From Academic Kids

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



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 make 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 the early 1980s were all but unanimous in the view that CP/M-86 was technically superior, and that the marketplace would eventually favour it. However, the experts had not reckoned on the marketing savvy of Microsoft or the then-mighty power of IBM's name: the proportion of PC buyers prepared to spend the extra to buy CP/M-86 gradually declined, and the availability of compatible application software, originally decisively in Digital Research's favour, soon became a negative factor.

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, wanting to avoid comparison with the abysmal 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. As well as bundling a 386-mode memory manager, capable of converting Extended Memory Specification (XMS) memory into Expanded Memory Specification (LIM 4.0 EMS) memory - which was more commonly used by DOS applications - it 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.

Additionally, on Intel 80386 machines, DR-DOS 5 included an EMS memory manager with the basic functionality of third-party equivalents such as Quarterdeck's QEMM. This enabled the OS to load DOS device drivers into upper memory blocks. For more information on this, see the article on the Upper Memory Area.

DR-DOS 5 was the first DOS to integrate such functionality into the base OS. As such, on a 386 system, it could offer vastly more free conventional memory than any other DOS. Once drivers for a mouse, multimedia hardware and a network stack were loaded, an MS-DOS machine typically might only have 300 to 400KB of free conventional memory - too little to run most late-1980s software. DR-DOS 5, with a small amount of manual tweaking, could load all this and still keep all of its conventional memory free - allowing for some necessary DOS data structures, as much as 620KB out of the 640KB.

So much, in fact, that some programs would fail to load as they started "impossibly" low in memory - inside the first 64KB. DR-DOS 5's new LOADFIX command worked around this by leaving a small empty space at the start of the memory map.

Given the constraints of the time, this was an incredibly powerful technology which made life much easier for PC technicians of the day, and this propelled DR-DOS 5.0 to rapid and considerable popularity.

Aggressive competition by Microsoft

Suddenly faced with real competition in the DOS arena for the first time, Microsoft started an aggressive campaign to downplay the product. They immediately announced the development of MS-DOS 5.0 in May 1990, to be released a few months later and include all the advanced features of DR-DOS. This turned out to be a famous case of vaporware, as MS-DOS 5.0 was actually not released until June 1991. Although it included copies of almost all of DR's enhancements in memory management, it did not offer all of the improvements to the syntax of DOS commands that DR did.

DR responded with DR-DOS 6.0 in 1991. This bundled in SuperStor on-the-fly disk compression, to maximise the space available on the tiny hard disks of the time - 40MB was still not an atypical size, which with the growth of larger applications and especially Microsoft Windows was frequently not enough space. DR-DOS 6.0 also included an API for multitasking on CPUs capable of memory protection, namely the Intel 80386 and newer. The API was available only to DR-DOS aware applications, but well-behaved ordinary DOS applications could also be pre-emptively multitasked by the bundled task-switcher, TaskMax. On 286-based systems, DOS applications could be suspended to the background to allow others to run. However, DR's multitasking system was technically inferior to third-party offerings such as DESQview, which could multitask applications which performed direct hardware access and graphical applications and even present them in scalable on-screen windows, and it was never widely used. It nonetheless represented an important "tick on the box" - a feature on the list of specifications which Microsoft could not rival.

Microsoft responded with MS-DOS 6.0, which again copied the more important features of DR-DOS 6.0 - but the use of stolen code caused legal problems. See the article on MS-DOS for more.

Though DR-DOS was almost 100% binary compatible with applications written for MS-DOS, Microsoft nevertheless expended considerable effort in attempts to break compatibility. In one example, they inserted code into Windows 3.0 to return a non-fatal error message if it detected a non-Microsoft DOS. With the detection code disabled (or if the user canceled the error message), Windows ran perfectly under DR-DOS. (see also Embrace, extend and extinguish for other Microsoft tactics.)

Patching to counter Microsoft

In the fall/Autumn of 1991 Microsoft announced Windows 3.1, complete with modifications to ensure that it would not run on the then-new DR-DOS 6.0. (They had also refused to allow DR access to the beta of 3.1.) It was a simple matter for Digital Research to patch DR-DOS to circumvent the modifications, and the patched version was on the streets within six weeks of the release of Windows 3.1. With improved marketing and packaging, very advanced memory management, disk compression and the Super PC-Kwik caching software, DR-DOS 6.0 was outstanding value and easily the most successful version.

Around this time, networking giant Novell bought Digital Research with a view to using DR's product line as a lever in their comprehensive strategy to break the Microsoft monopoly. (This was part of a massive and ultimately disastrous spending spree for Novell: they bought WordPerfect Corporation at about the same time, some of Borland's products, and invested heavily in Unix as well.) The planned DR-DOS 7.0, intended to trump Microsoft's troubled MS-DOS 6.0, was repeatedly delayed. When it eventually arrived -- renamed to Novell DOS 7.0 -- it was a disappointment. It was bigger and introduced many new bugs and the main functional addition was Novell's second attempt at a peer-to-peer networking system, Personal Netware. This worked and was better than its predecessor Netware Lite but it was incompatible with Microsoft's networking system, now growing popular with both Windows for Workgroups and both OS/2 and Windows NT-based networking systems. A considerable amount of manual configuration was needed to get both to co-exist on the same PC and Personal Netware never achieved much success.

Contribution by Novell

Novell DOS 7 required several bug-fix releases and was not completely stable when the next development occurred. Realising eventually that their formidable networking skills did not translate into other areas, Novell sold the product line off to Caldera Systems, by which time it was of little commercial value.

Although DR-DOS had ceased to be a significant present threat to their market share by 1995, Microsoft now faced growing competition from IBM's PC-DOS 6.3, and moved to make it impossible to use or buy the subsequent Windows version, Windows 95, with any other DOS product bar their own. Claimed by them to be a purely technical change, this was later to be the subject of a major law suit brought in Salt Lake City by Caldera. Microsoft lawyers tried repeatedly to have the case thrown out but without success. Immediately after the completion of the pre-trial deposition stage (where the parties list the evidence they intend to present), there was an out-of-court settlement for an undisclosed but massive sum. DR-DOS was eventually sold to Lineo, where it is still manufactured for some specialised applications. One of those applications is Seagate's Seatools, which boots into a version of DR-DOS.

Current Versions

DR-DOS 7.01, which was released by Caldera under a non-commercial use only source code license as OpenDOS, is still actively being developed by The DR-DOS/OpenDOS Enhancement Project (http://www.drdosprojects.de/), founded in July 2002 in an attempt to bring the functionality of DR-DOS up to parity with modern PC operating systems. The project's efforts have resulted so far in adding native support for large disks (LBA) and the FAT32 filesystem.

In 2002, DR-DOS was sold to a small Lineo spin-off company called DeviceLogics, which has continued to sell it for use in embedded systems. DR-DOS 8.0 was released on 30 March 2004 featuring FAT32 and large disk support, the ability to boot from ROM or Flash, multitasking and a DPMI memory manager.

See also

External links

Current Versions



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