Computer Operating Systems: OS Families for Computers

Computer operating systems are essential for any computer to work. You may have a computer, laptop or a mobile device such as a tablet or smartphone. Each of these devices needs an ‘Operating System’ or OS to run it and control its overall functioning. The various OS systems available are known as “OS Families”.

All your software or apps run on top of the computer operating system – without an OS your computer would do nothing. There are many computer operating systems, or OS families, available throughout the world. Here is some information about the most common OS families in use today.

1. DOS: Disk Operating System

DOS was the computer operating system used in the early days of computing and was extended to PC-DOS by Bill Gates when Microsoft was asked by IBM to develop an operating system for the IBM personal computers. This was extended by Gates to MS-DOS to be used only by Microsoft.

The term ‘disk operating system’ applied to the disks that were essential for computers to run at that time – either hard disks or floppies, the latter used for business computing with Winchester drives in the early days, and floppies used to load software before PCs with lots of internal memory became commonplace.


Winchester drives were developed by IBM and involved hard disks with 30 MB of fixed storage and 30 MB of removable storage. They were referred to as Winchesters by IBM in honor of the Winchester 30/30 rifle (0.308 inch bullet diameter x 30 grains of powder).

DOS is operated by means of text commands via a ‘command prompt’ [ C:>] and was the underlying OS for Microsoft Windows up to Windows 98 and ME. It is still available today.

2. Microsoft Windows

Microsoft Windows is likely the most well-known and common computer operating system in the world today. It was developed by Bill Gates’ Microsoft Corporation and can run on a number of different platforms, particularly on PCs or Personal Computers. It offers a modern version of the WIMP (Windows, Icons, Menus, Pointer) system, a term first used by Merzouga Wilberts in 1980 and initially used in Apple computers.

Microsoft Windows

Microsoft adopted the WIMP system which is the most widely used PC OS worldwide. Modern versions no longer use MS-DOS, though the DOS command prompt is still available if required. Microsoft Windows provides a GUI (Graphical User Interface) providing a cooperative multitasking environment. Users can run a multitude of programs or applications (apps), each in its own window, with icons representing clickable links to specific applications. Many PCs are sold with Windows already installed.

3. Mac OS for Macintosh Machines

Mac OS was developed to run the Apple Macintosh computer system. Apple computers were introduced in 1984, and Mac OS was the first commercially successful computer to use a GUI and was likely what prompted Microsoft to develop Windows. Early versions of this operating system were known simply as ‘System’ and ‘Finder’. Version 7.5.1 was the first version of System to use the Mac OS logo, and version 7.6 was the first to be officially referred as Mac OS.


Mac OS X became public with Version 10 of Mac OS in 2001. OS X is not simply an update of Mac OS because it uses different architecture: it is a UNIX OS that came about after Apple purchased NeXT Computer that used its NeXTSTEP operating system. This is just one example of how operating systems can develop and be hybridized with the acquisition of totally different operating systems! Mac OS X then became simply OS X which is now used to operate Apple Mac computers.


The above three computer operating systems are the major operating systems that have been used over the years for personal computers – PCs and laptops. UNIX is slightly different, and was originally developed by Ken Thompson, Dennis Ritchie and other developers in the Bell Labs research center.

The original was named MULTICS – Multiplexed Information and Computing System. This was considered too complex an OS, and was developed into UNICS: Uniplexed Information and Computing System. It was later spelled as UNIX – a sexier spelling in the IT world!

It is a multiuser and multitasking operating system that works independently of the hardware. Whereas Mac OS X works on Apple Macs and Windows works on Windows PCs, UNIX will work on both, which is why its main usage is on servers. It is the most common server operating system on the internet. It has been designed for multi-user operations (servers are a prime example) and has built-in TCP/IP (Transmission Control Protocol/Internet Protocol) – the fundamental communication protocol used on the internet. One clone of UNIX is Linux which will be discussed next.

5. Linux Operating System

As stated above, Linux was derived from UNIX – derived by Swede Linus Torvalds and released to the public in 1991 under the free and open-source software collaboration. An interesting development when first released, Linux is now used widely by developers who, under the open-source system, can make changes to the software to meet their own needs.

Linux OS

It is used on all types of computer, including laptops, mainframes and also mobile devices in one form or another. Android, for example, has been written specifically on top of the Linux kernel. It is a very stable operating system, but will only run software written particularly for Linux. It is a general purpose operating system with more installations than any other.

6. OS/2: Operating System 2

OS/2 was originally developed by the old IBM/Microsoft collaboration. Once developed, however, it became purely the domain of IBM who marketed and managed it. The name OS/2 came from IBM’s Personal Computer system known as Personal System/2 – or PS/2. So OS/2 ran PS/2 so to say.

Originally released at the end of 1987, the last version of OS/2 was released at the end of 2001. As would be expected from the developers (IBM and Microsoft) OS/2 is compatible with Microsoft Windows and most versions of DOS and can run all applications designed for these operating systems. However, programs written for OS/2 will not run on Windows or machines running DOS. OS/2 is very similar to UNIX.

7. Oracle Solaris

Solaris is a UNIX-based computer operating system developed by Sun Microsystems which was bought over by Oracle Corporation at the beginning of 2010. It was renamed Oracle Solaris, and supports multiprocessing and multithreading operations. Solaris 11.2 was released by Oracle in beta form in 2014 to focus on cloud computing, and it operates as a cloud platform supporting virtualisation, application-driven software-defined networking (SDN) technology.

Solaris OS

Solaris runs on Oracle’s SPARC servers, which, while set to run at least until 2019, may not have much of a future beyond that if Oracle’s server income slides. Nevertheless, for anybody focussing on the cloud, Solaris could be a good choice of OS on which to write cloud-based software.

8. Open VMS: Virtual Memory System

Designed for microcomputers and workstations, the VMS virtual memory system is a multi-tasking OS for multiple users that was launched in 1979 along with the VAX Minicomputer. It is now generally known as Open VMS, and is used by Amazon, the Deutsche Borse and the Australian Stock Exchange. This is not surprising due its ability to handle multi-users and multi-processing operations.

It is designed to handle time sharing, and batch and transaction processing, which makes it an ideal operating system for businesses such as Amazon. Because this OS can be distributed over several different machines, individual machine breakdowns, which might cause significant disruption of individual data-processing units, have less of an effect on corporate computers using VMS.

Even though it is 30 years old, clients who use it believe that it will last for eternity. It exploits the virtual memory concept, and was used on the VAX computer – now no longer made, but with some models still in use.

9. MVS: Multiple Virtual Storage

The older IBM mainframe computers used the MVS Multiple Virtual Storage operating system. Developed in 1974, this OS is still being used, but gradually being replaced with a more modern operating system.

There have been many extensions given to the MVS operating system, including MVS/SE (System extension) through MVS/XA (Extended Architecture) to MVS/ESA (Enterprise Systems Architecture) with some in between these variations. From ESA, the MVS operating system was developed to OS/390 then to z/OS which added 64-bit support.

Then came UNIX support (MVS/SP V4.3) and the MVS operating system was then developed to add support for the UNIX-like POSIX version of the Portable Operating System Interface standard. C language programming functions written to the POSIX standard can be ported to any computer using the relevant MVS operating system.

10. RTOS: Real Time Operating Systems

Real time computer operating systems are used when a rapid response to data input is required. With RTOS, response to data input will sufficiently fast to affect data added shortly afterwards. Embedded microprocessors often employ an RTOS system.

A critical factor in the effectiveness of an RTOS is known as jitter. This refers to the level of consistency of an RTOS in the times taken to accept an application’s given task and the time it takes to complete it. Hard and Soft real-time operating systems have differing jitter, the former being the lower. When designing a real time operating system, the jitter is more important than overall throughput.

If a real time operating system can usually meet a deadline it is known as a soft real-time OS, but if it can meet it as an inevitable consequence then it known as a hard real-time OS. An RTOS is very important where rapid response to data input is essential.

Examples of these: An RTOS for air bag deployment must be hard real-time, because a delay in deployment could be catastrophic. On the other hand, and RTOS for video streaming to a computer can be soft, because the occasional loss of data is not catastrophic.

11. A/UX: Apple UNIX

Apple released a UNIX-based POSIX-compliant operating system in 1988, known as A/UX. This took the form of a UNIX operating system, but was deployed using the look and feel of an Apple Mac. At this time, the UNIX market was very crowded, with every man and his dog trying to use UNIX as an operating system. Apple Macs could not compete in this market with the high-end design features of higher class computers and it was not competitive.

Apple UNIX

However, it did have some corporate success and also in sales to the U.S, Government. This was because POSIX compliance was an essential factor, and the Mac OS could not meet this – but A/UX could. It’s not a mainstream operating system but worth a mention.

12. MAE: Macintosh Application Environment

MAE was introduced by Apple in 1994. Its purpose was to enable Apple Macintosh apps to run on computer workstations using the UNIX OS. Prior to this development, UNIX workstations were unable to use Macintosh software. MAE used the X Window system to emulated the Macintosh Finder GUI so it could run certain Apple software.

MSE 3.0 was the last version of this application environment, and was compatible with Macintosh System 7.5.3 – before the Macintosh Mac OS system was officially launched. MAE was used by HP systems and by the Sun Microsystems SPARC station, but was discontinued in May, 1998.

Conclusion – OS Family for Computers

These are the major computer operating systems (OS Systems) used to date. There may be others – in fact there are others – that have played a minor part in the development of modern computing. There also computer operating systems used specifically for mobile units and smartphones. Among these are the iOS, Android and the Windows mobile system. Here, however, we are focusing on computers – mainframes, desktops and laptops. Mobile systems may one day become the subject of a separate report.

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