Games - DR-DOS

	Games - DR-DOS

DR-DOS is a DOS-family-compatible operating system for IBM PC-compatible personal computers, originally developed by Gary Kildall's Digital Research and derived from CP/M-86.

History

Origins in CP/M

DR-DOS was a new name given to what was then the latest version of Digital Research's long line of computer operating systems. Their original CP/M for 8-bit 8080, Z-80, and 8085 based systems spawned numerous spin-off versions, most notably CP/M-86 for the Intel 8086/8088 family of processors. Although CP/M had dominated the market up until this time and was shipped with the vast majority of non-proprietary-architecture personal computers, the IBM PC in 1981 brought the beginning of what was eventually to be a massive change.

Rather than licence CP/M-86 from Digital Research (as the other 8088-based computer makers had done) IBM chose to equip disk based IBM PCs with PC-DOS as standard, and offer CP/M-86 as an extra-cost option. (PC-DOS, for practical purposes, could at that time be regarded as essentially identical with MS-DOS. Both products were based on Seattle Computer Products QDOS, itself a legally questionable clone of CP/M.) Experts and industry observers in late 1981 were all but unanimous in the view that CP/M-86 was technically superior, and that the marketplace would eventually favour it. However, CP/M-86 was not yet ready at the August 1981 IBM PC introduction, and Microsoft agreed with IBM to sell PC-DOS for $60 compared to the $240 being charged by Digital Research. The proportion of PC buyers prepared to spend four times as much to buy CP/M-86 was very small, and the availability of compatible application software, at first decisively in Digital Research's favour, was only temporary.

Digital Research fought a long losing battle to promote CP/M-86, and eventually decided that they could not beat the Microsoft-IBM lead in application software availability, so they had best join it by modifying CP/M-86 to allow it to run the same applications as MS-DOS and PC-DOS. The new version was re-launched in 1988 as DR-DOS.

First DR-DOS version

The first version was released in May, 1988. Version numbers were chosen to reflect features relative to MS-DOS; the first version promoted to the public was DR-DOS 3.41, which offered comparable but better features to the massively successful MS-DOS 3.3 - and Compaq's version, Compaq DOS 3.31. (Compaq's variant was the first to introduce the system for supporting hard disk partitions of over 32MB which was later to become the standard used in MS-DOS 4.0 and all subsequent releases.)

At this time, MS-DOS was only available bundled with hardware, so DR-DOS achieved some immediate success as it was possible for consumers to buy it through normal retail channels. Also, DR-DOS was cheaper to license than MS-DOS. As a result, DRI was approached by a number of PC manufacturers who were interested in a third-party DOS, and this prompted several updates to the system.

Most significant update

The most significant was DR-DOS 5.0 in May 1990. (The company skipped version 4, avoiding comparison with MS-DOS 4.0.) This introduced ViewMAX, a GEM based GUI file management shell, and bundled disk-caching software, but more significantly, it also offered vastly improved memory management over MS-DOS. Compared to earlier MS-DOS 4.01 which already bundled a 386-mode memory manager (EMM386.SYS), capable of converting Extended Memory Specification (XMS) memory into Expanded Memory Specification (LIM 4.0 EMS) memory more commonly used by DOS applications, memory management in DR-DOS had two extra features.

First, on Intel 80286 or better microprocessors with 1MB or more RAM, the DR-DOS kernel and structures such as disk buffers could be located in the High Memory Area, the first 64KB of extended memory which were accessible in real mode due to an incomplete compatibility of the 80286 with earlier processors. This freed up the equivalent amount of critical "base" or Conventional memory, the first 640KB of the PC's RAM – which was the area in which all MS-DOS applications had to run. Using high memory was not a new idea, as this memory could previously be used by Windows applications starting with Windows/286 2.1 released in 1988, but offering more memory to old DOS applications was more interesting.

Additionally, on Intel 80386 machines, DR-DOS's EMS memory manager allowed the OS to load DOS device drivers into upper memory blocks, further freeing base memory. For more information on this, see the article on the Upper Memory Area.

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