History

IBM and Microsoft** introduced OS/2 in 1987 as a successor to the PC DOS/MS DOS** operating system [For simplicity, the term "DOS" will be used throughout this document to refer to both the PC DOS and MS DOS products. ] in the programmable workstation environment. In the years since its inception in the early 1980s, DOS has grown in both capabilities and sophistication, but by 1987 advanced workstation users were demanding more sophistication from their applications, to an extent which was beyond the capabilities of DOS to deliver.

The choice for operating system developers lay between further enhancing the existing DOS architecture to support more powerful processors, larger memory and so on, or migrating to a new, more powerful operating system architecture which offered more facilities to satisfy user requirements, a broader platform for application development, and potential for future expansion. The latter choice was taken, and the result was OS/2.

The OS/2 operating system environment provides a great deal more power and flexibility than the DOS environment, while maintaining a level of compatibility with existing DOS applications and data. Enhancements made in OS/2 Version 1.3 include:

  • Effective use of the advanced capabilities of the Intel 80286 processor

  • Support for system memory above 640 kilobytes (KB)

  • Support for multiprogramming and multitasking

  • Dynamic linking for system and application modules.

    In addition, numerous other functions are provided to support and complement these capabilities.

    OS/2 Version 2.0 was developed as an extension of the original 16-bit implementation used in OS/2 Version 1.3, and is an advanced 32-bit multitasking operating system for machines equipped with the Intel 80386** or compatible processors. The following new features are implemented in OS/2 Version 2.0:

  • Support for the Intel 80386 32-bit microprocessor instruction set; previous versions of OS/2 only supported the 80386 in 80286 emulation mode.

  • 32-bit memory management with a flat memory model; previous versions of OS/2 required applications to use the segmented memory model. See Memory Management for further information.

  • Enhanced hardware exploitation.

  • Support for multiple concurrent DOS applications with pre-emptive multitasking and full memory protection.

  • Support for Microsoft Windows** applications.

  • New 32-bit programming environment.

  • Binary-level compatibility with previous versions of OS/2, allowing 16-bit applications written for previous versions to execute under Version 2.0 without modification.

  • An enhanced Presentation Manager user shell, known as the Workplace Shell, which implements the 1991 IBM Systems Application Architecture CUA Workplace Environment.

    The remainder of this chapter describes the features of OS/2 Version 2.0, and also makes reference to architectural features implemented in previous versions of OS/2 where appropriate.

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