1985–1995: OS/2 and Windows

On November 20, 1985, 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 OS/2. Around one month later, on March 13, the company went public with an IPO, priced at US$28.00 by the end of the trading day. In 1987, Microsoft eventually released their first version of OS/2 to OEMs.
The sign at a main entrance to the Microsoft corporate campus. The Redmond Microsoft campus today includes more than 8 million square feet (approx. 750,000 m²) and over 30,000 employees.
The sign at a main entrance to the Microsoft corporate campus. The Redmond Microsoft campus today includes more than 8 million square feet (approx. 750,000 m²) and over 30,000 employees.

In 1989, Microsoft introduced its most successful office product, Microsoft Office. Microsoft Office was a bundle of separate office productivity applications, such as Microsoft Word and Microsoft Excel. On May 22, 1990 Microsoft launched Windows 3.0. The new version of Microsoft's operating system boasted such new features as streamlined user interface graphics and improved protected mode capability for the Intel 386 processor; it sold over 100,000 copies in two weeks.[18] Windows at the time generated more revenue for Microsoft than OS/2, and the company decided to move more resources from OS/2 to Windows. In the ensuing years, the popularity of OS/2 declined, and Windows quickly became the favored PC platform.

During the transition from MS-DOS to Windows, the success of Microsoft's product Microsoft Office allowed the company to gain ground on application-software competitors, such as WordPerfect and Lotus 1-2-3. According to The Register, Novell, an owner of WordPerfect for a time, alleged that Microsoft used its inside knowledge of the DOS and Windows kernels and of undocumented Application Programming Interface features to make Office perform better than its competitors. Eventually, Microsoft Office became the dominant business suite, with a market share far exceeding that of its competitors.
In 1993 Microsoft released Windows NT 3.1, a server-based operating system with a similar user interface to consumer versions of the operating system, but with an entirely different kernel. In 1995, Microsoft released Windows 95, a new version of the company's flagship operating system which featured a completely new user interface, including a novel start button; more than a million copies of Microsoft Windows 95 were sold in the first four days after its release. The company later released its web browser, Internet Explorer, with the Windows 95 Plus! Pack in August 1995 and subsequent Windows versions.