:path: /n./ 1. A {bang path} or explicitly routed {{Internet address}}; a node-by-node specification of a link between two machines. 2. [Unix] A filename, fully specified relative to the root directory (as opposed to relative to the current directory; the latter is sometimes called a `relative path'). This is also called a `pathname'. 3. [Unix and MS-DOS] The `search path', an environment variable specifying the directories in which the {shell} (COMMAND.COM, under MS-DOS) should look for commands. Other, similar constructs abound under Unix (for example, the C preprocessor has a `search path' it uses in looking for `#include' files).
:pathological: /adj./ 1. [scientific computation] Used of a data set that is grossly atypical of normal expected input, esp. one that exposes a weakness or bug in whatever algorithm one is using. An algorithm that can be broken by pathological inputs may still be useful if such inputs are very unlikely to occur in practice. 2. When used of test input, implies that it was purposefully engineered as a worst case. The implication in both senses is that the data is spectacularly ill-conditioned or that someone had to explicitly set out to break the algorithm in order to come up with such a crazy example. 3. Also said of an unlikely collection of circumstances. "If the network is down and comes up halfway through the execution of that command by root, the system may just crash." "Yes, but that's a pathological case." Often used to dismiss the case from discussion, with the implication that the consequences are acceptable, since they will happen so infrequently (if at all) that it doesn't seem worth going to the extra trouble to handle that case (see sense 1).
:payware: /pay'weir/ /n./ Commercial software. Oppose {shareware} or {freeware}.
:PBD: /P-B-D/ /n./ [abbrev. of `Programmer Brain Damage']
Applied to bug reports revealing places where the program was
obviously broken by an incompetent or short-sighted programmer.
Compare {UBD}; see also {brain-damaged}.
:PC-ism: /P-C-izm/ /n./ A piece of code or coding technique that takes advantage of the unprotected single-tasking environment in IBM PCs and the like, e.g., by busy-waiting on a hardware register, direct diddling of screen memory, or using hard timing loops. Compare {ill-behaved}, {vaxism}, {unixism}. Also, `PC-ware' n., a program full of PC-isms on a machine with a more capable operating system. Pejorative.
:PD: /P-D/ /adj./ Common abbreviation for `public domain', applied to software distributed over {Usenet} and from Internet archive sites. Much of this software is not in fact public domain in the legal sense but travels under various copyrights granting reproduction and use rights to anyone who can {snarf} a copy. See {copyleft}.
:PDL: /P-D-L/, /pid'l/, /p*d'l/ or /puhd'l/ 1. /n./ `Program Design Language'. Any of a large class of formal and profoundly useless pseudo-languages in which {management} forces one to design programs. Too often, management expects PDL descriptions to be maintained in parallel with the code, imposing massive overhead to little or no benefit. See also {{flowchart}}. 2. /v./ To design using a program design language. "I've been pdling so long my eyes won't focus beyond 2 feet." 3. /n./ `Page Description Language'. Refers to any language which is used to control a graphics device, usually a laserprinter. The most common example is, of course, Adobe's {{PostScript}} language, but there are many others, such as Xerox InterPress, etc.
:pdl: /pid'l/ or /puhd'l/ /n./ [abbreviation for `Push Down List'] 1. In ITS days, the preferred MITism for {stack}. See {overflow pdl}. 2. Dave Lebling, one of the co-authors of {Zork}; (his {network address} on the ITS machines was at one time pdl@dms). 3. Rarely, any sense of {PDL}, as these are not invariably capitalized.
:PDP-10: /n./ [Programmed Data Processor model 10] The machine that made timesharing real. It looms large in hacker folklore because of its adoption in the mid-1970s by many university computing facilities and research labs, including the MIT AI Lab, Stanford, and CMU. Some aspects of the instruction set (most notably the bit-field instructions) are still considered unsurpassed. The 10 was eventually eclipsed by the VAX machines (descendants of the PDP-11) when DEC recognized that the 10 and VAX product lines were competing with each other and decided to concentrate its software development effort on the more profitable VAX. The machine was finally dropped from DEC's line in 1983, following the failure of the Jupiter Project at DEC to build a viable new model. (Some attempts by other companies to market clones came to nothing; see {Foonly} and {Mars}.) This event spelled the doom of {{ITS}} and the technical cultures that had spawned the original Jargon File, but by mid-1991 it had become something of a badge of honorable old-timerhood among hackers to have cut one's teeth on a PDP-10. See {{TOPS-10}}, {{ITS}}, {AOS}, {BLT}, {DDT}, {DPB}, {EXCH}, {HAKMEM}, {JFCL}, {LDB}, {pop}, {push}.
:PDP-20: /n./ The most famous computer that never was. {PDP-10} computers running the {{TOPS-10}} operating system were labeled `DECsystem-10' as a way of differentiating them from the PDP-11. Later on, those systems running {TOPS-20} were labeled `DECSYSTEM-20' (the block capitals being the result of a lawsuit brought against DEC by Singer, which once made a computer called `system-10'), but contrary to popular lore there was never a `PDP-20'; the only difference between a 10 and a 20 was the operating system and the color of the paint. Most (but not all) machines sold to run TOPS-10 were painted `Basil Blue', whereas most TOPS-20 machines were painted `Chinese Red' (often mistakenly called orange).