Data General AOS

Data General wrote operating systems for its hardware: DOS and RDOS for the 16-bit Nova line; RDOS and AOS for the 16-bit Eclipse C, M and S lines; AOS/VS (1980) and later AOS/VS II (1988), AOS/RT32 (1988) for the 32-bit Eclipse MV line.

A modified version of System V.2 Unix called MV/UX hosted under AOS/VS was also available. A modified version of System V Unix called DG/UX was made for the Eclipse MV line and later the 88K and x86 AViiON machines.

The AOS software was far more advanced than competing PDP-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 was the most commonly used DG software product, and included a command-line interpreter (CLI) allowing for complex scripting, DUMP/LOAD, and other custom components.

The 16-bit version of the CLI is famous for including an Easter egg taken directly from the Colossal Cave Adventure game. A user typing in the command "xyzzy" would get back a response from the CLI of "Nothing Happens".

When a 32-bit version of the CLI became available under AOS/VS II, the same command instead reported "Twice As Much Happens".

AOS/VS exploited the 8-ring architecture of the Eclipse MV hardware with ring-7 being the least privileged and ring-0 being the most privileged. The AOS/VS kernel ran in ring-0. The Agent ran in ring-3. Ring 4 was used by various D.G. products such as the INFOS II DBMS. Rings 5-6 were reserved for use by user programs but rarely used except for large software such as the MV/UX inner-ring emulator and Oracle which used ring-5. All user programs ran in ring-7.