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Data General AOS
Developer	Data General
Working state	Discontinued
Source model	Closed-source
Supported platforms	Data General16-bitEclipse C, M, and Sminicomputers and 32-bitEclipse MV line
Default user interface	Command-line interpreter
License	Proprietarycommercial software

Data General AOS (an abbreviation forAdvanced Operating System^[1]) was the name of a family ofoperating systems forData General16-bitEclipse C, M, and Sminicomputers, followed byAOS/VS and AOS/RT32^[2] (1980) and laterAOS/VS II (1988) for the 32-bitEclipse MV line.

AOS/VS exploited the 8-ring protection architecture of theEclipse MV hardware with ring 7 being the least privileged and ring 0 being the most privileged. The AOS/VS kernel ran in ring 0 and used ring-1 addresses for data structures related to virtual address translations. Ring 2 was unused and reserved for future use by the kernel. The Agent, which performed much of the system call validation for the AOS/VS kernel, as well as some I/O buffering and many compatibility functions, ran in ring 3 of each process. Ring 4 was used by various D.G. products such as the INFOS IIDBMS. Rings 5 and 6 were reserved for use by user programs but rarely used except for large software such as the MV/UX inner-ring emulator andOracle which used ring 5. All user programs ran in ring 7.

The AOS software was far more advanced than competingPDP-11 operating systems. 16-bit AOS applications ran natively under AOS/VS and AOS/VS II on the 32-bit Eclipse MV line. AOS/VS (Advanced Operating System/Virtual Storage) was the most commonly used DG software product, and included acommand-line interpreter (CLI) allowing for complex scripting, DUMP/LOAD, and other custom components.

The 16-bit version of the CLI is famous for including anEaster egg meant to honor Xyzzy (which was pronounced "magic"). This was the internal code name of what externally became known as the AOS/VS 32-bit operating system. A user typing in thecommand "xyzzy" would get back a response from the CLI of "Nothing Happens". When a32-bit version of the CLI became available underAOS/VS II, the same command instead reported "Twice As Much Happens".

A modified version of System V.2Unix called MV/UX hosted under AOS/VS was also available. A modified version ofSystem V Unix calledDG/UX was made for theEclipse MV line and later the88K andx86AViiON machines.

The AOS and AOS/VS kernels were written entirely inassembly language. Almost all of the AOS and AOS/VS utilities included in the operating system releases were written inDG/L a variant of theALGOL/60 programming language. Initially, AOS/VS utilities closely tracked AOS source development. As AOS/VS matured, many DG-supplied utilities were rewritten to take advantage of the 32-bit address space and reduce dependencies on assembly language, often resulting in substantial increases in functionality, performance and reliability compared with their AOS ancestors.

**** Atari S/W Development HCD1 / BATCH OUTPUT FILE ****AOS/VS  3.07 / EXEC  3.0719-JAN-8410:11:01QPRI=254SEQ=31324INPUT FILE -- :UDD:SYSTEMS:850:?031.CLI.004.JOB (WILL BE DELETED AFTER PROCESSING)LIST FILE  -- :QUEUE:NORDIN.LIST.31324--------LAST MESSAGE CHANGE12-JAN-8416:06:08Atari S/W Development System HCD1Backup schedule (system shut down): Saturday  21-Jan-84  9:30-11:30amRefer to HELP *COMMANDS, HELP *PSEUDO, HELP, APHELP, and ?MHELP.Refer to DISP FUNC in SED for list of default function key commands.--------LAST PREVIOUS LOGON19-JAN-8410:09:45* searchlist :UDD:NORDIN:UTIL :UDD:NORDIN:LINKS :C :UTIL :AOS/VS CLI   REV 03.03.00.0019-JAN-8410:11:05Ý SEARCHLIST :UDD:SYSTEMS:UTIL,:UDD:NORDIN:UTIL,:UDD:NORDIN:LINKS,:C,:UTIL,:Ý DIRECTORY :UDD:SYSTEMS:850Ý DEFACL SYSTEMS,OWARE,A.JOE,OWARE,A.OLIVIA,OWARE,ARKEN,OWARE,BLOTCKY,OWARE,NORDIN,OWARE,TITTSLER,OWARE,FOWKES,OWAREÝ CAMAC R850AMAC H=R850AMAC.OBJ L=R850AMAC.PRN R=F SL=132 ATARI CAMAC Assembler Ver  1.0ACopyright 1981 ATARI Inc.Enter source file name and optionsd:R850AMAC  h=d:R850AMAC.OBJ l=d:R850AMAC.PRN R=F SL=132             Pass 1 - Reading D1:R850AMAC.     Pass 2 - Reading D1:R850AMAC.     no ERRORs,  669 Labels, $67E8 free.�ATARI CAMAC Assembler Ver  1.0ACopyright 1981 ATARI Inc.Enter source file name and optionsÝ Ý END OF FILEAOS/VS CLI   TERMINATING19-JAN-8410:12:06PROCESS 42 TERMINATED ELAPSED TIME  0:01:06(OTHER JOBS, SAME USERNAME)USER 'NORDIN' LOGGED OFF 19-JAN-8410:12:07***** LIST FILE EMPTY, WILL NOT BE PRINTED****

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