Computing Dictionary

AOS definition

1. /aws/ (East Coast), /ay-os/ (West Coast) A PDP-10 instruction that took any memory location and added 1 to it. AOS meant "Add One and do not Skip". Why, you may ask, does the "S" stand for "do not Skip" rather than for "Skip"? Ah, here was a beloved piece of PDP-10 folklore. There were eight such instructions: AOSE added 1 and then skipped the next instruction if the result was Equal to zero; AOSG added 1 and then skipped if the result was Greater than 0; AOSN added 1 and then skipped if the result was Not 0; AOSA added 1 and then skipped Always; and so on. Just plain AOS didn't say when to skip, so it never skipped.
For similar reasons, AOJ meant "Add One and do not Jump". Even more bizarre, SKIP meant "do not SKIP"! If you wanted to skip the next instruction, you had to say "SKIPA". Likewise, JUMP meant "do not JUMP"; the unconditional form was JUMPA. However, hackers never did this. By some quirk of the 10's design, the JRST (Jump and ReSTore flag with no flag specified) was actually faster and so was invariably used. Such were the perverse mysteries of assembler programming.
2. /A-O-S/ or /A-os/ A Multics-derived operating system supported at one time by Data General.
3. Algebraic Operating System, in reference to those calculators which use infix operators instead of postfix notation.
[Jargon File]

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American Heritage
Abbreviations & Acronyms
  1. Academic Orthopaedic Society

  2. acquisition of signal

  3. American Otological Society

The American Heritage® Abbreviations Dictionary, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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