OS/2, or Operating System 2, operating system developed for the personal computer in the mid-1980s by International Business Machines Corporation (IBM) and Microsoft Corporation. An operating system is the set of software programs that controls the basic functions of a computer. The operating system coordinates and stores data entering and leaving the computer, controls the computer’s hardware (such as computer memory, keyboard, and mouse), and handles system errors.

At the time OS/2 was introduced in late 1987, the most common personal computers were IBM-compatible computers running the Microsoft Disk Operating System (MS-DOS) and computers manufactured by Apple Computer Corporation running Apple’s system for the Macintosh (Mac OS). The Macintosh operating system included multitasking, a feature that enabled computers to run several applications simultaneously. In a computer network, multitasking allows several users on different computers to have simultaneous access to the same application or data set. OS/2 was the first operating system designed for IBM-compatible personal computers that allowed multitasking.

The first version of OS/2, version 1.0, was text-oriented and lacked a graphical user interface (GUI) that would allow users to enter commands with a point-and-click input device, such as a computer mouse. A year later IBM and Microsoft released OS/2 version 1.1, which included a GUI called the Presentation Manager. The Presentation Manager interface contained icons, pictures or words on the screen that users could click on with a mouse to enter instructions. OS/2 version 1.1 also allowed users to have multiple windows open (windows are portions of the screen that each contain a different document or program) and included pull-down lists of commands that the user could choose by clicking on them with their mouse.

IBM and Microsoft ended their collaboration on OS/2 in 1991 after Microsoft released its Windows software, a multitasking environment that ran on MS-DOS. In 1992 IBM released version 2.0 of OS/2, which ran Microsoft Windows programs and could perform multitasking of DOS operations. It also contained an object-oriented programming environment that allowed software designers to create programs using high-level, object-oriented programming languages.

Subsequent versions of OS/2 offered enhanced performance and multimedia capabilities, and in 1994 IBM announced that more than 5 million copies of OS/2 had been sold since its introduction. The same year, IBM introduced a new version of OS/2 called OS/2 Warp that featured improved performance, more multimedia capabilities, an array of integrated applications, and easy access to the Internet. IBM has continued to upgrade and extend OS/2 Warp.