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Multitasking MS-DOS 4

Multitasking MS-DOS 4 refers to an intermediate operating system between MS-DOS and OS/2, which was only offered by certain original equipment manufacturers located in Europe. Unlike its predecessors and even contemporary versions of Microsoft Windows, it implements proper preemptive multitasking with a time-sliced scheduler.

The project was intended to be the successor to MS-DOS 2 and later MS-DOS 3, although it does not share much amount of code with it. The system natively supports the New Executable format from Windows 1.0 in addition to older COM and MZ executables. However, only NE format executables can be multitasked, while running legacy MS-DOS applications will suspend all background tasks. A large part of the operating system was also rewritten in C, including the entirety of the command interpreter (COMMAND.COM), several utilities (such as FDISK.EXE, the disk partition tool) and parts of the DOS kernel (IBMDOS.COM).

Documents suggest that many features such as threading were also planned but removed or otherwise scrapped during development; a successor, version 5.0, was also planned, which would have included support for threaded applications as well as support for protected mode and installable file systems. The DOS 5.0 project eventually morphed into OS/2 1.0, with early test builds shipping under the "DOS 5.0" moniker before the introduction of the OS/2 brand.