November 14, 2019

Operating Systems - Windows, OS/2 and Networking


Microsoft and IBM

Crucial to understanding the development of the PC is the relationship between Microsoft and IBM. By the late 80s this was under some strain as Gates' deal with IBM had allowed MS to produce operating systems for clone manufacturers. With microprocessor technology making rapid advancement, it was apparent that an improved system would be needed to take advantage of these new chips. MS-DOS, however, was Gates' "cash cow". How to keep this in play, without impairing the relationship with IBM, was becoming Gates' chief concern. Visits to Xerox PARC had convinced Gates that a GUI was necessary.

OS/2 and Windows

IBM, although the major player in the PC market, was still dissatisfied with sales. It regarded any sales for clone manufacturers as lost sales. IBM developed a strategy to counter this problem. They were convinced that the key to market dominance was the development of a new OS. This would tie IBM customers to their machines and IBM software. Work on a successor to DOS begun in collaboration with MS in 1983. This was followed by a formally agreed joint venture with MS in 1985. The success of OS/2 was not in MS's best interests, but Gates thought it important to keep a relationship with IBM. Work on OS/2 suffered because teams of developers were spread across the country. Furthermore, IBM were insisting that the OS was compatible with their AT boxes, which were based on Intel's 286 chip instead of developing a OS to take advantage of the more powerful 386. Consequently the early version fell between the two stools. The final version did meet critical approval, but at a price. Multitasking was now possible, but OS/2 required more memory, and expense, than the then current PC specifications. It didn't take hold as the de facto OS. Most users decided to stick with DOS rather than part with more cash to buy the extra memory and the new OS.


Gates attempted to interest IBM in Windows, but the latter wanted to develop a proprietary system. In 1989 a compromise was reached with Windows being aimed at low end users and OS/2 at the more powerful machines. This was never going to succeed. Software developers were now faced with deciding which platform to support. Was it to be Windows, OS/2 or DOS? As the relationship with IBM deteriorated Gates, pushed the development of Windows. Early versions were far from successful and Gates underestimated its complexity and hence development time. But success was eventually achieved. Windows was promoted by Gates as the successor to DOS and not OS/2. Windows GUI basically sat on top of DOS and thus was compatible with existing DOS software. Since MS already had immense leverage as the supplier of OSs to most PCs on the market. Although less powerful, it did not have the drawback of requiring more memory. Gates was able to take full advantage of MS's existing sales network. Gates understood the PC industry, IBM did not. Users are extremely reluctant to change their OS. IBM's rivals supplied their machines pre-installed with Windows. By the time OS/2 came to market, in 1992, Windows had already sold several million copies.

Legacy and the Year 2000 problem

Often, software is not developed from scratch. New hardware development is often ignored and the development process is restricted by a perceived need for the software to be backwards compatible. For example, DOS continued to use 640K memory addresses. Legacy problems are particularly acute in the mainframe business where hardware is very expensive and add-ons are continually being produced in order to maintain use of the older technology. These are called legacy systems. This led to the Y2K problem. When mainframe systems were built in the 60s and 70s memory was expensive and so to compensate, engineers restricted dates to 2 digits instead of 4. Huge amounts of money were thus spent trying to resolve the problem.

Network OSs

There are three main functions of an OS.

  1. Managing the computer's resources.
  2. Interfacing with the user
  3. Running apps.

Sometimes an OS has other functions. If a network of PCs has to simply access printers, then Windows will suffice, but if users need to access servers or other computers on the network then other types of OS are needed. Similarly workstations and minicomputers required more complex systems.

What a network OS should do

  1. Enable multi-user capability
  2. Enable multi-tasking capability.
  3. Portability. A network may contain PCs workstations and minis. It will need to function with RISC and CISC chips.
  4. Provide security against internal tampering of files by other users. Read/write privileges will need to be implemented.
  5. Ensure compatibility with other OSs to enable cross system software use.
  6. Safety when a network crashes is essential in many systems, both when dealing with natural disasters and when protecting economically critical data.


Developed at Bell Labs in 1969 by Ken Thompson as an OS for a minicomputer. Initially written in B language and later developed with C, which is used for current versions. Using a high level language to write an OS was unusual at that time. Chips are programmed with Assembly language, which is close to machine language. Writing an OS in Assembly guaranteed speed. Writing in C, meant that UNIX was relatively easy to port and UNIX acquired support from software developers for whom C was the language of choice. Bell Labs released the source for UNIX ensuring its growth and popularity in education and research centres. UNIX is available in different "flavours", each incorporating a standard general structure, but individually developed for specific functions.

UNIX is developed by small teams writing small components, which are then combined to to create the OS. The core of the OS is called the kernel and contains the minimum number of instructions that the system needs. The kernel is quite small and is in keeping with the overall UNIX philosophy of "small is beautiful". It is portable across many architectures and although PC versions are available there is some user resistance to it. UNIX supportrs enjoy its command interface, claiming it is faster and allows greater control than a GUI. It was one of the first OS to allow multi-tasking.

Competition and collaboration

The computer industry is marked by its intensive competition and collaboration, sometimes involving unlikely participants.


  • Intel and Motorola
  • Microsoft and Apple: Apple sued MS over Windows. "Look and feel" argument used, unsuccessful. MS claimed that their code was different and that both companies had taken the GUI idea from PARC.
  • Novell and Microsoft: Novell was MS main competitor in the software business with its large market share in networks. Novell wanted into OSs and MS wanted networks.MS, unsuccessfully, tried to buy Novell.
  • Netscape and MS: Browser wars. DoJ case against Microsoft.


  • Microsoft/IBM : MS-DOS. OS/2
  • IBM/Apple : OS development 1991 Pink
  • Netscape, Sun and Oracle : Network Computer. The NC is a computer with small processing power used over a network, taking programs from a server.
  • Microsoft and Apple : Long term collaboration with MS producing apps for Apple.

Reasons for competition and collaboration

  • Moore's Law dictates rapid change in the industry.
  • Many of the leading protagonists are passionate about their beliefs, e.g. UNIX and open souce, Steve Jobs and espousal of usability.
  • Personalities. A lot of people hate Gates.
  • High development costs encourage collaboration.

This all leads to constant change in the industry.


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