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OpenDOS

From Alfawiki
Digital Research, Inc.
Company typePrivate
IndustrySoftware
Founded1974; 52 years ago (1974)
FounderGary A. Kildall
FateAcquired by Novell, later Caldera
SuccessorNovell DOS, Caldera DR-DOS
Headquarters
Pacific Grove, California
,
United States
Area served
Worldwide
Key people
Gary A. Kildall (founder)
ProductsDR-DOS, CP/M, Concurrent DOS, DOS Plus, PalmDOS

DR-DOS (displayed as DR DOS without a hyphen through version 6.0) is a disk operating system designed for IBM PC-compatible computers. It was originally created by Digital Research, Inc., led by Gary A. Kildall, and evolved from Concurrent PC DOS 6.0, itself an advanced iteration of CP/M-86. Debuting in 1988, DR-DOS was the first DOS variant specifically developed to be compatible with both IBM PC DOS and MS-DOS.

The initial launch was version 3.31, numbered to match the contemporaneous MS-DOS release. The first retail edition, DR DOS 5.0, arrived in 1990 and garnered positive reviews, quickly establishing itself as the main rival to Microsoft's MS-DOS, which responded with its own MS-DOS 5.0 more than a year later. DR-DOS also introduced the graphical interface layer known as ViewMAX. The release of DR DOS 6.0 followed in 1991; after Novell acquired Digital Research, the product was rebranded as Novell DOS 7.0 in 1994. Later ownership by Caldera resulted in updated versions, some distributed under an open-source license as OpenDOS. The last desktop edition, Caldera DR-DOS 7.03, was issued in 1999 before the software's focus shifted toward embedded systems under Caldera and subsequently DeviceLogics.

CP/M Foundations

Digital Research initially developed CP/M for 8-bit processors such as the Intel 8080 and Z80, which led to various derivatives including CP/M-86 for the Intel 8086/8088 processors. CP/M had dominated the personal computer market since the mid-1970s and was widely bundled with non-proprietary hardware platforms. However, the introduction of the IBM PC in 1981 caused a major shift in market dynamics.

In 1980, IBM approached Digital Research to create an x86-compatible version of CP/M but withdrew following contractual disagreements. IBM then collaborated with Microsoft, which had acquired 86-DOS from Seattle Computer Products (SCP). This product evolved into Microsoft’s MS-DOS and IBM’s PC DOS. The command interface and API of 86-DOS closely mirrored those of CP/M 2.2. After Digital Research threatened legal action, IBM agreed in early 1982 to offer Digital Research’s CP/M-86 alongside PC DOS. However, CP/M-86’s price of $240 was six times higher than PC DOS’s $40, limiting its market penetration despite initially stronger software support.

Digital Research found it challenging to compete against the dominant Microsoft-IBM ecosystem and adapted their multi-tasking successors—MP/M-86, Concurrent CP/M-86—to run MS-DOS applications. This effort culminated in the public demonstration of Concurrent DOS 3.1 (CDOS with BDOS 3.1) in December 1983 and its release to hardware manufacturers in March 1984. While Concurrent DOS later evolved into Multiuser DOS and REAL/32, these solutions were expensive and ill-suited for single-user desktop environments.

To better address this market segment, Digital Research pursued two strategies: In 1985, they released DOS Plus versions 1.0 through 2.1—a simplified single-user offshoot of Concurrent DOS that supported both CP/M and DOS applications with limited multitasking capabilities. Due to incomplete DOS compatibility, Digital Research introduced a fully native DOS system in 1988 named DR DOS.

Although headquartered in Pacific Grove and later Monterey, California, much of the development work on DOS Plus took place at Digital Research Europe’s office in Newbury, Berkshire, UK beginning in 1983. From 1986 onward, major operating system development—including projects such as Concurrent DOS 386/XM, Multiuser DOS, DR DOS, and PalmDOS—was conducted at the European Development Centre (EDC) located in Hungerford, Berkshire, with additional input from Digital Research GmbH based in Munich, Germany.

Initial DR DOS Release

Responding to demands from OEM partners, Digital Research initiated development of a new DOS version in 1987 aimed at overcoming the limitations found in MS-DOS. A significant partnership with Kazuhiko "Kay" Nishi from ASCII Corporation facilitated entry into the Japanese OEM market. The inaugural DR DOS edition was introduced on May 28, 1988, with its versioning aligned to correspond with MS-DOS features. The public debut was DR DOS 3.31, which matched the capabilities of Compaq MS-DOS 3.31, including support for large disks (FAT16B/"BIGDOS"). Externally, it identified itself as "IBM PC DOS 3.31," while internally the BDOS kernel was at version 6.0—designed for single-user operation and derived from Concurrent DOS 6.0 but lacking multitasking and CP/M API compatibility, incorporating an IBM-compatible DOS-BIOS in place of the XIOS. Core system files included DRBIOS.SYS (DOS-BIOS) and DRBDOS.SYS (BDOS kernel), and the OEM disk label used was "DIGITAL␠".

DR DOS offered enhanced command-line utilities featuring help functions, detailed error messages, advanced command history and editing capabilities enabled by the HISTORY directive, as well as integrated file and directory password protection within the kernel. It was more affordable to license compared to MS-DOS and included a ROMable variant known as ROS (ROM Operating System). Interest from PC manufacturers led to several subsequent updates.

During a period when MS-DOS was predominantly tied to OEM hardware distribution, DR DOS gained market presence by being accessible through retail outlets starting with version 3.4x.

Documented versions include DR DOS 3.31 (BDOS 6.0, June 1988, OEM exclusive), 3.32 (August 17, 1988), 3.33 (September 1, 1988), 3.34, and 3.35 (October 21, 1988), all restricted to OEMs; alongside retail releases such as 3.40 (January 25, 1989) and 3.41 (BDOS 6.3, June 1989). Numerous hardware-specific variations existed; while most OEMs retained the DR DOS branding, 2001 Sales, Inc. marketed it under the name EZ-DOS 3.41 and later EZ-DOS 4.1.

DR DOS Version 5.0

Released in May 1990 under the code name "Leopard," DR DOS 5.0 maintained backward compatibility by identifying itself as "PC DOS 3.31" externally while internally operating on a single-user BDOS kernel version 6.4. The version number jumped from 3.x to avoid association with the poorly received MS-DOS 4.0 release that was skipped entirely. This update introduced ViewMAX, a graphical file manager shell based on GEM technology, accompanied by the tagline "Digital Research - We make computers work". Additionally, DR DOS 5.0 debuted the patented BatteryMAX power management system, included bundled disk-caching software named DRCACHE, a remote file transfer utility called FILELINK, a cursor customization tool labeled CURSOR, and significantly enhanced memory management through MemoryMAX. The system files were renamed to IBMBIO.COM and IBMDOS.COM, while the OEM boot sector label changed to "IBM␠␠3.3".

DR DOS 5.0 pioneered load-high functionality by relocating its kernel and critical data structures into the High Memory Area (HMA), thereby freeing up valuable conventional memory—the first 640 KB RAM segment utilized by DOS applications. On Intel 80386 processors, its EMS memory manager allowed device drivers to be loaded into upper memory blocks, further increasing available base memory.

By integrating load-high features directly into the operating system core, DR DOS 5.0 offered substantially more free conventional memory compared to other DOS variants of the time. Typical MS-DOS or PC DOS configurations running mouse drivers, multimedia software, and network components often left only about 300–400 KB free, whereas DR DOS could provide up to approximately 620 KB free—resulting in improved performance for software from the late 1980s era. Utilizing MEMMAX +V also allowed conventional memory expansion into unused graphics card RAM areas, adding an extra range of roughly 64–96 KB.

Some older applications experienced issues due to unexpected loading within low memory segments under this scheme. To address compatibility concerns, DR DOS 5.0 introduced the MEMMAX -L option which reserved memory at the beginning of the map to prevent conflicts—albeit at the expense of reduced usable conventional memory space overall. By default, MEMMAX was configured with +L enabled to maximize available memory for user applications.

DR DOS 6.0 and Microsoft Rivalry

Confronted with intense competition, Microsoft unveiled MS-DOS 5.0 in May 1990, officially launching it in June 1991. This version incorporated sophisticated capabilities akin to those found in DR DOS, such as improved memory management.

In September 1991, Digital Research introduced DR DOS 6.0, codenamed "Buxton," which internally operated on BDOS version 6.7 but identified itself as "IBM PC DOS 3.31" to maintain compatibility. This release included utilities like SuperStor for disk compression and a file deletion tracking system with undelete features developed by Roger A. Gross.

A notable feature of DR DOS 6.0 was TASKMAX, a task-switching utility compatible with the industry-standard API that enabled running multiple applications simultaneously by suspending background tasks until brought to the foreground. It leveraged XMS memory on Intel 286 and higher processors and offered limited Copy & Paste functionality. Users could replace TASKMAX's text-based menu with graphical shells such as ViewMAX or PC/GEOS through the task-switcher API.

Microsoft countered by releasing MS-DOS 6.0, incorporating many features similar to those in DR DOS.

In December 1991, the beta version of Windows 3.1 included the AARD code, which detected non-Microsoft DOS versions and displayed a non-critical error message. Digital Research promptly issued a patch for DR DOS 6.0 that circumvented this detection by rearranging internal memory structures without affecting functionality. This "business update" patch became available within six weeks of Windows 3.1's launch, enabling full compatibility with DR DOS and Novell DOS platforms.

By July 1992, Digital Research Japan had released DR DOS 6.0/V, a version compatible with the Japanese DOS/V standard, alongside a Korean edition.

PalmDOS

In 1992, under Novell's ownership since July 1991, Digital Research developed "Merlin," later marketed as NetWare PalmDOS 1—a lightweight derivative of DR DOS 6.0 designed for the emerging palmtop and PDA markets.

PalmDOS was the first in the DR DOS line to utilize the BDOS 7.0 kernel featuring native DOS-compatible internal structures, which enhanced application compatibility and reduced kernel size—an essential factor for PDA devices. However, its fully DOS-compatible Current Directory Structure (CDS) limited directory path lengths to 66 characters, unlike earlier DR DOS versions. To maintain a compact kernel and ensure Windows compatibility, PalmDOS identified itself as "PC DOS 3.31" to software applications.

Engineered for execution from ROM, PalmDOS supported PCMCIA cards with DPMS power management, technologies such as BatteryMAX and the patented dynamic idle detection driver $IDLE$, along with MINIMAX task switching for PIM applications running from ROM via execute-in-place (XIP). The PCMCIA stack development involved Ian H. S. Cullimore, a prominent contributor to the PCMCIA/PC Card standards.

Novell DOS 7 and Novell's Role

Novell DOS became Novell Corporation’s rebranding of DR DOS after acquiring Digital Research in 1991. It often outpaced MS-DOS by at least one release cycle in terms of features and performance. By 1993, Novell’s DOS 7 had surpassed IBM’s PC DOS 6.1 and Microsoft’s MS-DOS versions 6.2 and 6.3.

Novell CEO Robert J. Frankenberg pursued significant product line reductions by divesting offerings such as Btrieve and discontinuing others including Novell DOS itself and WordPerfect multimedia products. Novell licensed technology from Stac Electronics for use in both Novell DOS and its NetWare network operating system. On July 23, 1996, Novell sold the DR DOS product line to Caldera, which intended to bundle it with OpenLinux.

Marc Perkel claimed credit for influencing Novell’s acquisition of Digital Research and proposing the "NovOS" concept in early 1991. Novell sought to challenge Microsoft's market dominance through DR's technology; however, delays affected DR DOS 7.0 ("Panther"), leading to abandonment of planned Unix-like multi-user security extensions and graphical interfaces such as ViewMAX 3 and the Apple System 7 port dubbed "Star Trek."

Launched in December 1993 as Novell DOS 7 (NWDOS), this release omitted these ambitious features but was widely regarded by experts as the most advanced DOS available despite some increased size and incomplete elements.

In Germany, Novell aggressively promoted DOS 7 with the slogan "" ("Don't trust any DOS below 7"), achieving approximately 1.5 million units sold by February 1994 and securing over 3000 dealers. Distribution channels included OEM partnerships, mail order sales, and authorized resellers.

A significant enhancement was Personal NetWare (PNW), Novell's upgraded peer-to-peer networking solution incompatible with Microsoft's networking protocols; it required complex setup alongside Windows networks and experienced limited commercial success.

Novell DOS 7 incorporated an updated BDOS kernel version 7.2 that reported itself as DOS version 6.0 with OEM ID "IBM" to maintain Windows compatibility while exposing advanced memory management features such as DPMI and DPMS support alongside flexible loadhigh options.

It introduced genuine pre-emptive multitasking of multiple DOS applications via virtual DOS machines (VDMs) through MultiMAX technology. In combination with EMM386 /MULTI, it provided a native 32-bit protected mode kernel supporting multitasking, multi-threading, virtualization, and domain management accessible through an API for DR DOS-aware software. The included TASKMGR utility utilized this API to deliver efficient task management compatible with Windows environments.

Both Novell DOS 7 and Personal NetWare came bundled with NetWars, a network-enabled three-dimensional arcade game.

Despite several bug-fix updates (D70xyy), Novell DOS 7 was not entirely stable when Microsoft released Windows 95 beta versions. Development ceased in September 1994, with maintenance concluding in January 1996 after more than fifteen updates had been issued.

Post-Novell Era

In search of a DOS operating system to package with their OpenLinux distribution, Caldera acquired the product line from Novell on July 23, 1996, as Novell considered it commercially insignificant.

Microsoft limited Windows 95 compatibility strictly to their own DOS platform in response to competition from IBM's PC DOS 6.3 and Caldera's DR-DOS. This restriction triggered a significant lawsuit, financially backed by the Canopy Group. Although Microsoft attempted to dismiss the lawsuit, it was ultimately resolved out of court on January 7, 2000, for $280 million, a settlement disclosed in 2009.

In August 1996, Roger A. Gross, one of the original engineers behind DR-DOS, suggested reviving DR-DOS development and enabling Windows 95 compatibility to strengthen the legal case. After discussions with Caldera’s leadership, Gross was employed to establish a UK branch. On September 10, 1996, Caldera announced plans for OpenDOS (COD) and the intention to release its source code publicly. Shortly thereafter, Caldera UK Ltd. was founded.

Gross assembled a team including former Novell EDC developers and fresh talent at a site near Andover in Hampshire, UK. Over two years, significant enhancements were incorporated: a TCP/IP stack derived from LAN WorkPlace for DOS/NetWare Mobile, a 32-bit protected mode HTML 3.2 browser (DR-WebSpyder) based on Arachne (web browser), POSIX Pthreads extensions, support for long filenames (LONGNAME), and FAT32 capability (DRFAT32). Andrew Schulman joined as a consultant for "WinGlue," an initiative to develop Windows 95/98 compatible DR-DOS variants replacing Microsoft DOS components. Demonstrated at CeBIT in March 1998, this project evolved into "WinBolt," which remained unreleased but played a critical role in the legal proceedings.

On February 3, 1997, Caldera UK launched Caldera OpenDOS 7.01—a rebranded update of Novell DOS 7 update 10 that lacked patches from later Novell releases due to lost source code at Novell. It excluded utilities such as SETFIFO and omitted virus scanners previously bundled with Novell DOS but included updated tools like PNUNPACK and an enhanced version of NetWars.

Some portions of OpenDOS 7.01 were briefly made available as open source in May 1997 but were subsequently closed again owing to licensing issues and commercial considerations.

After beta versions late in 1997, Caldera released DR-OpenDOS 7.02 in December of that year (later renamed Caldera DR-DOS 7.02). This edition featured improved BIOS and BDOS modules with numerous compatibility corrections and optimizations by Matthias R. Paul. It enhanced interoperability with Windows 9x and third-party disk compression drivers such as DriveSpace.

Version 7.02 introduced diagnostic boot modes, integrated debugger functionality, advanced CONFIG.SYS tracing along with scripting capabilities that allowed flexible boot menus and interactive user prompts, plus improved multi-configuration support through LOADER and CHAIN commands. Memory management was refined with load-high features freeing conventional memory for third-party drivers and shells like 4DOS.

National Language Support received upgrades via hierarchical COUNTRY.SYS files enabling simultaneous multi-locale support, recognition of ISO 8601 date formats including Euro currency handling, and Year 2000 compliance incorporating BIOS bug fixes. The updated FDISK utility supported FAT32 partitioning initially without LBA functionality. Subsequent patches restored missing Novell DOS updates discovered in Germany.

The BDOS version upgrade caused some legacy software failures; however, enhancements to the SETVER utility allowed DR-DOS to emulate earlier DOS versions or suppress BDOS version checks to maintain compatibility.

New HIFILES features introduced conflicts with QEMM 8’s DOS-UP memory manager requiring a patch (IBMBIO85.SCR) that balanced compatibility across Windows versions and memory management schemes.

In August 1998, Caldera formed two subsidiaries: Caldera Systems, Inc., concentrating on Linux solutions, and Caldera Thin Clients, Inc., targeting embedded systems and thin-client markets.

Caldera UK officially released DR-DOS 7.03 on January 6, 1999, incorporating improved memory managers with enhanced DPMI multitasking support plus additional utilities like DEVLOAD and DRMOUSE. A modified FAT OEM label caused some cross-operating system issues but could be bypassed using NOVOLTRK. This marked the final desktop-focused DR-DOS release.

Following Roger Gross’s departure early in 1999, Caldera shifted DR-DOS development back to the United States; the successful UK operation was closed down. Development efforts suffered due to lack of expertise stateside. The DR-DOS product line was transferred to Caldera Thin Clients—renamed Lineo, Inc.—on July 20, 1999. Lineo reissued DR-DOS 7.03 under the "Caldera DR-DOS" brand but redirected focus toward embedded Linux platforms built on a streamlined OpenLinux variant called Embedix.

Independent OEM editions followed: DR-DOS 7.04 (August 19, 1999) and 7.05 (November 30, 1999), still marketed as "Caldera DR-DOS." These minimal kernel-and-shell versions supported native FAT32 and large disk capacities and were bundled with utilities such as Ontrack's Easy Recovery 5 (replacing prior dynamic DRFAT32 drivers), Seagate's SeaTools, and Nero Burning ROM. Internally they identified as "PC DOS 7.10" reflecting FAT32 integration while preserving backward compatibility.

Further evolution of DR-DOS included:

  • Version 7.06 (December 14, 1999), which consolidated kernel components into a single executable bootable via MS-DOS 7.10 boot sectors but incompatible with traditional DR-DOS sectors.
  • Version 7.07 introduced unified bootstrap loaders supporting CHS/LBA disk access across FAT12/16/32 file systems and multiple OS boot protocols including PC DOS/MS-DOS/Windows/REAL/32/LOADER through a single NEWLDR master boot record and boot sector module. This facilitated multi-boot configurations by enabling any DR-DOS version from as early as 3.31 to load alongside other operating systems.

These technological improvements extended DR-DOS’s applicability within embedded environments despite diminishing desktop relevance as Lineo shifted strategy toward Linux-based embedded solutions.

Later iterations

Following the acquisition of Lineo in 2002, former Lineo executives established DRDOS, Inc., operating as DeviceLogics L.L.C., and continued marketing DR-DOS tailored for embedded applications. On March 30, 2004, DR-DOS 8.0 was released, introducing support for FAT32 and large storage devices, the ability to boot from ROM or Flash memory, multitasking capabilities, and a DPMI memory manager—all built upon kernel version 7.03.

The autumn of 2005 saw the arrival of DR-DOS 8.1, which enhanced FAT32 functionality and was based on OpenDOS 7.01.xx. Nevertheless, this version was subsequently retracted due to violations of the GPL (refer to Controversies). Additionally, DRDOS, Inc. proposed an option to purchase the DR-DOS rights for $25,000.

The source code from OpenDOS 7.01 served as the foundation for The DR-DOS/OpenDOS Enhancement Project initiated in July 2002 aimed at updating DR-DOS. This initiative brought native large disk (LBA) support, FAT32 compatibility improvements, advanced memory handling, and FAT32+ which allowed files up to 256 GB on FAT partitions. A work-in-progress release, DR-DOS 7.01.08 WIP, became available on July 21, 2011.

Starting in 2023, the latest Enhanced DR-DOS version (7.01.08 WIP) was adapted to an open-source build system that facilitates cross-compilation from non-DOS platforms. The kernel compiles into a single binary file named KERNEL.SYS, compatible with FreeDOS boot loaders. This release has undergone various bug fixes and updates and continues to be actively maintained as of October 2024.

Controversies

In October 2005, it was discovered that DR-DOS 8.1 incorporated utilities sourced from FreeDOS and other projects without adhering to the GNU General Public License (GPL) terms—specifically neglecting to credit original authors or provide access to source code. Following concerns raised by FreeDOS contributors demanding compliance, DRDOS, Inc. removed versions 8.1 and 8.0 from its distribution site.

Commands

From DR-DOS version 3.31 onward, internal commands included APPEND, ASSIGN, BATCH, DBG, DELQ, ERA, ERAQ, MORE, and SUBST. The release of DR-DOS 5.0 saw the removal of BATCH and the introduction of HILOAD.[1][2] With DR-DOS 6.0 came new internal commands such as GOSUB, IDLE, RETURN, and SWITCH; meanwhile ASSIGN and SUBST were converted into external commands.[2] Commands ECHOERR and PAUSEERR existed internally in version 6.0 but were generally disabled by default.[1] The MORE command remained internal through PalmDOS but transitioned to external with Novell DOS 7; DBG was eliminated by Novell DOS 7 or possibly earlier releases. Internal additions including LOADHIGH (LH) and TRUENAME appeared starting with update 8 and DR DOS 6.0 (1993). While APPEND was internal in DR-DOS 6.0, it became external under Novell DOS 7.

Internal commands

Below is a compilation of internal commands supported by DR DOS 6.0:


Batch processing subcommands

The batch processing subcommands available in DR DOS 6.0 encompass the following:

External commands

The following external commands are supported by DR  DOS 6.0:

See also

Further reading

  • Digital Research, Inc. (1990). DR DOS 5.0 Retail box with lid. Digital Research, Inc. Part Number 1176-6114-001.
  • Digital Research, Inc. (May 1990). DR DOS 5.0 User Guide, 1st ed., 501 pages. Digital Research, Inc. Part Number 1176-2004-002.
  • Digital Research, Inc. (May 1990). ViewMAX User Guide, 1st ed., 88 pages. Digital Research, Inc. Part Number 1174-2004-002.
  • Digital Research, Inc. (August 1990). DR DOS 5.0 Release Notes, 11 pages. Digital Research, Inc. Part Number 1176-1001-002.
  • Digital Research, Inc. (August 1991). DR DOS 6.0 Software performance report. Digital Research, Inc. Part No. 000-1200-00.
  • Digital Research, Inc. (August 1991). DR DOS 6.0 User Guide, 2nd ed., 698 pages. Digital Research, Inc. Part Number 1182-2004-002.
  • Digital Research, Inc. (August 1991). ViewMAX User Guide, 2nd ed., 106 pages. Digital Research, Inc. Part Number 1192-2054-002.
  • Novell Desktop Systems Group (January 7, 1993). DRTIPS.ZIP. Published by Digital Research / Novell.

External links

  1. ↑ 1.0 1.1 Cite error: Invalid <ref> tag; no text was provided for refs named Paul_1997_DRDOS6UN
  2. ↑ 2.0 2.1 Cite error: Invalid <ref> tag; no text was provided for refs named 4DOS_8.00_HELP
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