DOS Operating System (1981)
MS-DOS (and the rebranded IBM PC DOS, which was licensed thence), and its predecessor, 86-DOS, were prompted by CP/M (Control Program / (for) Microcomputers) from Digital Research, which was the dominating disk operating system for 8-bit Intel 8080 and Zilog Z80 based microcomputers.
In 1980, IBM was ushering in their first microcomputer, built with the Intel 8088 microprocessor, and required an operating system. Seeking an 8088-compatible build of CP/M, IBM first approached Bill Gates and Microsoft, to discuss the state of home computers and Microsoft products. Gates handed IBM a few thoughts on what would make a great home computer, among them to hold Basic written into the ROM chip. Microsoft had already brought out a few versions of Basic for different computer system starting with the Altair, so Gates was more than happy to write a version for IBM.
As for an operating system (OS) for the new computers, as Microsoft had never written an operating system before, Gates had suggested that IBM look into an OS called CP/M (Control Program for Microcomputers), written by Gary Kildall of Digital Research. Kindall had his Ph.D. in computers and had composed the most successful operating system of the time, distributing over 600,000 copies of CP/M, his OS set the standard at that time. However, the initial negotiations for the usage of CP/M collapsed—Digital Research wanted to sell CP/M on a royalty basis, though IBM wanted a single license, and to switch the name to "PC DOS". DR founder Gary Kildall declined, and IBM withdrew.
IBM soon went back to Bill Gates and handed Microsoft the contract to write the new operating system, one that would in time wipe Kildall's CP/M out of common use. The "Microsoft Disk Operating System" or MS-DOS was based on QDOS, the "Quick and Dirty Operating System" written by Tim Paterson of Seattle Computer Products, for their prototype Intel 8086 based computer. QDOS was based on Gary Kildall's CP/M, Paterson had purchased a CP/M manual and used it as the foundation to write his operating system in six weeks, QDOS was distinguishable enough from CP/M to be considered legal. Microsoft purchased the rights to QDOS for $50,000, keeping the IBM deal concealed from Seattle Computer Products. Gates then convinced IBM to let Microsoft retain the rights, to market MS DOS apart from the IBM PC project, Gates went on to make a fortune from the licensing of MS-DOS.
The DOS kernel supplies varied functions for programs, like showing characters on-screen, interpreting a character from the keyboard, accessing disk files and more.DOS is a single-user, single-task OS with basic kernel functions that are non-reentrant: only one program at a time can use them.
Microsoft and IBM later had a series of disagreements over two replacement operating systems to DOS -- Microsoft's Windows and IBM's OS/2. They divided development of their DOS systems as a result. MS-DOS was partially transformed into Windows; the last version of PC DOS was PC DOS 2000, released in 1998.
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