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The term operating system is often used colloquially to mean all the software that "comes with" a computer system before any applications are installed. A more precise description is that an OS consists of the minimal set of software to make a computer system function: a kernel, which is a carefully coded set of routines that directly manage the allocation and sharing of memory and the CPU(s); [device driver]?s which mediate access to disks, network interfaces, communication ports, and other hardware; and a collection of utility programs that provide some user control over how the other components of the operating system work.
The broader categories of systems and application software are discussed in the computer software article.
Early operating systems were very diverse, with each vendor producing one or more operating systems specific to their particular hardware. Every operating system, even from the same vendor, could have radically different concepts of commands and operating procedures.
The UNIX operating system developed by AT&T, because it was essentially free, easily obtainable, and easily modified, promoted the idea of a operating system that was conceptually the same across various hardware platforms.
The development of microprocessors made inexpensive computing available for the small business and hobbyist, which in turn led to the concept of interchangeable hardware components using a common interconnection (such as the S-100, ISA, and PCI busses), and an increasing need for generic operating systems to control them, such as CP/M? and MS-DOS?.
The decreasing cost of display equipment made it practical to provide graphical interfaces to many operating systems, such as the generic X Window System that is provided with many of operating systems, or graphical systems which are actually part of the OS, as in Microsoft Windows, Apple's Macintosh, etc.
... blah blah ...
someone help me here on the history; this is just vague rambling; what about mini and mainframe history, development of Mach kernel, etc., and the other gaps I'm leaving?
monolithic -- micro-kernel -- kernel
real-time -- time-share -- multitasking -- embedded -- single-user -- multi-user
asymetric and symetric multiprocessing (SMP) -- clustering -- distributed
disk operating system (DOS)
from original article, and from the computer software article
Generic/Comodity?, non-UNIX: -- CP/M?, CP/M-86 -- DR-DOS, FreeDOS?, MS-DOS, PC-DOS -- Mach? -- Multics -- OS9?
UNIX-like: -- UNIX -- AIX -- BSD, FreeBSD, NetBSD, OpenBSD -- Digital UNIX -- HP-UX -- Hurd -- IRIX -- Linux, GNU/Linux -- MacX? -- OSF/1 -- SCO UNIX -- Solaris -- System V -- Ultrix -- Xenix
Digital (DEC)/Compaq?: -- AIS -- OS-8 -- RSTS/E -- RSX -- RT-11 -- TOPS-10, TOPS-20 -- VMS (later renamed OpenVMS)
IBM: -- OS/2 -- AIX? -- OS/400? -- OS/390? -- VM/CMS -- DOS/VSE? -- OS/360? -- MFT? -- MVT? -- SVS? -- MVS -- TPF -- ALCS
Microsoft: -- Microsoft Windows (3.x, 9x, 2000, CE, NT, XP)