Dictionary of Computer Terms


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XPC . eXplicitly Parallel C. A dialect of {Parallel C} which is efficiently compilable to both {SIMD} and {MIMD} architectures. Only research implementations exist. ["Toward Semantic Self-Consistency in Explicitly Parallel Languages," M.J. Phillip & H.G. Dietz, Proc 4th Intl Conf on Supercomputing, Santa Clara, CA, May 1989, v.1, pp.398-407]. (1994-12-01)
XperCASE . A structure diagram editor for developing, re-engineering, maintaining and documenting programs, developed by {Siemens} AG, Austria. It runs under {Microsoft Windows}. {(ftp://src.doc.ic.ac.uk/computing/systems/ibmpc/simtel/windows3/xperspx1.zip)}. E-Mail: <[email protected]>. (1994-12-01)
XPG . {X/open Portability Guide}
XPG3 . Version 3 of the {X/open Portability Guide}.
XPL . A small dialect of {PL/I} used for compiler writing from Stanford, 1967-69. XPL has one-dimensional {array}s. I/O is achieved with character pseudo-variable INPUT and OUTPUT, e.g. It has inline {machine code}. "Programmers are given all the rope they ask for. Novices tend to hang themselves fairly frequently." XPL has been implemented on {IBM 360}, {Univac 1100}, {ICL System 4}, {CDC6000} and {Cyber} series, {XDS Sigma-5} and {Sigma-7} and {DEC} {PDP-10}. An optimising XPL compiler (version 1) by Robin Vowels is a standard implementation of XPL and is based on McKeeman, Horning, and Wortman's improved {XCOM} (which employs hashed symbol table generation). It includes the extra built-in function COREHALFWORD. The following areas have been optimised: procedures calls when the argument and corresponding parameter are of the same type, and when the argument is a constant; constant subscripts; use of CORELHALFWORD and COREWORD; string constants of length one; iterative DO statements by transferring code to the end of the loop. String constants of length one do not require a descriptor, hence more descriptors are available for string variables. Comparison operations are treated as commutative, and an improved Commute algorithm is used. Halfword instructions are generated for BIT(16) variables. These areas have been improved or re-written: calls on OUTPUT, catenation, integer-to-string conversion, multiply, divide, and MOD. An emitter for SS-type instructions has been added. The compiler achieves an 11% reduction in object code compiling itself, an 11% increase in compilation rate, a 55% increase in compilation speed when the $E toggle is set. Special treatment for catenating a string to an integer substantially decreases consumption of the free string area, and decreases string moves. The latter improvement is most noticeable on small core machines. Core requirements: less than the improved XCOM on which it is based (approx. 98000 bytes). Symbol table size is 468. Ported to {IBM} {System 370}. The compiler is written in XPL. The code generators are machine-specific. ["A Compiler Generator," W.M. McKeeman et al, P-H 1970]. [JCC, AFIPS 1968]. (1993-08-07)
xpm . X11 Pixmap. A {pixmap} image {file format} for the {X Window System}. (1995-04-28)
XPOP . An extensible {macro assembly} language with user-redefinable {grammar}, for use with {FAP}. ["XPOP: A Meta-language Without Metaphysics", M.I. Halpern, Proc FJCC 25:57-68, AFIPS (Fall 1964)]. (1995-04-28)
Xpress Transport Protocol . (XTP) A {transport layer} {protocol} for high-speed networks promoted by the {XTP Forum}. XTP provides protocol options for error control, {flow control}, and rate control. Instead of separate protocols for each type of communication, XTP controls {packet} exchange patterns to produce different models, e.g. reliable {datagrams}, {transactions}, unreliable {streams}, and reliable {multicast} connections. {XTP Home (http://www.ca.sandia.gov/xtp/)}. Contrast with {Transmission Control Protocol}. XTP does not employ {congestion} avoidance {algorithms}. (2003-03-22)
X protocol . A {standard} {protocol} used by {clients} (applications) and {servers} in the {X Window System} for exchanging requests for window operations. (1995-04-28)
xref . /X'ref/ 1. cross-reference. 2. A cross-reference generator tool by Jim Leinweber. (1985?) [{Jargon File}]
Based on The Free On-line Dictionary of Computing, Editor Denis Howe - © Denis Howe 1993
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