Apple GS/OS

GS/OS is an operating system developed by Apple Computer for its Apple IIGS personal computer that uses the ProDOS filing system. It provides facilities for accessing the file system, controlling input/output devices, loading and running program files, and a system allowing programs to handle interrupts and signals. GS/OS was included as a component of Apple IIGS System Software versions 4.0 through 6.0.1. GS/OS, unlike its predecessor, is written entirely in 16-bit code and was the first true 16-bit operating system for the IIGS.

GS/OS running.
DeveloperApple Computer
OS familyGS/OS
Working stateHistoric
Source modelClosed source
Initial release1988 (1988)
Latest releaseGS/OS v4.02 (System Software 6.0.1) / May 6, 1993 (1993-05-06)
Kernel typeMonolithic kernel
LicenseApple Software License Agreement

GS/OS includes a facility known as file system translators (FSTs) which allows it to support multiple on-disk file systems in a manner transparent to application programs, a feature not found in ProDOS or most other microcomputer operating systems at the time. It was usually used with the ProDOS file system (which was the only one from which it could be booted), but GS/OS also supports a variety of other file systems, including the Hierarchical File System used by the Mac OS. Other file system translators, in addition to ProDOS and HFS, include those for MS-DOS, High Sierra/ISO-9660, Apple DOS 3.3, and Pascal, albeit read-only (full read/write support had been planned but never completed). Another advantage of GS/OS over ProDOS 16 is that it was written in 16-bit code for the 65816 processor used in the IIGS, rather than primarily in 8-bit 6502 machine code that does not take advantage of the IIGS's unique features. It also extends the ProDOS file system to provide for resource forks on files similar to those used on the Apple Macintosh, which allows for programs to be written in a more flexible way.

The big change from the previous versions of ProDOS is that GS/OS incorporates many features of the Macintosh System 5. In particular, GS/OS has a Finder, loadable fonts, plug-in device drivers (modem, printer, etc.).[1] A command-line development environment called APW (Apple Programmer's Workshop) is available; much like the Macintosh Programmer's Workshop.[2][3][4]


ProDOS 16 (GS/OS predecessor)

  • 1986 – System 1.0 (ProDOS 16 v1.0), System 1.1 (ProDOS 16 v1.1)
  • 1987 – System 2.0 (ProDOS 16 v1.2), System 3.1 (ProDOS 16 v1.3)
  • 1988 – System 3.2 (ProDOS 16 v1.6)


  • 1988 – System 4.0 (GS/OS v2.0)
  • 1989 – System 5.0 (GS/OS v3.0), System 5.0.2 (GS/OS v3.0)
  • 1990 – System 5.0.3 (GS/OS v3.03)
  • 1991 – System 5.0.4 (GS/OS v3.03)
  • 1992 – System 6.0 (GS/OS v4.01)
  • 1993 – System 6.0.1 (GS/OS v4.02)

Unofficial versions

  • 2015 – System 6.0.2 (GS/OS v4.02),[6] System 6.0.3 (GS/OS v4.02)[7]
  • 2017 – System 6.0.4 (GS/OS v4.02)[8]

See also


  1. Arnett, Nick (1988-09-19). "Apple Unveils IIGS OS, Speedier Apple IIc Model". InfoWorld. Vol. 10 no. 38. IDG. p. 39. ISSN 0199-6649. Retrieved 2016-08-03. ...Apple Computer last week introduced a new operating system for the Apple IIGS,.....The new GS/OS operating system for the Apple IIGS has an enhanced, more Mac-like Finder and speeds up booting......includes support for large storage devices, up to 4 gigabytes...GS/OS runs programs written for the earlier operating systems, Pro-Dos 16 and Pro-Dos 8...
  2. "Apple IIGS Programmer's Workshop - Version 1.0 (K2S002)" (PDF). Retrieved 2016-08-03. ...APW C is intended for use with the Apple Programmer's Workshop...
  3. "Morgue, Cortland Programmer's Workshop". Retrieved 2016-08-03. ...Apple decided to use a 16 bit version of ORCA/M as the standard development environment for the new machine, code named Cortland. On July 21, 1986, the last version of this environment that was still called Cortland Programmer’s Workshop was delivered to Apple for shipment to the developer community. Later versions were called Apple Programmer’s Workshop, or just APW...
  4. Westerfield, Mike (2013). "About the Author". Building IPhone and IPad Electronic Projects: Real-World Arduino, Sensor, and Bluetooth Low Energy Apps in TechBASIC. Beijing: O'Reilly Media. p. 317. ISBN 1449363482. Retrieved 2016-08-03. ...Mike Westerfield...Two years later he finished ORCA/M, which went on to become Apple Programmer's Workshop, the Apple development environment for the Apple IIGS...
  5. "GUIdebook > ... > Apple II > GS/OS". Retrieved 2016-08-03.
  6. "Announcing Apple IIgs System 6.0.2". 2015-07-12. Retrieved 2016-08-03.
  7. "The Source Awakens .. System 6.0.3, a New Release". 2015-08-03. Retrieved 2016-08-03.
  8. "The Source Is Strong With This One – System 6.0.4". Retrieved 2017-01-04.
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