All the software which makes your system operate. I guess it’s technically referring to processes and not to frameworks/libraries. For example MacOSX is an Operating System (OS). A typical OS is responsible for handling files and processes (and all that that entails).

Many Systems on a PowerBook (55 OSs on one machine) [http://www.kernelthread.com/mac/vpc/]

Known Operating Systems

*Pre-Macintosh Apple OS

*DOS 3.1 - Apple’s first official release of DOS *DOS 3.2 *DOS 3.3 *UCSD Pascal System - ‘P-System’. Multiplatform environment allowing ‘write once, run anywhere’ Pascal programs. A forerunner to Java. It even used platform-independent bytecodes. Developed at the University of California, San Diego. *SOS/PRODOS - The operating system designed for the Apple III computer. *ProDOS - The successor of Apple DOS *ProDOS 8 - This is ProDOS renamed when ProDOS 16 came into existence. *ProDOS 16 - Released to accommodate the Apple IIGS *Apple GS/OS *Apple GS/OS SYSTEM 6 *Lisa OS - Ran the Apple Lisa [http://toastytech.com/guis/lisaos1LisaTour.html]

*Apple Macintosh OS

• System 1.0 - 6.0 - Macintosh OS Prior to System 7
• System 7.0 - 7.1 (Blue) - Introduced file sharing, aliases, AppleScript.
• System 7.5 - 7.5.5 (Capone)- Introduced systemwide drag’n’drop, a scriptable Finder, clipping files, systemwide styled text
• MacOS 7.6 (Harmony) - 7.5 with the bugs fixed. Required an ‘030 or ‘040 CPU with 32-bit-clean ROMs. This was the first MacOS version to drop support for any Mac model other than the original 128k / 512k.
• MacOS 8.0 - 8.1 (Tempo) - Introduced the ‘Platinum’ appearance, multithreaded Finder, reorganized ControlPanels layout, tabbed Finder windows. First version released after SteveJobs returned to Apple. MacOS 8.0 was originally slated to be System 7.7, but Jobs changed it. Only supported on PPC and 68040 CPUs.
• MacOS 8.5 - 8.6 (Allegro) - First PPC-only version. Introduced tear-off application palette, Sherlock 1, 32-bit icons, Navigation Services.
• MacOS 9.0 - 9.2.1 (Sonata) - Introduced Sherlock 2, bundle support. Toward the end of MacOS 9 development, focus shifted to MacOSX Classic mode support, as opposed to running it as a standalone OS.
• A/UX - The original Apple branded UNIX, ran on 68K Macs. Commando (originally from MPW) gave a nice UI to the standard unix commands. [I wouldn’t call Commando “nice” – MikeTrent]

*MAE - Macintosh Application Environment. Ran System 7 under A/UX, Solaris and HP-UX. A forerunner to Classic.

• Darwin - The core of Mac OS X (Runs on both PowerPC and some x86 hardware)
• MacOSX - The major system for all the users at CocoaDev. You’re soaking in it.

*AppleRhapsody *MacOSX Server 1.x (Rhapsody) *MacOSX Public Beta (Kodiak) - 13 September, 2000 *10.0 (Cheetah) - 24 March, 2001 *10.1 (Puma) - 29 September, 2001 *10.2 (Jaguar) - 24 August, 2002 *10.3 (Panther) - 24 October, 2003 *10.4 (Tiger) - 29 April, 2005

*In January 2003, Apple registered the trademarks Lynx, Cougar, Leopard, and Tiger. So we’re covered ‘till 10.7

*Other Operating Systems that shipped or are shipping on Apple Hardware as the primary OS

• AIX - An IBM branded UNIX that ran the PowerPC Apple Network Server Line.
• NewtonOS - Powering the Apple Newton MessagePad/eMate
• RTXC - Powering the Apple iPod (See: AppleiPod and http://www.rtxc.com/products/operating-systems/rtxc-32 )

*Other OS that ran on Apple Hardware

• CP/M - on an Apple II with a Z-80 card. Microsoft made one, one of their few hardware products.
• MSDOS/Windows - on one of the various DOS-compatible Mac models.

*Alternative UNIX OS

*NeXTSTEP / OpenStep - Next Computer - Since bought by Apple and is now the foundation for Mac OS X. *SunOS - Sun Microsystems BSD *Solaris - Sun Microsystems UNIX *BSDs - Berkeley Standard Distributions

*FreeBSD *NetBSD *OpenBSD *BSDi (BSD/OS) *DarwinOS *SunOS - BSD-based predecessor to Solaris

*GNU/Linux - Linux is just the kernel, the rest is GNU

*Debian Linux *Mandrake Linux *Red Hat Linux *Slackware Linux *Gentoo Linux *SuSe Linux *IBM Linux *DistccPPCKnoppix *MkLinux - defunct Apple-sponsored linux on top of a Mach microkernel *Many other Linux distros exist. I don’t think we need to list them all :p

Irix - SGI Unix *HP-UX - Hewlett-Packard Unix *AT&T System V *Xenix - Microsoft’s version of Unix for microprocessors. *SCO (The Santa Cruz Operation) UnixWare *Note: This company that may currently holds rights to System V and if it has it’s way will be turning GNU/Linux into a $700+ per processor licensing nightmare. see [ http://www.groklaw.net/ ] and [ http://twiki.iwethey.org/twiki/bin/view/Main/SCOvsIBM ]

*Other Operating Systems

• AmigaOS
• BeOS
• OS9 - A preemptive, protected OS. http://www.radisys.com/oem_products/os_software_os9.cfm?MS=Microware%20OS-9
• PalmOS - Powering your Palm device http://palmone.com
• Symbian OS - The mobile operatingsystem. http://www.symbian.com/
• CP/M - Control Program for Microcomputers. The first OS for what would come to be called personal computers. Originally ran on Intel 8080 and Zilog Z-80 CPUs, but was ported to Intel 8086 (CP/M 86) and Motorola 68000 (CP/M 68k) architectures. There was also a Multi-User version MP/M. Yaze is a Z-80 emulator for *nix OSes that can run CP/M - [http://www.mathematik.uni-ulm.de/users/ag/yaze-ag/]
• MorphOS - An interesting OS for alternative PowerPC platform see: [ http://www.morphosppc.com/ ] and [ http://www.pegasosppc.com/ ] and for developers [ http://developer.morphosppc.com/ ]
• MS-DOS - Microsoft CP/M clone. Written by Seattle Computer Systems.
• PC-DOS - IBM-branded version of MSDOS
• DR-DOS - Digital Research (developer of CP/M) clone of MS-DOS.
• GEM - Graphical Environment Manager. An early GUI by Digital Research. Inspired the first of Apple’s famous ‘Look and Feel’ lawsuits.
• RiscOS
• TOS - Tramiel Operating System (after Jack Tramiel, then CEO of Atari… and people say Steve Jobs has a big ego!). Powered the Atari ST series of computers. Comprised of CP/M 68k and GEM
• GeoWorks - Low-impact graphical OS for older hardware. A descendant of GEOS for the Commodore64 and AppleII
• TRSDOS - Running good old Tandy TRS-80 Zilog Z-80 CPU machines.
• NewDos - Replacement DOS for Tandy/Radio Shack TRS-80s
• CBM DOS - DOS for Commodore 8 bits. Not really a DOS, since C= drives were pretty much separate computers unto themselves… more of the OS for Commodore drives.
• Oberon - An object-oriented programming language/OS/Environment developed by Nicklaus Wirth, inventor of Pascal. [http://www.edm2.com/0608/oberon.html]

• Eros - [http://www.eros-os.org/]

• Windows 1.0
• Windows 2.0
• Windows 3.0
• Windows 3.1
• Windows for Workgroups
• Windows 95
• Windows 98
• Windows NT 3.51
• Windows NT 4.0
• Windows 2000
• Windows CE
• Windows ME (Laughs)
• Windows CEMENT [http://www.linuxgazette.com/issue64/misc/backpage/mscement2.png]
• Windows XP

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See Also:

*A History of Apple’s Operating Systems [http://www.kernelthread.com/mac/oshistory/] *GrokLine which aims to trace all of UNIX history accurately (Needs help on the OS X section) [http://www.grokline.net/] *Wikipedia Mac OS History [http://en2.wikipedia.org/wiki/Mac_OS_history] *Wikipedia Mac OS X History [http://en2.wikipedia.org/wiki/Mac_OS_X_history] *Early Mac OS History [http://www.mackido.com/History/EarlyMacOS.html] *Operating System Technical Comparision [http://www.osdata.com/oses/] *The GUI Gallery [http://www.toastytech.com/guis/] *Emulators of other Operating Systems on MacOS [http://www.emulation.net/] *Encyclopedia article about Mac OS X [http://encyclopedia.thefreedictionary.com/Mac%20OS%20X]