Editing DR-DOS (section)

==={{anchor|6.0|6.0 business update|6.0/V}}DR&nbsp;DOS 6.0 / Competition from Microsoft===
[[File:DR-DOS 6.0 Digital Research.jpg|thumb|Digital Research DR&nbsp;DOS 6.0 startup disk]]
[[File:ManualDRDOS60.jpg|thumb|Novell DR&nbsp;DOS 6.0 manual]]
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.<ref name="Caldera_1996_Suit"/> This would be released in June 1991<ref name="Caldera_1996_Suit"/> and include similar advanced features to those of DR&nbsp;DOS.<ref name="Dryfoos_1991_DOS5"/> It included matches of the DR's enhancements in memory management.<ref name="Dryfoos_1991_DOS5"/>

Almost immediately in September 1991, Digital Research responded with DR&nbsp;DOS 6.0,<ref name="Caldera_1996_Suit"/> code-named "Buxton". DR&nbsp;DOS 6.0, while already at BDOS level 6.7 internally, would still report itself as "IBM PC&nbsp;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&nbsp;DOS 6.0 also included a task-switcher named TASKMAX<ref name="Salemi_1991_DR6"/> with support for the industry-standard task-switching API<!-- INT 2Fh/4Bh --><ref name="Caldera_1997_Multi"/> 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&nbsp;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.<ref name="Salemi_1991_DR6"/> TASKMAX did support some [[Copy & Paste]] facility between applications.<ref name="Salemi_1991_DR6"/>
Via the task-switcher API, graphical user interfaces such as [[ViewMAX]]<ref name="Salemi_1991_DR6"/> 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&nbsp;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.<ref name="Caldera_1996_Suit"/> This check came to be known as the [[AARD code]].<ref name="Chappell_AARD"/><ref name="Egbert_1998"/> It was a simple matter for Digital Research to patch DR&nbsp;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.<ref name="CW_1992"/><ref name="Schulman_1994_Undocumented-DOS"/><ref name="Caldera_1999_Statement_of_facts"/><ref name="Paul_2000_History"/> With the detection code disabled, Windows ran perfectly under DR&nbsp;DOS and its successor Novell DOS. The code was present but disabled in the released version of Windows 3.1.<ref name="DDJ"/>

In July 1992, [[Digital Research Japan]] released DR&nbsp;DOS 6.0/V, a Japanese [[DOS/V]] compatible version of DR&nbsp;DOS 6.0.<ref name="Timeline_2014_DOSV"/><ref name="DRDOS60V_ViewMAX"/> A Korean version appears to have been available as well.