[ Previous | Next Page | Table of Contents | Library Home | Legal | Search ]



V. Volt.

V.24. The 24th CCITT recommendation in the V series, listing the definitions for interchange circuits between a DTE and a DCE.

V.35. The 35th CCITT recommendation in the V series, defining data transmission at 48 kilobits per second using 60-180 kHz group band circuits.

v-node. Virtual i-node. An object in a file system that represents a file. Unlike an i-node, there is no one-to-one correspondence between a v-node and the file system; multiple v-nodes can refer to a single file (a single i-node). V-nodes are used to communicate between the upper half of the file system (the logical file system) and the file system implementations (such as the journaled file system, the network file system, and the CD-ROM file system).

valid. (1.) Allowed. (2.) True, or conforming to an appropriate standard or authority.

validation. In X.25 communications, the process by which the receiving DTE accepts the packet size, packet window size, and throughput class sent by the sending DTE, on the conditions that they are valid. Contrast with negotiation.

valuator. (1.) An input device that provides a scale value; for example, a thumb wheel or a potentiometer. (2.) In GL, an input/output device that returns a value in a range. For example, a mouse is logically two valuators: the x position and the y position. See also dial.

value. (1.) A set of characters or a quantity associated with a parameter or name. (2.) In programming, the contents of a variable or a storage location. (3.) A specific occurrence of an attribute, such as blue for the attribute color. (4.) A quantity assigned to a constant, variable, parameter, or symbol. (5.) In XOM, an arbitrarily complex information item that can be viewed as a characteristic or property of an object. See also attribute value.

value logging. In the SOM Replication Framework, a technique for maintaining consistency among replicas of a replicated object, whereby the new value of the object is distributed after the execution of a method that updates the object.

variable. (1.) A name used to represent a data item whose value can change while the program is running. Contrast with constant. (2.) In programming languages, a language object that can take different values at different times. (3.) A quantity that can assume any of a given set of values. (4.) For Ada programming, see object.

variable length field. A field of varying length that contains data prefaced by an internal, opaque field providing the length of the field.

variable substitution. The ability to change and display the values of variables in a string, replacing a name of a variable with the value it represents.

variant part. In Pascal, the part of a record that can vary from one instance of the record to another. The variant part consists of alternate sequences of fields that share the same physical storage. In Ada language, a variant part of a record specifies alternative record components, depending on a discriminant of the record. Each value of the discriminant establishes a particular alternative of the variant part. See also tag field.

VC. See virtual circuit.

vchar. In ODM, a terminal descriptor type used to define a variable as a variable-length, null-terminated string. See also terminal descriptor.

VCI. Virtual channel identifier in an ATM network.

VDD. See virtual device driver.

vector. (1.) An array of one dimension. (2.) A quantity usually characterized by an ordered set of numbers. (3.) In computer graphics, a directed line segment.

vector graphics. (1.) Graphics for which the display images are generated from coordinates, as opposed to an array of pixels. (2.) The most common class of graphics, where all vector output consists of lines and curves drawn point-to-point by the output unit as ordered by the computer.

vector product. Another term for the vector cross product. If a = (a1, a2, a3) and b = (b1, b2, b3) are two three-dimensional vectors, the vector product a times b = (a2b3-b2a3, a3b1-b3a1, a1b2-b1a2).

vendor ID. In License Use Management, the identifier of a vendor of licensed products. By means of vendor IDs, license servers can distinguish among any number of vendors established in a network. Vendor IDs are an License Use Management-specific usage of Network Computing System Universal Unique Identifiers (UUIDs).

vendor password. In License Use Management, a string encoded with information about a vendor that, together with a vendor ID, establishes the vendor of a licensed product in a license database.

verify. (1.) To confirm the correctness. (2.) To determine whether a transcription of data or other operation has been accomplished accurately. (3.) In software installation, the verify procedure instructs the system to verify the software you are installing. The system confirms that your software files are the correct length and contain the correct number of digits and characters. If any errors are reported, it might be necessary to install the software product again. The verification process can add a significant amount of time to the installation process.

Versatile Message Transfer Protocol (VMTP). A protocol that provides datagram communication service at the user level. Unlike most programs that use UDP/IP, programs using VMTP do not have to implement time out, retransmission, or estimation of network delays because the VMTP protocol provides end-to-end datagram delivery.

version. A particular instance of an application program or licensed program. The version, release, modification, and fix levels of a program. The version, release, modification, and fix levels together comprise the program level or version of a program. A new version of a program usually has significant new code or functions compared to the previous version. See also fix number, program level, modification number, release number, and version number.

version control. The process by which the contents of each revision of software, hardware, or documentation are accounted for.

version identifier. In License Use Management, a string that identifies a version of a product; by means of version identifiers, the license server distinguishes among different versions of a product.

version number. The version level of a program, which is an indicator of the hardware and basic operating system upon which the program operates. The version, release, modification, and fix levels together comprise the program level or version of a program. See also fix number, modification number, release number, version and program level.

vertical retrace. (1.) The rate at which the monitor is refreshed. A 60 Hz monitor is redrawn 60 times per second. Synonymous with refresh rate. (2.) The action of moving the electron beam from the bottom to the top of the screen.

vertical retrace period. The amount of elapsed time between retraces of the screen. All video monitors use an electron beam to sweep the phosphors at the face of the monitor. Because the phosphors glow for only a brief period of time, the entire screen must be reswept periodically by the electron beam. On most monitors, this is done 30 times per second (30 Hz). Thus, the vertical retrace period is 1/30 second.

vhandle. An identifier for each object in VEOS. vhandles are used in graphics programming to identify software objects specified in VEOS. The vhandle can exist longer than the object that it identifies. After a software object such as a swidget is destroyed, the vhandle for that object remains defined.

video lookup table (VLT). A colormap implemented in hardware.

view-data paradigm. A SOM Replication Framework construct similar to the Model-View-Controller paradigm in SmallTalk. The "view" object contains only presentation-specific information, while the "data" object contains the state of the application. The "view" and "data" are connected by means of an "observation" protocol that lets the "view" be notified whenever the "data" changes.

viewable. Pertaining to a mapped window whose ancestors are all mapped; not necessarily visible. Graphics requests can be performed on a window when it is not viewable, but output will not be retained unless the server is maintaining backing store.

viewer coordinates. Synonym for eye coordinates.

viewing coordinates. Synonym for eye coordinates.

viewing matrix. In GL, a matrix used to describe the location of the viewer (the virtual eye looking upon a scene) in relation to the world. See also field of view, transformation, and world coordinates.

viewport. In GL, the mapping from normalized device coordinates to device coordinates. The viewport maps the unit cube x/w = +/-1, y/w = +/-1, z/w = +/-1 to the screen space, as measured in pixels. The viewport is the last transformation in the graphics pipeline. The viewport can be smaller or larger than the window and smaller or larger than the screenmask, although in most applications, it is the same size.

virtual address. The address of a location in virtual storage. A virtual address must be translated into a real address for the data or instruction it addresses to be accessible to the CPU.

virtual call facility . In data communications, a user facility in which a call-setup procedure and a call-clearing procedure determine a period of communication between two data terminal equipment (DTEs) in which user data is transferred in the network in the packet mode of operation. All user data is delivered from the network in the order it is received by the network. It is the packet network equivalent of a dialed line.

virtual circuit (VC). In X.25 communications, those facilities provided by a network that give the appearance to the user of an actual connection. See also switched virtual circuit and permanent virtual circuit.

virtual device. A device that appears to the user as a separate entity, but is actually a shared portion of a real device.

virtual device driver (VDD). Synonym for device handler.

virtual file system (VFS). A remote file system that has been mounted so that it is accessible to the local user.

virtual function. A C++ member function that is declared with the keyword virtual. The implementation that is executed when you make a call to a virtual function depends on the type of the object for which it is called. This is determined at run time.

virtual key binding. In AIXwindows, the user-designed key definitions.

virtual memory. Addressable space that appears to be real storage. From virtual storage, instructions and data are mapped into real storage locations. The size of virtual storage is limited by the addressing scheme of the computer system and by the amount of auxiliary storage available, not by the actual number of system memory locations. Contrast with real memory. Synonymous with virtual storage.

virtual mount point. The directory or file in the file tree where another file system is mounted. For example, if /dev/hd9 is mounted on /fred, then /fred is the virtual mount point.

virtual printer. A view of a printer that refers only to the high-level data stream (such as ASCII or PostScript) that the printer understands. It does not include any information about how the printer hardware is attached to the host computer or the protocol used for transferring bytes of data to and from the printer.

virtual printer definition. A set of attributes values that describe a particular data stream for a particular printer.

virtual storage. Synonym for virtual memory.

Virtual Storage Extended (VSE). An operating system that is an extension of DOS. A VSE system consists of licensed VSE/Advanced Functions support plus all programs required to meet the data processing needs of the user. Together with the hardware it controls, VSE forms a complete data processing system. Its current version is called VSE/ESA.

Virtual Storage Extended/Enterprise Systems Architecture(VSE/ESA). The VSE operating system operating in an ESA environment. ESA is an extension to the System/370 architecture and includes an advanced addressability feature that provides access registers.

Virtual Storage Extended/System Product (VSE/SP). A licensed program providing VSE operating system support.

Virtual Telecommunication Access Method (VTAM). A licensed program that controls communication and data flow in an SNA network. It provides single-domain, multiple-domain, and interconnected network capability, and also supports application programs and subsystems.

visibility. In Ada language, at a given point in a program text, the declaration of an entity with a certain identifier is said to be visible if the entity is an acceptable meaning for an occurrence at that point of the identifier. The declaration is visible by selection at the place of the selector in a selected component or at the place of the name in a named association. Otherwise, the declaration is directly visible, that is, if the identifier alone has that meaning.

visible. (1.) A region of a window that is mapped and not occluded on the screen by another window. (2.) Visibility of C++ identifiers is based on scoping rules and is independent of access.

visible part. For Ada programming, see package.

VLSI. Very large scale integration.

VLSI circuit. Very large scale integrated circuit.

VLT. See video lookup table.

VM. Virtual machine.

VM/CMS. A type of operating system used on a System/370 computer.

VMTP. See Versatile Message Transaction Protocol.

VOL. See Volume Service.

Vol ID. See Volume ID.

volatile attribute. The keyword volatile located in a definition, declaration, or cast. It causes the C language compiler to place the value of the data object in storage and to reload this value at each reference to the data object.

volatile register. In a C language program, a register whose value on entry need not be preserved when the called routine returns.

volume. (1.) A certain portion of data, together with its data carrier, that can be handled conveniently as a unit. (2.) The level of sound of the system. (3.) The physical storage location of a file system. See also log volume.

volume group (VG). A set of one or more physical volumes from which space can be allocated to one or more logical volumes. A collection of 1 to 32 physical volumes (read-write fixed-disk drives) of varying size and type. See also logical volume.

Volume ID (Vol ID). A series of characters, recorded on the diskette, used to identify the diskette to the user and to the system.

volume label. An area on tape or disk that is used to identify the tape volume and its owner.

Volume Service (VOL). The component of Encina Base that addresses storage.

VPD. See Software Vital Product Data (SWVPD).

VPI. Virtual path identifier in an ATM network.

VRAM. Video random-access memory.

VSE. See Virtual Storage Extended.

VSE/ESA. See Virtual Storage Extended/Enterprise Systems Architecture.

VSE/SP. See Virtual Storage Extended/System Product.

VTAM. See Virtual Telecommunication Access Method.

VTL. Vendor Technology Logic.

[ Previous | Next Page | Table of Contents | Library Home | Legal | Search ]