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DR-DOS (written as DR DOS, without a hyphen, in versions up to and including 6.0) is a disk operating system for IBM PC compatibles. Upon its introduction in 1988, it was the first DOS that attempted to be compatible with IBM PC DOS and MS-DOS (which were the same product sold under different names).
DR-DOS was developed by Gary A. Kildall's Digital Research and derived from Concurrent PC DOS 6.0, which was an advanced successor of CP/M-86. As ownership changed, various later versions were produced with names including Novell DOS and Caldera OpenDOS.

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