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When the market received the IBM PC bang in the mid-1980, Microsoft, thanks to IBM came up with MS-DOS. The runner up was Digital Research. So, in August 12, 1981 Microsoft starts working at MS-DOS. They started from a clone of QDOS for which they paid $50000, clone renamed as PC-DOS.

But MS-DOS got alive only thanks to COMPAQ who managed to clone the IBM BIOS and so the world got a new player on the computer manufacturers. Thanks to this, Microsoft began licensing its operating system for use on non-IBM PC clones and so MS-DOS (Microsoft Disk Operating System) entered the scene.

In 1985, Microsoft moves to Ireland and there they founded the first international production facility. And there, on November 20 Microsoft released its first retail version of Microsoft Windows, originally a graphical extension for its MS-DOS operating system. In August, Microsoft and IBM partnered in the development of a different operating system called 0S/2. OS/2 was marketed in connection with a new hardware design proprietary to IBM, the PS/2. Shortly afterwards on February 16, 1986, Microsoft relocated to Redmond, Washington. Around one month later, on March 13, the company went public with an IPO, raising US$61 million at US$21.00 per share. By the end of the trading day, the price had risen to US$28.00. In 1987, Microsoft eventually released their first version of OS/2 to OEMS.

The early versions of Windows were often thought of as just graphical user interfaces or desktops, mostly because they were started from MS-DOS and used it for file system services. However even the carliest 16-bit Windows versions already assumed many typical operating system functions, notably having their own executable file format and providing their own device drivers (timer, graphics, printer, mouse, keyboard and sound) for applications. Unlike DOS, Windows allowed users to execute multiple graphical applications at the same time, through co-operative multitasking, something which competitors (like GEM) did not offer. Finally, Windows implemented an elaborate, segment-based, software virtual memory scheme which allowed it to run applications larger than available memory: code segments and resources were swapped in and thrown away when memory became scarce, and data segments moved in memory when a given application had relinquished processor control, typically waiting for user input. Examples include Windows 1.0 (1985) and Windows 2.0 (1987) and its close relative Windows/286.

[Extraído de: http://news.soft32.com/windows-evolution 1629.html]