:orphan: /n./ [Unix] A process whose parent has died; one inherited by `init(1)'. Compare {zombie}.
:orphaned i-node: /or'f*nd i:'nohd/ /n./ [Unix] 1. [techspeak] A file that retains storage but no longer appears in the directories of a filesystem. 2. By extension, a pejorative for any person no longer serving a useful function within some organization, esp. {lion food} without subordinates.
:orthogonal: /adj./ [from mathematics] Mutually independent; well separated; sometimes, irrelevant to. Used in a generalization of its mathematical meaning to describe sets of primitives or capabilities that, like a vector basis in geometry, span the entire `capability space' of the system and are in some sense non-overlapping or mutually independent. For example, in architectures such as the PDP-11 or VAX where all or nearly all registers can be used interchangeably in any role with respect to any instruction, the register set is said to be orthogonal. Or, in logic, the set of operators `not' and `or' is orthogonal, but the set `nand', `or', and `not' is not (because any one of these can be expressed in terms of the others). Also used in comments on human discourse: "This may be orthogonal to the discussion, but…."
:OS: /O-S/ 1. [Operating System] /n./ An abbreviation heavily used in email, occasionally in speech. 2. /n. obs./ On ITS, an output spy. See "{OS and JEDGAR}" in Appendix A.
:OS/2: /O S too/ /n./ The anointed successor to MS-DOS for Intel 286- and 386-based micros; proof that IBM/Microsoft couldn't get it right the second time, either. Often called `Half-an-OS'. Mentioning it is usually good for a cheap laugh among hackers —- the design was so {baroque}, and the implementation of 1.x so bad, that 3 years after introduction you could still count the major {app}s shipping for it on the fingers of two hands — in unary. The 2.x versions are said to have improved somewhat, and informed hackers now rate them superior to Microsoft Windows (an endorsement which, however, could easily be construed as damning with faint praise). See {monstrosity}, {cretinous}, {second-system effect}.
:OSU: /O-S-U/ /n. obs./ [TMRC] Acronym for Officially Sanctioned User; a user who is recognized as such by the computer authorities and allowed to use the computer above the objections of the security monitor.
:OTOH: // [USENET] On The Other Hand.
:out-of-band: /adj./ [from telecommunications and network theory] 1. In software, describes values of a function which are not in its `natural' range of return values, but are rather signals that some kind of exception has occurred. Many C functions, for example, return a nonnegative integral value, but indicate failure with an out-of-band return value of -1. Compare {hidden flag}, {green bytes}, {fence}. 2. Also sometimes used to describe what communications people call `shift characters', such as the ESC that leads control sequences for many terminals, or the level shift indicators in the old 5-bit Baudot codes. 3. In personal communication, using methods other than email, such as telephones or {snail-mail}.
:overflow bit: /n./ 1. [techspeak] A {flag} on some processors indicating an attempt to calculate a result too large for a register to hold. 2. More generally, an indication of any kind of capacity overload condition. "Well, the {{Ada}} description was {baroque} all right, but I could hack it OK until they got to the exception handling … that set my overflow bit." 3. The hypothetical bit that will be set if a hacker doesn't get to make a trip to the Room of Porcelain Fixtures: "I'd better process an internal interrupt before the overflow bit gets set".
:overflow pdl: /n./ [MIT] The place where you put things when your {pdl} is full. If you don't have one and too many things get pushed, you forget something. The overflow pdl for a person's memory might be a memo pad. This usage inspired the following doggerel: