page_title: DR-DOS
section_title: DR DOS 6.0 / Competition from Microsoft
hierarchical_section_title: DR-DOS / History / DR DOS 6.0 / Competition from Microsoft
caption_attribution_description: Español: Manual del Usuario del DR-DOS 6.0
context_page_description: DR-DOS is an operating system of the DOS family, written for IBM PC-compatible personal computers. It was originally 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.
context_section_description: Faced with substantial competition in the DOS arena, Microsoft responded with an announcement of a yet-to-be released MS-DOS 5.0 in May 1990. This would be released in June 1991 and include similar advanced features to those of DR DOS. It included matches of the DR's enhancements in memory management.
  Almost immediately in September 1991, Digital Research responded with DR DOS 6.0, code-named "Buxton". DR DOS 6.0, while already at BDOS level 6.7 internally, would still report itself as "IBM PC DOS 3.31" to normal DOS applications for compatibility purposes.
  This bundled in SuperStor on-the-fly disk compression, to maximize available hard disk space, and file deletion tracking and undelete functionality by Roger A. Gross.
  DR DOS 6.0 also included a task-switcher named TASKMAX with support for the industry-standard task-switching API to run multiple applications at the same time. In contrast to Digital Research's Multiuser DOS (successor of Concurrent DOS in the multi-user products line), which would run DOS applications in pre-emptively multitasked virtual DOS machines, the DR DOS 6.0 task switcher would freeze background applications until brought back into the foreground. While it ran on x86-machines, it was able to swap to XMS memory on 286+ machines. TASKMAX did support some Copy & Paste facility between applications.
  Via the task-switcher API, graphical user interfaces such as ViewMAX or PC/GEOS could register as the task manager menu and thereby replace the TASKMAX text mode menu, so that users could switch between tasks from within a GUI.
  Microsoft responded with MS-DOS 6.0, which again matched some features of DR DOS 6.0.
  In December 1991, a pre-release version of Windows 3.1 was found to return a non-fatal error message if it detected a non-Microsoft DOS. This check came to be known as the AARD code. It was a simple matter for Digital Research to patch DR DOS 6.0 to circumvent the AARD code 'authenticity check' in the Windows 3.1 beta by rearranging the order of two internal tables in memory (with no changes in functionality), and the patched version, named "business update", was on the streets within six weeks of the release of Windows 3.1. With the detection code disabled, Windows ran perfectly under DR DOS and its successor Novell DOS. The code was present but disabled in the released version of Windows 3.1.
  In July 1992, Digital Research Japan released DR DOS 6.0/V, a Japanese DOS/V compatible version of DR DOS 6.0. A Korean version appears to have been available as well.
caption: Novell DR DOS 6.0 manual
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