Online Computer Terms Dictionary - P

Parallel C

1. <language, parallel> Never implemented, but influenced the design of C*. [Details?]

2. C for the transputer by 3L.

3. (PC) Extensions to C developed at the University of Houston providing a shared memory SIMD model on message passing computers.

ftp://karazm.math.uh.edu/pub/Parallel/Tools/pc.1.1.1.tar.Z.

E-mail: Ridgway Scott <scott@uh.edu>.

(1995-03-21)

parallel computer

parallel processor

parallel computing

parallel processing

Parallel FORTH

Forth For the MPP.

Parallel Fortran

<language> (Pfortran) Extensions to Fortran by Ridgway Scott <scott@uh.edu> of Houston University. Pfortran provides a shared memory SIMD model on message passing computers.

It was under development in 1994.

["Pfortran: A Parallel Dialect of Fortran", L.R. Scott, Fortran Forum 11(3):20-31, Sep 1992].

(1994-11-08)

Parallel Haskell

<language, parallel> (pH) A parallel variant of Haskell incorporating ideas from Id and Sisal. pH is under development.

Mailing list: pH@abp.lcs.mit.edu.

(1995-03-31)

parallelism

1. parallel processing.

2. <parallel> The maximum number of independent subtasks in a given task at a given point in its execution. E.g. in computing the expression

	(a + b) *

The Bernstein condition states that processes P and Q can be executed in parallel (or in either sequential order) only if:

(i) there is no overlap between the inputs of P and the outputs of Q and vice versa and

(ii) there is no overlap between the outputs of P, the outputs of Q and the inputs of any other task.

If process P outputs value v which process Q reads then P must be executed before Q. If both processes write to some variable then its final value will depend on their execution order so they cannot be executed in parallel if any other process depends on that variable's value.

(1995-05-07)

Parallel Pascal

<language> A data-parallel language, similar to Actus and Glypnir.

["Parallel Pascal: An Extended Pascal for Parallel Computers", A. Reeves, J Parallel Dist Computing 1:64-80 (1984)].

(1995-05-07)

parallel port

<hardware> An interface from a computer system where data is transferred in or out in parallel, that is, on more than one wire. A parallel port carries one bit on each wire thus multiplying the transfer rate obtainable over a single wire. There will usually be some control signals on the port as well to say when data is ready to be sent or received.

The commonest kind of parallel port is a printer port, e.g. a Centronics port which transfers eight bits at a time. Disks are also connected via special parallel ports, e.g. SCSI or IDE.

(1995-01-24)

Parallel Presence Detect

 {presence detect}

parallel processing

<parallel> (Or "multiprocessing") The simultaneous use of more than one computer to solve a problem. There are many different kinds of parallel computer (or "parallel processor"). They are distinguished by the kind of interconnection between processors (known as "processing elements" or PEs) and between processors and memory. Flynn's taxonomy also classifies parallel (and serial) computers according to whether all processors execute the same instructions at the same time ("single instruction/multiple data" - SIMD) or each processor executes different instructions ("multiple instruction/multiple data" - MIMD).

The processors may either communicate in order to be able to cooperate in solving a problem or they may run completely independently, possibly under the control of another processor which distributes work to the others and collects results from them (a "processor farm"). The difficulty of cooperative problem solving is aptly demonstrated by the following dubious reasoning:

	If it takes one man one minute to dig a post-hole
	then sixty men can dig it in one second.

Processors communicate via some kind of network or bus or a combination of both. Memory may be either shared memory (all processors have equal access to all memory) or private (each processor has its own memory - "distributed memory") or a combination of both.

Many different software systems have been designed for programming parallel computers, both at the operating system and programming language level. These systems must provide mechanisms for partitioning the overall problem into separate tasks and allocating tasks to processors. Such mechanisms may provide either implicit parallelism - the system (the compiler or some other program) partitions the problem and allocates tasks to processors automatically or explicit parallelism where the programmer must annotate his program to show how it is to be partitioned. It is also usual to provide synchronisation primitives such as semaphores and monitors to allow processes to share resources without conflict.

Load balancing attempts to keep all processors busy by allocating new tasks, or by moving existing tasks between processors, according to some algorithm.

Communication between tasks may be either via shared memory or message passing. Either may be implemented in terms of the other and in fact, at the lowest level, shared memory uses message passing since the address and data signals which flow between processor and memory may be considered as messages.

The terms "parallel processing" and "multiprocessing" imply multiple processors working on one task whereas "concurrent processing" and "multitasking" imply a single processor sharing its time between several tasks.

See also cellular automaton,symmetric multi-processing.

Usenet newsgroup: comp.parallel.

Institutions, research groups.

(2004-11-07)

parallel processor

<parallel> A computer with more than one central processing unit, used for parallel processing.

(1996-04-23)

parallel random access machine

<parallel> (PRAM) An idealised parallel processor consisting of P processors, unbounded shared memory, and a common clock. Each processor is a random access machine (RAM) consisting of R registers, a program counter, and a read-only signature register. Each RAM has an identical program, but the RAMs can branch to different parts of the program. The RAMs execute the program synchronously one instruction in one clock cycle.

See also pm2.

(1997-06-04)

parallel reduction

A form of applicative order reduction in which all redexes in an expression are reduced simultaneously. Variants include parallel outermost reduction and lenient reduction. See normal order reduction.

Parallel Server Option

Oracle Parallel Server

Parallel SML

["Parallel SML: A Functional Language and its Implementation in Dactl", Kevin Hammond, Pitman Press 1990].

Parallel Sysplex

<operating system> A Sysplex that uses one or more coupling facilities.

Home.

(1996-11-21)

Parallel Virtual Machine

<parallel, networking, tool> (PVM) 1. A software system designed to allow a network of heterogeneous machines to be used as a single distributed parallel processor.

PVM was developed by the University of Tennessee, The Oak Ridge National Laboratory and the Emory University.

Home.

Usenet newsgroup: comp.parallel.pvm.

2. The intermediate language used by the Gambit compiler for Scheme.

[And Multilisp?]

(1995-01-30)