High Performance Computing and Communications Glossary 2.1

A significant part of the material of this glossary was adapted from material originally written by Gregory V. Wilson which appeared as "A Glossary of Parallel Computing Terminology" (IEEE Parallel & Distributed Technology, February 1993), and is being re-printed in the same author's "Practical Parallel Programming" (MIT Press, 1995). Several people have contributed additions to this glossary, especially Jack Dongarra, Geoffrey Fox and many of my colleagues at Edinburgh and Syracuse.

Original version is from NPAC at <URL:http://nhse.npac.syr.edu/hpccgloss/>

Original author: Ken Hawick, khawick@cs.adelaide.edu.au

See also the index of all letters and the full list of entries (very large)

Sections: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


V.35 (n.) A data communications interface standard adopted for use with circuits 56Kbps and above.

valence (n.) The number of edges connected to a vertex in a graph; for example, every node in a regular square mesh has a valence of 4. Confusingly, valence also means the number of branches below a tree node, which is one fewer than the number of edges incident to that node - every node in a binary tree has a valence of 2. The term arity is sometimes also used in this sense.

vector (n.) an ordered list of items in a computer's memory. A simple vector is defined as having a starting address, a length, and a stride. An indirect address vector is defined as having a relative base address and a vector of values to be applied as indices to the base.

vector processor (n.) A computer designed to apply arithmetic operations to long vectors or arrays. Most vector processors rely heavily on pipelining to achieve high performance. See also array processor.

vector register (n.) a storage device that acts as an intermediate memory between a computer's functional units and main memory.

vectorize (v.) To transform a sequence of identical arithmetic operations into a single instruction. See also array processor, vector processor.

vertex (n.) component of a graph, also sometimes called a node.

vertical processing (n.) processing a two dimensional array column by column.

virtual channel (n.) A logical point-to-point connection between two processes. Many virtual channels may time share a single link to hide latency and to avoid deadlock. See also wormhole routing.

virtual concurrent computer (n.) A computer system that is programmed as a concurrent computer of some number of nodes P, but which is implemented on either a real concurrent computer of some number of nodes less than P or on a uniprocessor running software to emulate the environment of a concurrent machine. Such an emulation system is said to provide virtual nodes to the user.

virtual cut-through (n.) A technique for routing messages in which the head and tail of the message both proceed as rapidly as they can. If the head is blocked because a link it wants to cross is being used by some other message, the tail continues to advance, and the message's contents are put into buffers on intermediate nodes. See also packet switching, wormhole routing.

virtual memory (n.) A system that stores portions of an address space that are not being actively used in in some medium other than main high-speed memory, such as a disk or slower auxiliary memory medium. When a reference is made to a value not presently in main memory, the virtual memory manager must swap some values in main memory for the values required. Virtual memory is used by almost all uniprocessors and multiprocessors, but is not available on some array processors and multicomputers, which still employ real memory storage only on each node.

virtual shared memory (n.) Memory that appears to users to constitute a single address space, but which is actually physically disjoint. Virtual shared memory is often implemented using some combination of hashing and local caching.

VLIW (n.) Very Long Instruction Word; the use of extremely long instructions (256 bits or more) in a computer to improve its ability to chain operations together.

VLSI (adj.) Very Large Scale Integration; applied to technologies capable of putting hundreds of thousands or more components on a single chip, or sometimes applied to those chips so manufactured.

VMS (n.) Virtual Machine System; an operating system developed by DEC and widely used on VAX machines. Popularity of this OS is probably waning in favour of UNIX like systems.

Von Neumann architecture (n.) Used to describe any computer which does not employ concurrency or parallelism. Named after John Von Neumann (1903-1957) who is credited with the invention of the basic architecture of current sequential computers.