![]() For example, a powerful telephone management system could be built into a PC by using special MS-DOS version 4.0 background processes to control the telephone equipment. Only one MS-DOS version 3.x compatible real mode application can be run the other processes must be special MS-DOS version 4.0 processes that understand their environment and cooperate with the operating system to coexist peacefully with the single MS-DOS version 3.x real mode application.īecause of these restrictions, MS-DOS version 4.0 was not intended for general release, but as a platform for specific OEMs to support extended PC architectures. Although MS-DOS version 4.0 supports full preemptive multitasking, system memory is limited to the 640 KB available in real mode, with no swapping.2 This means that all processes have to fit into the single 640 KB memory area. The limitations of the real mode environment make MS-DOS version 4.0 a specialized product. Because MS-DOS version 4.0 runs only in real mode, it can run on 80 machines as well as on 80286 machines. A version of this product–a multitasking, real-mode only MS-DOS–was shipped as MS-DOS version 4.0. When a new version of the single-tasking MS-DOS was shipped under the name MS-DOS version 3.0, the multitasking version was renamed, internally, to MS-DOS version 4.0. At the time, it was internally called MS-DOS version 3.0. ![]() Microsoft started work on a multitasking version of MS-DOS in January 1983. With the pre-christmas release of the Microsoft OS/2 betas 1.00, 1.01, 1.02, 1.03 & 1.05 on, and helping Ncommander with an upcoming video, it seemed like a good place to start, not with OS/2 but rather with MS-DOS 4.0.įrom the book INSIDE OS/2 ( ISBN 1-55615-117-9 )
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