[Sun Users' Group & elsewhere]
n. 1. Software EXchange. A technique invented by the blue-green algae hundreds of millions of years ago to speed up their evolution, which had been terribly slow up until then. Today, SEX parties are popular among hackers and others (of course, these are no longer limited to exchanges of genetic software). In general, SEX parties are a Good Thing, but unprotected SEX can propagate a virus.
See also pubic directory.
2. The rather Freudian mnemonic often used for Sign EXtend, a machine instruction found in the PDP-11 and many other architectures.
DEC's engineers nearly got a PDP-11 assembler that used the 'SEX' mnemonic out the door at one time, but (for once) marketing wasn't asleep and forced a change. That wasn't the last time this happened, either. The author of 'The Intel 8086 Primer', who was one of the original designers of the 8086, noted that there was originally a 'SEX' instruction on that processor, too. He says that Intel management got cold feet and decreed that it be changed, and thus the instruction was renamed 'CBW' and 'CWD' (depending on what was being extended). Amusingly, the Intel 8048 (the microcontroller used in IBM PC keyboards) is also missing straight 'SEX' but has logical-or and logical-and instructions 'ORL' and 'ANL'.
The Motorola 6809, used in the U.K.'s 'Dragon 32' personal computer, actually had an official 'SEX' instruction; the 6502 in the Apple II it competed with did not. British hackers thought this made perfect mythic sense; after all, it was commonly observed, you could have sex with a dragon, but you can't have sex with an apple.