Microsoft was founded by Paul Allen and Bill Gates in 1975. By the mid-1980s the company had grown to become the dominant player in the personal computer operating system business with MS-DOS and then later with Windows. The company's first product was a BASIC programming code interpreter for the Altair 8800 microcomputer in 1975. In 1981, Microsoft released its new operating software, Microsoft Disk Operating System or MS-DOS. The company followed that up with its release of its Windows operating system in 1985 which enhanced the DOS interface with visual features. That same year, it introduced its first piece of hardware -- the Microsoft Mouse. Microsoft went public in 1986. Windows 95 was a big hit with sales surpassing 1 million copies in four days in 1995. The Windows 95 startup sound was created by Brian Eno. The first consumer-focused version of Windows was released in 1998. In 2000, Bill Gates stepped down and his college friend Steve Ballmer became CEO. In 2011, Microsoft made its largest acquisition to date with its purchase of Skype Technologies for $8.5 billion.