Win32s) to gain improved performance on a 386 or higher processor running Windows 3.1 or higher. Windows 3.1 translates the 32-bit calls in a Win32s application into its native 16-bit calls.
window manager
In ptx/XWM: A client application that is used to manipulate windows. The mwm window manager is provided with ptx/XWM.
WinServer 5000 systems
A collective term for the obsolete WS20, WS30, WS40, WS60, WS70, and WS80 computer systems, all of which run the Windows NT operating system supplied by Microsoft.
workaround
A suggested method by which a known problem can be avoided or circumvented.
workgroup cabinet
A short IBM NUMA cabinet. See also NUMA-Q.
working directory
The current directory.
workstation
A powerful, single-user microcomputer, usually with a high-resolution display. Workstations are often used in conjunction with networked applications in which programs run on the workstation using data that resides on a server, which is connected to the workstation by a network.
wraparound
See autowrap.
writable control store (WCS)
Under Construction.
writeback
In ptx/SVM: A volume-level feature that manages read errors.
writecopy
In ptx/SVM: A volume-level feature that goes into effect when block-change logging is also enabled. Writecopy ensures the integrity of mirrored plexes by preventing certain forms of data corruption, but can entail a significant performance penalty.
write permission
In UNIX-based operating systems: On a directory, the capability to modify contents (as with the cp and rm commands). On a file, the capability to modify contents (as with the ed or vi editor). See also read permission.
write queue
In a module or driver, the queue containing messages moving downstream. The write queue is associated with a write(2) system call and output from a user process.
write-through cache
A cache system in which all data writes are sent directly to system memory, causing all caches with copies of that data to become invalid. Extra time is required for the invalidated caches to be refilled with valid data. Symmetry systems do not use write-through caching. See also copyback cache.

X

X
See X Window System.
X defaults
See resource.
XDR
See External Data Representation
X/Open Portability Guide (XPG)
A set of standards that specify compliance with X/Open's Common Application Environment (CAE); for example, XPG3 (Release 3), introduced in 1989, specifies standards for UNIX System V Release 4.0.
XPG
See X/Open Portability Guide (XPG).
X resources
See resource.
X Window System
A network-based graphics windowing system developed by MIT. X provides the foundation windowing system on which a graphical user interface (GUI) can be built. OSF/Motif, for example, is a user interface built on X.
X.25
The international protocol that defines how devices are connected to a packet-switched network. These devices are typically larger computers, mainframes, minicomputers, etc. Word processors, personal computers, workstations, dumb terminals, and the like do not support the X.25 packet switching protocols unless they are connected to the networkvia Packet Assembler/Disassemblers (PADs). See also Packet Assembler/Disassembler (PAD).