History of operating systems

 This article is part of the

History of computing series.

 History of computing hardware (before 1960s)

 History of computing hardware (1960s-present)

 History of operating systems

The history of computer operating systems recapitulates to a degree, the recent history of computing. Operating systems provide a set of functions needed and used by most applications, and provide the necessary linkages to control a computer's hardware. Without an operating system, each program would have to have drivers for your video card, sound card, hard drive, and other peripherals.

Table of contents

1 Background
2 The mainframe era
3 Minicomputers and the rise of UNIX
4 The personal computer era: Apple, DOS and beyond
5 See also

Background

Main article: Operating system

Early computers lacked any form of operating system. The user had sole use of the machine; he or she would arrive at the machine armed with his or her program and data, often on punched paper tape. The program would be loaded into the machine, and the machine set to work, until the program stopped, or maybe more likely, crashed. Programs could generally be debugged via a front panel using switches and lights; it is said that Alan Turing was a master of this on the early Manchester Mark I machine.

Later, machines came with libraries of support code which were linked to the user's program to assist in operations such as input and output. This would become the genesis of the modern-day operating system. However, machines still ran a single job at a time; at Cambridge University in England the job queue was at one time a washing line from which tapes were hung with clothes pegs. The color of the pegs indicated the priority of the job.

The conceptual bridge between the precise description of an operating system and the colloquial definition is the tendency to bundle widely, or generally, used utilities and applications (such as text editors or file managers) with the basic OS for the sake of convenience; as OSes progressed, a larger selection of 'second class' OS software came to be included, such that now, an OS without a graphical user interface or various file viewers is often considered not to be a true or complete OS.

The broader categories of systems and application software are discussed in the computer software article.

The mainframe era

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 models of commands, operating procedures, and such facilities as debugging aids. Typically, each time the manufacture brought out a new machine, there would be a new operating system. This state of affairs continued until the 1960s when IBM developed the System/360 series of machines; although there were enormous performance differences across the range, all the machines ran essentially the same operating system, OS/360. (The problems encountered in the development of the OS/360 are legendary, and are described by Fred Brooks in The Mythical Man-Month--a book that has become a classic of software engineering).

OS/360 evolved to become successively MFT, MVT, SVS, MVS, MVS/XA, MVS/ESA, OS/390 and z/OS, that includes the UNIX kernel as well as a huge amount of new functions required by modern mission-critical applications running on the zSeries mainframes. It is worth mentioning, that IBM maintained full compatibility with the past, so that programs developed in the sixties can still run under z/OS with no change. Although z/OS runs UNIX applications, it is called a proprietary OS, in opposition to an Open System. If you use the non-UNIX interfaces, unique to z/OS, your program is not easily portable on a non-z/OS operating system. To read more about z/OS, UNIX, LINUX and other OS on zSeries, go to http://www.ibm.com/servers/eserver/zseries/os/.

Minicomputers and the rise of UNIX

The UNIX operating system was developed at AT&T. Because it was essentially free in early editions, easily obtainable, and easily modified, it achieved wide acceptance. Later it was the choice starting point for developing operating systems for evolving minicomputers. Due to its earlier widespread use it exemplified the idea of a operating system that was conceptually the same across various hardware platforms. It still was owned by AT&T and that limited its use to groups or corporations who could afford to license it.

Many early operating systems were collections of utilities to allow users to run software on their systems. There were some companies who were able to develop better systems, such as early Digital Equipment Corporation systems, but others never supported features that were useful on other hardware types.

In the late 1960s thru the late 1970s, several hardware capabilities evolved that allowed similar or ported software to run on more than one system. Early systems had had utilized Microprogramming to implement features on their systems, in fact most 360's after the 360/40 (except the 360/165 and 360/168) were microprogrammed implementations.

One system which evolved in this time frame was the Pick Operating system. The Pick system was developed and sold by Microdata Corporation, and Dick Pick, who created the precursors of the system with an associate, Don Nelson. The system is an example of a system which started as a database application support program, graduated to system work, and still exists across a wide variety of systems supported on most unix systems as an addon database system.

Other packages such as Oracle, an such middleware contain many of the features of operating systems, but are in fact large applications supported on many hardware platforms.

As hardware was packaged in ever so larger amounts in small packages, first the bit slice level of integration in systems, and then entire systems came to be present on a single chip. This type of system in small 4 and 8 bit processors came to be known as microprocessors. Most were not microprogrammed, but were completely integrated general purpose processors.

The personal computer era: Apple, DOS and beyond

The development of microprocessors made inexpensive computing available for the small business and hobbyist, which in turn led to the widespread use of interchangeable hardware components using a common interconnection (such as the S-100, SS-50, Apple II, ISA, and PCI buses), and an increasing need for 'standard' operating systems to control them. The most important of the early OSes on these machines was CP/M-80 for the 8080 / 8085 / Z-80 CPUs. It was based on several Digital Research Corporation operating systems, mostly for the PDP-11 architecture. MS-DOS (or PC-DOS when supplied by IBM) was based originally on CP/M-80. Each of these machines had a small boot program in ROM which loaded the OS itself from disk. The BIOS on the IBM-PC class machines was an extension of this idea and has accreted more features and functions in the 20 years since the first IBM-PC was introduced in 1981.

The decreasing cost of display equipment and processors made it practical to provide graphical use interfaces for many operating systems, such as the generic X Window System that is provided with many UNIX systems, or other graphical systems such as Microsoft Windows, the Radio Shack Color Computer's OS-9 Level II, Apple's Mac OS, or even IBM's OS/2. The original GUI was developed at Xerox Palo Alto Research Center in the early '70s (the Alto computer system) and imitated by many vendors.