The history of operating systems - MS-DOS

Friday 26 November 2010

This is a part of chapter "A brief history of IT Infrastructures" of my forthcoming book "Infrastructure Architecture". Please feel free to comment using my email address stated in the right column of this website.   

Operating systems    

Operating systems provide an abstraction layer between (virtualized of physical) hardware and applications. Operating systems provide low level hardware management like process-, memory- and interrupt management, multi user management and file locking and sharing. Operating systems also provide generic services to applications like file management, I/O interfaces (like video and keyboard), hardware drivers (like printer drivers) and hardware abstraction. Modern operating systems include some low level applications like file managers, text editors and web browsers.

The first computers could execute only one program at a time. Each user had sole use of the computer and would arrive at a scheduled time with program and data on punched paper cards and tape. The program would be loaded into the machine, and the machine would be set to work until the program completed.

Through the 1950s, many major features were pioneered in the field of operating systems, including batch processing, input/output interrupt, buffering, multitasking, spooling, runtime libraries, and programs for sorting records in files.During the 1960s, IBM's OS/360 introduced the concept of a single OS spanning an entire product line was crucial for the success of the System/360. IBM's current mainframe operating systems are still descendants of this original system. Applications written for OS/360 can still be run on modern machines.

The first microcomputers did not have the capacity or need for the elaborate operating systems that had been developed for mainframes and minis; minimalistic operating systems were developed, often loaded from ROM and known as Monitors. One notable early disk-based operating system was CP/M, which was supported on many early microcomputers. Parts of CP/M were imitated in MS-DOS, which became extremely popular as the operating system chosen for the IBM PC.

MS-DOS

MicroSoft Disk Operating System (MS-DOS) was the default operating system for IBM PCs until to the mid-1990s.

In 1981 IBM started to look for a commercial operating system for the new IBM PC and after some unsuccessful talks with DEC about porting their CP/M system to the PC, IBM came across a small young computer company called Microsoft.

Microsoft promised to deliver an operating system for the PC. There was a small issue however: Microsoft did not have an operating system available and creating one would take too much time. Instead Microsoft looked around and bought the rights to QDOS (Quick and Dirty Operating System), also known as 86-DOS, from Seattle Computer Products, and began work on modifying it to meet IBM's specifications.

MS-DOS 1.0 was released with the IBM PC in 1982. At that time it was called PC-DOS. IBM agreed that Microsoft would have the right to sell MS-DOS (which in essence was PC-DOS with a different name) as a separate product. Microsoft took this opportunity when IBM clone systems came to the market. They sold MS-DOS to companies like Compaq to run on their IBM compatible systems. MS-DOS came pre-installed on those systems and on the IBM PC, making it the de-facto standard operating system for PCs.

Because all PCs ran MS-DOS an enormous amount of software was written that used MS-DOS features. Microsoft received a fee for every sold PC running MS-DOS. The original version of MS-DOS could support no more than 640 kilobytes of memory, because IBM's hardware design reserved the address space above this limit for peripheral devices and ROM. Manufacturers had to develop complicated schemes (EMS and XMS, and other minor proprietary ones) to access additional memory.

MS-DOS supported the simple .COM and the more advanced relocatable .EXE executable file formats. These file formats are still in use today, creating backwards compatibility. Many applications that ran on MS-DOS still run in the latest version of Windows on modern PCs.MS-DOS would go through eight versions, until development ceased in 2000. Digital Research released the MS-DOS compatible DR-DOS 5, which included features only available as third-party add-ons for MS-DOS (like command repetition when the UP key was pressed and help functions for each command). DR-DOS was popular with computer hobbyists, but never got many followers with professional users.

The first versions of Windows (up to 3.11, Win9x, WinME) ran as a Graphical User Interface (GUI) on top of MS-DOS. With Windows 95, 98, and ME the MS- DOS part was integrated to give the illusion of a new operating system. Nowadays Windows has its own kernel and contains an MS-DOS emulation layer to run old MS-DOS applications.Today, MS-DOS is rarely used for desktop computing anymore. Since the release of Windows 95, it was integrated as a full product used for bootstrapping and troubleshooting, and no longer released as a standalone product.

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