SEX (computing)

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The acronym SEX (written in capital letters) redirects here. For other meanings, see Sex (disambiguation).

In computing, the SEX assembly language mnemonic has often been used for the "Sign EXtend" machine instruction found in the PDP-11 and many other computer architectures.

[edit] SEX as an assembly language mnemonic

DEC's engineers nearly got a PDP-11 assembler (MACRO-11) that used the SEX mnemonic (for Sign EXtend) out the door at one time, however their marketing department forced them to change it to SXT before release.

The RCA 1802 chip used in the early ELF and ELF II microcomputers had a "SEt X register"  instruction, but this seems to have had little folkloric impact, probably because of the 1802's very low market share in the general microcomputer field.

The Motorola 6809, used in Radio Shack's TRS-80 Color Computer (in the US) and Dragon Data's Dragon 32/64 home/personal computers (in the UK), actually had an official SEX instruction; the MOS 6502 in the Apple II and the Commodore VIC-20 with which it competed did not. British hackers thought this made perfect mythic sense; after all, it was commonly observed, you could (on some theoretical level) have sex with a dragon, but you can't have sex with an apple.^{[citation needed]}

The author of The Intel 8086 Primer, who was one of the original designers of the Intel 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). The Intel 8048 microcontroller (used e.g. in the original IBM PC keyboard) is also missing straight SEX but has logical-or and logical-and instructions ORL and ANL.

In NEC's SX architecture, the SEX instruction stands for "Save EXecution counter". The Execution Counter increments once for every SX instruction executed.

[edit] SEX in software: rarely used jargon

The TLA SEX has humorously been said to stand for Software EXchange, meaning copying of software. As file sharing has sometimes spread computer viruses, it has been stated that “illicit SEX can transmit viral diseases to your computer.”

[edit] Other sightings

The Commodore 64 Video Interface Chip (VIC) II contains registers to double the size of the hardware sprites in one or both directions. The register $d017 (Sprite EXpand Y) contains 1 bit per sprite to allow expansion in the Y direction, while $d01d (Sprite EXpand X) alters the X size in the same manner.

This article is based in part on the Jargon File, which is in the public domain.