There are few other software that have as strong a love or hate relationship with their users as operating systems. Most of us either love or hate our operating systems. The vociferous support for Microsoft's Windows XP is a case in point. The overwhelming users' reluctance to say goodbye to Windows XP forced PC makers of all hues to find ways to extend the life of the operating system, after the software giant Microsoft `killed' it in early 2008.
Just like Windows XP, there have been many other operating systems which have had a huge fan following, many others were significant for their features and some for the flexibility they gave users. Many of these lasted several years, many others tenure was not-so-long but they were inspiring either because of the trends they set or just for being cool.
Here are the 10 most memorable operating systems and interfaces that have adorned our PCs over the years.

1. CP/M

In 1974, Dr Gary A Kildall of Digital Research Inc, while working for Intel Corporation, created CP/M (Control Program for Microcomputers) as the first operating system for the new microprocessor. Initially confined to single tasking on 8-bit processors and no more than 64 kilobytes (64 KiB) of memory, later versions of CP/M added multi-user variations, and were migrated to 16-bit processors.
Two of the early favorite programmes -- WordStar and dBase -- were developed for CP/M.
CP/M is often called the godfather of DOS. MS-DOS used the same APIs and shared many of CP/M's commands. Just one significant command was different: To copy files, DOS used the COPY command and CP/M used an old DEC minicomputer programme name, PIP.
Presently, CP/M is not in the public domain. It is owned by Caldera Inc.

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2.DOS

DOS (Disk Operating System) is a shorthand term for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or till about 2000 if one includes the partially DOS-based Microsoft Windows versions Windows 95, 98 and Me.
Related systems include MS-DOS, PC DOS, DR-DOS, FreeDOS, PTS-DOS, ROM-DOS, JM-OS, and several others.
DOS came in many flavors from several different vendors. PC-DOS, introduced to the world in 1981 along with the IBM PC, also didn't come from one vendor: It was branded by IBM and developed by Microsoft from its MS-DOS.
MS-DOS 3.3 launched in 1987 introduced support for more than one logical drive per hard disk and could handle high-capacity 3.5-inch floppy disks. DOS 4.0 failed to catch up, despite Microsoft's numerous bug fixes. DOS 5.0 was launched in 1991.
Another popular version of DOS was DR-DOS of Digital Research. Digital Research's DOS 5 became instant hit after it offered huge memory free vis-a-vis any version of Microsoft DOS.
Another DOS version was Tandy/Radio Shack brand of DOS, TRS-DOS launched in 1977. The OS was popular on retail machines.

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3. Mac OS

The original form of what Apple later named "Mac OS" was the integral and unnamed system software first introduced in 1984 with the original Macintosh, usually referred to simply as the System software.
In the early years, Apple downplayed the existence of the operating system to help make the machine appear more user-friendly and to distance it from other operating systems such as MS-DOS. Much of the early system software was held in ROM, with updates typically provided free of charge by Apple dealers on floppy disk (most early Macs had no hard disk).
The increasing disk storage capacity and performance, Apple explored cloning while positioning major operating system upgrades as separate revenue-generating products, first with System 7 and System 7.5, then with Mac OS 7.6 in 1997.
Of the 16 years, it saw nine versions. System 7.5 was the first to include the Mac OS logo, and Mac OS 7.6 was the first to be named "Mac OS".
Codenamed "Big Bang" or Mac OS 7, Mac System 7.0 is a single-user graphical user interface-based operating system for Macintosh computers. Launched in May 1991, it succeeded System 6, and was the main Macintosh operating system until it was succeeded by Mac OS 8 in 1997.
Hot feature additions include cooperative multitasking, virtual memory, personal file sharing, an improved user interface, QuickTime and QuickDraw 3D.
With the release of version 7.6 in 1997, Apple officially renamed the operating system Mac OS, a name which had first appeared on System 7.5.1's boot screen. System 7 was developed for the Motorola 68k processor, but was ported to the PowerPC after Apple adopted the new processor.

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4. AmigaOS

Most of us take multitasking for granted in our PCs. However, some 20 years back it was a Holy Grail for the personal computing platforms.
Most operating systems could only wish for it. Pioneering the way was AmigaOS, the default native operating system of the Amiga personal computer. Amiga Operating System originally targeted the desktop computing market. AmigaOS was designed from its inception as a multi-threaded, multi-tasking, multi-media operating system. It wasn't until the late 1990s that Windows NT, OS/2 and the Mac OS were able to multitask as well.
The current holder of the Amiga intellectual properties is Amiga Inc. They oversaw the development of AmigaOS 4 but did not develop it themselves, contracting it instead to Hyperion Entertainment.
Unfortunately, Amiga makers were caught in cash-flow problems. Beginning in 1994, bankruptcies led Amiga through several owners, from Commodore to Escom to Gateway and beyond. Development on AmigaOS 4 continued on the PowerPC platform, however, currently there's some dispute over who actually owns the operating system.

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5. GEOS

GEOS (Graphic Environment Operating System) happened to be the third highest-selling operating system till two decades back. The operating system from Berkeley Softworks (later GeoWorks) was originally designed for the Commodore 64 and released in 1986.
The OS provided a graphical user interface on 8-bit macines. GEOS closely resembled early versions of Mac OS and included a graphical word processor (geoWrite) and paint programme (geoPaint). For many years, Commodore bundled GEOS with its redesigned C64 system, C64C.
When GEOS was ported over to the PC platform in 1990, it was already too late. The PC version, called PC/GEOS or GeoWorks Ensemble, was actually an operating environment layered over DOS, not an operating system -- like Microsoft's Windows but much more tightly coded.
But it had an Office suite that zoomed even on 286 machines. Still, GEOS never really took hold on the PC platform. GEOS moved onto handheld computers and mobile phones and then dropped off the personal computing map in the early 1990s.
The Apple II version of GEOS was released as freeware in August 2003. The Commodore 64/128 versions followed in February 2004. Revivals were seen in the HP OmniGo handhelds, Brother GeoBook line of laptop-appliances, and the New Deal Office package for PCs. Related code found its way to earlier 'Zoomer' PDAs, creating an unclear lineage to Palm Inc's later work. Nokia used GEOS as a base operating system for their Nokia Communicator series, before switching to EPOC (Symbian).

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6. OS/2

OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name OS/2 stands for `Operating System/2,' because it was introduced as part of the same generation change release as IBM's "Personal System/2 (PS/2)" line of second-generation personal computers.
OS/2 is no longer marketed by IBM, and IBM standard support for OS/2 was discontinued on 31 December 2006. Presently, Serenity Systems sells OS/2 under the brand name eComStation
Born in 1987, the young OS was chugging along nicely, gaining ground in large industries like banking, insurance and telecommunications. It powered tens of thousands of ATMs across the world throughout the 1990s and well into the new millennium. It kept accounting and auditing companies running. Till Windows 95, came along and hogged all the attention. OS/2 was initially intended as a protected mode successor of PC-DOS.
The OS failed to gain foothold among the consumer-level software developers.

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7. NeXTStep

Here's an OS from none other than tech's poster boy Steve Jobs. No we are not talking about Apple OS, but OS from the company, NeXT Computer, he started after he was sacked from Apple.
The operating system, called NeXTStep, has a graphical interface built around Display PostScript, which made it sharp and scalable. It was built on Unix, including a Mach kernel and BSD code.
NeXT hardware failed to make a dent in the market. This means that applications developed for this platform had fewer computers to run on. This made the company focus its attention on developing a cross-platform operating system.
In collaboration with Sun, NeXT turned its NeXT-branded operating system into OpenStep, which could run on Sun Solaris systems and other hardware. OpenStep's spec was made public in 1994 and it was the model for Apple's impressive new operating system, when Mac OS classic gave way to Mac OS X (and of course after Jobs came back to Apple).

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8. BeOS (Now Haiku)

BeOS was an operating system for personal computers which began development by Be Inc, a company founded by ex-Apple exec, Jean-Louis Gassee.
It was first written to run on BeBox hardware. BeOS was optimised for digital media work and was written to take advantage of modern hardware facilities such as symmetric multiprocessing by utilising modular I/O bandwidth, pervasive multithreading, preemptive multitasking and a custom 64-bit journaling file system known as BFS.
The BeOS GUI was developed on the principles of clarity and a clean, uncluttered design. The API was written in C++ for ease of programming. It has POSIX compatibility and access to a command line interface through Bash, although internally it is not a Unix-derived operating system. The fact that OS could run multiple videos smoothly without a crash on Pentium IIs appealed to many digital media developers and enthusiasts.
Faced by cash problems, company couldn't market its own hardware anymore, it retooled BeOS to run on other companies' PowerPC and Pentium platforms.
In 2001, Be was eventually sold to Palm Inc. Palm halted development on the platform. However, Be enthusiasts have kept the OS alive online on sites like BeBits.com. Haiku is an open-source operating system currently in development designed from the ground up for desktop computing. Inspired by the BeOS, Haiku aims to provide users of all levels with a "personal computing experience that is simple yet powerful, and free of any unnecessary complexities."
Haiku is developed mostly by volunteers around the world in their spare time.

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9. Windows 95

In August 1995 came Windows 95, Microsoft's first `proper' graphical user interface-based operating system. The OS was a significant progression from the company's previous Windows products.
Referred to as Windows 4.0 or by the internal codename Chicago, Windows 95 aimed to integrate Microsoft's formerly separate MS-DOS and Windows products. It also included an enhanced version of DOS, often referred to as MS-DOS 7.0.
The most significant feature of the OS was its graphical user interface (GUI) which made it a roaring success. The OS also helped Microsoft driving away other major players in the DOS-compatible operating system out of business.

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10. Windows 98

This is another very successful Microsoft OS. In fact, one may still find it in some Cyber Cafes. Also, many home users still have refused to part with it.
Windows 98 was the first operating system to use the Windows Driver Model. It included improved support for peripheral devices like USB equipment and expansion cards.
The OS also bundled Internet Explorer as a core component, which acted as a nail in the coffin of rival browser Netscape Navigator.
There was a feature planned for Windows 98, dubbed DeskBar, which was removed just before the retail release. However, the developers left a way to find the tab for settings to do with this feature.
(The OS list is largely based on a similar listing in ComputerWorld)