:patch: 1. n. A temporary addition to a piece of code, usually as a {quick-and-dirty} remedy to an existing bug or misfeature. A patch may or may not work, and may or may not eventually be incorporated permanently into the program. Distinguished from a {diff} or {mod} by the fact that a patch is generated by more primitive means than the rest of the program; the classical examples are instructions modified by using the front panel switches, and changes made directly to the binary executable of a program originally written in an {HLL}. Compare {one-line fix}. 2. vt. To insert a patch into a piece of code. 3. [in the UNIX world] n. A {diff} (sense 2). 4. A set of modifications to binaries to be applied by a patching program. IBM operating systems often receive updates to the operating system in the form of absolute hexadecimal patches. If you have modified your OS, you have to disassemble these back to the source. The patches might later be corrected by other patches on top of them (patches were said to "grow scar tissue"). The result was often a convoluted {patch space} and headaches galore. 5. [UNIX] the `patch(1)' program, written by Larry Wall, which automatically applies a patch (sense 3) to a set of source code.
There is a classic story of a {tiger team} penetrating a secure military computer that illustrates the danger inherent in binary patches (or, indeed, any that you can't —- or don't —- inspect and examine before installing). They couldn't find any {trap door}s or any way to penetrate security of IBM's OS, so they made a site visit to an IBM office (remember, these were official military types who were purportedly on official business), swiped some IBM stationery, and created a fake patch. The patch was actually the trapdoor they needed. The patch was distributed at about the right time for an IBM patch, had official stationery and all accompanying documentation, and was dutifully installed. The installation manager very shortly thereafter learned something about proper procedures.
:patch space: n. An unused block of bits left in a binary so that it can later be modified by insertion of machine-language instructions there (typically, the patch space is modified to contain new code, and the superseded code is patched to contain a jump or call to the patch space). The widening use of HLLs has made this term rare; it is now primarily historical outside IBM shops. See {patch} (sense 4), {zap} (sense 4), {hook}.
: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 that they will happen so infrequently (if at all) that there is no justification for going to extra trouble to handle that case (see sense 1).
:payware: /pay'weir/ n. Commercial software. Oppose {shareware} or {freeware}.
:PBD: /P-B-D/ [abbrev. of `Programmer Brain Damage'] n. 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: /pid'l/ or /puhd'l/ [abbreviation for `Push Down List'] 1. n. In ITS days, the preferred MITism for {stack}. See {overflow pdl}. 2. n. Dave Lebling, one of the co-authors of {Zork}; (his {network address} on the ITS machines was at one time pdl@dms). 3. n. `Program Design Language'. Any of a large class of formal and profoundly useless pseudo-languages in which {management} forces one to design programs. {Management} often expects it to be maintained in parallel with the code. See also {{flowchart}}. 4. v. To design using a program design language. "I've been pdling so long my eyes won't focus beyond 2 feet." 5. 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.