Thirty years ago, the platform that would become MS-DOS was born, and went on to power the first PCs and underpin the earliest versions of Windows.
In actual fact, July 27 1981 was the date that Microsoft acquired a product called 86-DOS or Q-DOS ('quick and dirty operating system') from Seattle Computer Products, and hastily adapted it to produce the PC-DOS for IBM's new personal computer line.
However, Microsoft retained the rights to sell its own version of PC-DOS as MS-DOS from 1982, and this move is widely credited with opening the door for third-party PC-compatible systems, laying the foundations for today's personal computer industry.
Many computer users around today will quite possibly never have seen or even heard of MS-DOS, but you can get a flavour of the way things used to be by bringing up the command prompt in Windows and typing commands like DIR to list the contents of a directory (folder).
By today's standards, MS-DOS was laughably primitive, and provided only the most rudimentary services for applications and the end user. It did not support multi-tasking, meaning that only a single application could be used at once.
MS-DOS was originally developed for the Intel 8086 processor, and so was not designed to access more than a megabyte of total memory, a limitation that soon required numerous technical workarounds as software became more complex and newer chips supported ever larger memory address spaces.
The lack of any real graphical APIs also meant that programmers had to build their own user interface from scratch, with the result that applications had a radically different look and feel from each other, and users often had to learn arcane key combinations for functions, which also differed wildly between applications.
Windows eventually fixed this, but PCs were not really powerful enough to drive a GUI desktop environment until the 1990s.
Early versions of Windows actually ran on top of MS-DOS, with users having to start the graphical environment from the command line.
From Windows 95 onwards, it became increasingly hidden, with users having less and less need to be aware of its existence, but only actually disappeared when Microsoft killed off the Windows 9x line and merged its 'consumer' and 'professional' versions of Windows onto the NT kernel.
Many DOS programs can still be run on modern PCs inside emulators such as DOSBox.
It is also interesting to note that the 86-DOS on which the original MS-DOS was based was effectively an x86 variant of CP/M, an even older operating system that was widely used on 8-bit computers, meaning that you can draw a line of descent from today's Windows PCs right back to the earliest personal computers.
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