Jump to content

Concurrent DOS 386/MGE

From Alfawiki
Adapted from the English Wikipedia article Concurrent DOS 386/MGE, available under CC BY-SA 4.0Updated 9 August 2025
Multiuser DOS
Company typeOperating system
IndustryComputer software
PredecessorConcurrent CP/M-86, Concurrent DOS, Concurrent DOS 386
Founded1982
FounderDigital Research
FateDiscontinued by Novell in 1992; licensed to VARs for further development
SuccessorDatapac Multiuser DOS and System Manager, CCI Multiuser DOS, IMS Multiuser DOS, REAL/32
Area served
IBM PC-compatible microcomputers
Key people
Kathryn Strutynski (project manager), Francis "Frank" R. Holsworth (designer)
ProductsMultiuser DOS operating system and variants
OwnerOriginally Digital Research; acquired by Novell in 1991
ParentDigital Research; later Novell

Multiuser DOS is a real-time, multi-user, multitasking operating system designed for IBM PC-compatible microcomputers. It originated from earlier Digital Research products such as Concurrent CP/M-86, Concurrent DOS, and Concurrent DOS 386. Initially created by Digital Research, the system was acquired and further enhanced by Novell in 1991. Its lineage extends back to the 8-bit Digital Research operating systems CP/M and MP/M, as well as the 16-bit single-tasking CP/M-86.

Following Novell's discontinuation of Multiuser DOS in 1992, three principal value-added resellers (VARs)—DataPac Australasia, Concurrent Controls, and Intelligent Micro Software—received licenses to continue independent development. These companies released their own versions including Datapac Multiuser DOS and System Manager, CCI Multiuser DOS, and IMS Multiuser DOS along with REAL/32.

The associated FlexOS family, which evolved from Concurrent DOS 286 and Concurrent DOS 68K, was sold to Integrated Systems, Inc. (ISI) in July 1994.

Concurrent CP/M-86

The first iteration of CP/M-86 1.0 (utilizing BDOS 2.x) was adapted for the IBM PC in 1982 but failed commercially due to competition from IBM’s more affordable PC DOS 1.0. Both operating systems lacked the capability to fully exploit the new 16-bit hardware features.

Shortly thereafter, MP/M-86 2.0 introduced multitasking and multiuser functionality through dumb terminals connected via serial ports, enabling several users to operate simultaneously as if each had exclusive access to the PC. This method provided considerable cost advantages compared to purchasing multiple personal computers and supported shared-data applications like accounting or inventory management before PC networking became widespread.

By late 1982, CP/M-86 1.1 (BDOS 2.2) combined with MP/M-86 2.1 resulted in Concurrent CP/M-86 3.0 (BDOS 3.0). The development team was led by project manager Kathryn Strutynski together with designer Francis "Frank" R. Holsworth. Initially designed as a single-user OS supporting multitasking of up to four CP/M-86 compatible programs, it incorporated multi-processor capabilities and "virtual screens" for switching among tasks. Subsequent releases added multiuser support via dumb terminals. Concurrent CP/M-86 3.1 (BDOS 3.1) became available on 21 February 1984.

Concurrent CP/M-86 with Windows

In February 1984, Digital Research launched Concurrent CP/M with Windows for the IBM Personal Computer and Personal Computer XT, a variant of Concurrent CP/M-86 that introduced windowing functionality.

Concurrent CP/M-86/80

This version of Concurrent CP/M-86 was developed for the LSI-M4, LSI Octopus, and CAL PC machines, which featured both 16-bit and 8-bit processors. Concurrent CP/M-86/80 allowed execution of both CP/M (8-bit) and CP/M-86 (16-bit) software by directing programs to run on the appropriate processor according to file extensions (.COM or .CMD). It simulated the CP/M environment for 8-bit applications by converting system calls into their CP/M-86 equivalents processed on the 16-bit CPU.

Concurrent DOS

In August 1983, Bruce Skidmore, Raymond D. Pedrizetti, Dave Brown, and Gordon Edmonds created PC-MODE, an optional extension for Concurrent CP/M-86 3.1 (BDOS 3.1), enabling fundamental compatibility with PC DOS 1.1 (and MS-DOS 1.1). This module was showcased at COMDEX in December 1983 and became available to hardware manufacturers in March 1984 under the name Concurrent DOS 3.1 (CDOS with BDOS 3.1). It allowed straightforward DOS software that did not directly access hardware—such as PKZIP—to operate properly, whereas applications requiring direct screen control (for example, WordStar for DOS) needed versions native to Concurrent CP/M.

While development of Concurrent DOS versions up to 4.1 was conducted by US teams, Digital Research Europe’s OEM Support Group based in Newbury, UK managed the OEM customizations and localizations from 1983 onward.

In 1985, Digital Research marketed Concurrent DOS 4.1 combined with GEM as a competitor to IBM's TopView. Concurrent DOS 4.1 (BDOS 4.1) supported PC DOS 2.x compatibility and was offered across various hardware platforms; the IBM PC compatible variant was labeled Concurrent PC DOS 4.1.

Concurrent PC DOS

Concurrent DOS 3.2 (BDOS 3.2), released in 1984, maintained compatibility with CP/M-86 1.x, Concurrent CP/M-86 3.x, and PC DOS 2.0 applications. It operated on multiple hardware configurations; the IBM PC-compatible BIOS/XIOS edition was known as Concurrent PC DOS 3.2. Kathryn Strutynski held the role of product manager during this period.

Concurrent DOS 68K and FlexOS 68K

A partnership initiated with Motorola in 1984 resulted in the development of Concurrent DOS 68K in Austin, Texas, as a successor to CP/M-68K, programmed in C. Francis "Frank" R. Holsworth played a significant role as an architect. Early in 1985, Concurrent DOS 68K version 1.0 was made available for OEM assessment, backed by Motorola’s multi-million dollar investment and targeting their 68000/68010 processors. Initially deployed on Motorola's VME/10 development platform, it was later ported to Compupro systems.

The release history for Concurrent DOS 68K includes:

  • Version 1.0 (1985)
  • Version 1.1
  • Version 1.20 (April 1986)
  • Version 1.21 (1986)

By late 1986, this product line transitioned into FlexOS 68K.

Concurrent DOS 286 and FlexOS 286

Alongside Concurrent DOS 68K, Digital Research unveiled Concurrent DOS 286 in January 1985 through collaboration with Intel. Building on earlier work with MP/M-286 and Concurrent CP/M-286 since 1982, this system was rewritten in C, featuring dynamically loadable device drivers instead of fixed BIOS/XIOS components. Francis "Frank" R. Holsworth was a principal designer.

Tailored for native operation on the Intel 80286 processor’s protected mode, it provided multi-user multitasking with support for 8086 emulation. Although initial prototype chips enabled this functionality, production delays occurred due to Intel revising the processor microcode to enhance emulation performance.

These technical obstacles also affected FlexOS 286 version 1.x—a redesigned variant developed by Digital Research's Flexible Automation Business Unit located in Monterey starting in 1986.

Subsequent updates incorporated support for PC DOS versions 2.x and 3.x.

Notable releases include:

Concurrent DOS XM and Concurrent DOS 386

In 1986, Digital Research transferred its OEM Support Group to the European Development Centre (EDC) located in Hungerford, UK. From version 4.11 onward, this center assumed responsibility for advancing the Concurrent DOS series, including associated products such as DOS Plus.

The Concurrent DOS iterations 5 and 6—known as Concurrent DOS XM (with XM denoting Expanded Memory)—were developed at the Hungerford facility. These versions incorporated bank switching capabilities supporting up to 8 MB of EEMS, allowing a real-mode platform to execute multiple CP/M-86 and DOS applications simultaneously. The system supported up to three users concurrently: one local user and two connected via serial terminals.

In 1987, Concurrent DOS was redesigned as Concurrent DOS 386 to exploit the hardware virtualization features offered by the Intel 80386 processor. This enhancement enabled most DOS programs to operate unaltered within a multiuser context, facilitating concurrent file access and multiuser applications as if each user had an individual networked PC. This approach allowed for cost-efficient multiuser configurations utilizing simple terminals or low-end PCs running terminal emulation software, thereby minimizing dependency on costly workstations and network interface cards. To maintain database consistency in multiuser scenarios, record locking mechanisms were implemented.

Concurrent DOS 386 demanded approximately 200K of conventional memory—considerably more than MS-DOS—and required at least 512K of RAM merely to reach the command prompt. For optimal performance with major applications like Microsoft Word or Multiplan, an additional 1MB beyond the standard 640K base memory was advisable.

The release of Concurrent DOS 6.0 also signified the inception of the DR DOS product family, which subsequently evolved into a distinct line of operating systems.

Notable versions include:

  • DR Concurrent PC DOS XM 5.0 (BDOS 5.0)
  • DR Concurrent DOS XM 5.0 (BDOS 5.0, October 1986)
  • DR Concurrent DOS XM 5.1 (BDOS approximately 5.1, January 1987)
  • DR Concurrent DOS XM 5.2 (BDOS approximately 5.2, September 1987)
  • DR Concurrent DOS XM 6.0 (BDOS 6.0, November 1987), including release 6.01
  • DR Concurrent DOS XM 6.2 (BDOS 6.2), including release 6.21
  • DR Concurrent DOS 386 editions:
    • Version 1.0 (BDOS approximately 5.0, 1987)
    • Version 1.1 (BDOS approximately 5.2, September 1987)
    • Version 2.0 (BDOS 6.0, November 1987), including release 2.01
    • Version 3.0 (BDOS 6.2, December 1988–January 1989), including releases 3.01 and 3.02

Concurrent PC DOS XM version 5.0 provided emulation of IBM PC DOS 2.10, whereas Concurrent DOS XM version 6.0 and Concurrent DOS 386 version 2.0 aligned with IBM PC DOS 3.30 compatibility standards, thereby improving interoperability with widely used software and broadening appeal within multiuser commercial settings.

Reception

In a 1988 review by BYTE, Concurrent DOS 386 was characterized as "substantially compatible" with MS-DOS; notably, Microsoft Word version 3.1 operated successfully while version 4.0 failed due to reliance on undocumented DOS features. The system’s performance scaled inversely with the number of simultaneous applications running. Despite its elevated memory requirements, video input/output operations were reported to be twice as fast compared to standard DOS environments. The publication concluded that although more sophisticated operating systems for the Intel 386 were anticipated soon, Concurrent DOS 386 "is here today and ready to go".

Concurrent Controls Variants

Concurrent Controls, Inc. developed several iterations of Concurrent DOS, such as:

  • CCI Concurrent DOS 386 ranging from version 1.12 (October 1987) up to 3.10 R1 (October 2003)
  • Key releases include version 2.01 (May 1988), the 3.04 edition also known as "CCI Concurrent DOS 4.0" (July 1991), along with multiple updates throughout the late 1990s

Additional variants:

  • Apricot Concurrent DOS 386 version 2.01 (1987) designed for the Apricot Quad with Version Level 4.3

Multiuser DOS

Subsequent releases of Concurrent DOS 386 incorporated functionalities from Digital Research’s PC DOS-compatible DR DOS 5.0, adopting the name "Multiuser DOS" (MDOS) starting with version 5.0 (BDOS 6.5) in 1991.

Multiuser DOS encountered technical constraints that limited its ability to rival LAN solutions built on PC DOS. The system demanded custom device drivers because PC DOS drivers did not support multiuser or multitasking environments, making installation more complex by requiring kernel relinking through the SYSGEN command.

It faced difficulties accommodating typical PC DOS enhancements like network protocol stacks and contemporary peripherals including graphics cards, audio devices, CD-ROM drives, and mice. Although graphical terminals were created to facilitate the use of CGA, EGA, and VGA applications, Multiuser DOS lacked the versatility found in networks consisting of standalone PCs. As hardware costs for PCs decreased, Multiuser DOS lost competitiveness despite its advantages in administration and cost-efficiency. Furthermore, its multi-user licensing model resulted in higher expenses compared to single-user systems and it necessitated specialized drivers unlike single-user multitasking utilities such as Quarterdeck’s DESQview. Unlike MP/M, Multiuser DOS never achieved widespread acceptance for single-user multitasking scenarios.

Following Novell’s acquisition of Digital Research in 1991 and the subsequent discontinuation of Multiuser DOS in 1992, three primary Master VARs—DataPac Australasia, Concurrent Controls, and Intelligent Micro Software—secured source code licenses to independently continue development from 1994 onward.

Documented versions include:

  • DR Multiuser DOS 5.00 (1991), and 5.01
  • Novell DR Multiuser DOS 5.10 (April 1992), followed by 5.11
  • Novell DR Multiuser DOS 5.13 (BDOS 6.6, released in 1992)

All Digital Research and Novell Multiuser DOS editions reported themselves as "IBM PC DOS" version 3.31 to maintain compatibility.

DataPac Australasia

Versions released by DataPac Australasia Pty Limited are:

  • Datapac Multiuser DOS version 5.0
  • Datapac Multiuser DOS version 5.1 (BDOS 6.6)
  • Datapac System Manager version 7.0 (August 22, 1996)

After being acquired by Citrix Systems, Inc. in 1997, Datapac's System Manager product was discontinued shortly thereafter. In 2002, Citrix spun off its Sydney-based division into the Advanced Products Group.

Concurrent Controls

Concurrent Controls, Inc. issued several releases under the CCI Multiuser DOS line:

  • Versions ranging from CCI Multiuser DOS 7.00 through to 7.22, covering releases from R1 (September 1996) up to R18 GOLD (April 21, 2005)

All CCI Multiuser DOS versions present themselves as "IBM PC DOS" version 3.31, which can be modified using the DOSVER utility.

In 1999, Concurrent Controls rebranded as Applica, Inc., later renamed Aplycon Technologies, Inc. in 2002.

IMS Multiuser DOS

Recognized IMS Multiuser DOS iterations consist of:

  • Enhanced Release 5.1 (1992), along with versions 5.11, 5.14, 7.0, and 7.1 (BDOS 6.7, 1994)

Every edition identifies itself as "IBM PC DOS" version 3.31.

REAL/32

In 1994, Intelligent Micro Software Ltd., based in Thatcham, UK, obtained a license from Novell to develop Multiuser DOS and introduced REAL/32 in 1995.

IBM adopted REAL/32 version 7.50 in 1995 for deployment on its 4695 POS systems.

The REAL/32 release timeline includes:

  • Versions 7.50 through 7.54 (1995–1996)
  • Versions 7.60 through 7.63 (1997)
  • Versions 7.70 through 7.74 (1998)
  • Versions 7.80 through 7.83 (1999)
  • Versions 7.90 through 7.92 (1999)
  • ITERA IMS REAL/32 versions 7.93 to 7.94 (2002–2003)
  • Integrated Solutions IMS REAL/32 version 7.95 (circa 2010)

Versions up to 7.74 report themselves as "IBM PC DOS" version 3.31; starting with version 7.80, they identify as version 6.20.

Support for Logical Block Addressing (LBA) and FAT32 was introduced in version 7.90 in the year 1999.

Following IMS’s insolvency filing in April 2002, Itera Ltd., a principal client, acquired the company; Itera was subsequently dissolved in March 2006.

By around 2010, Integrated Solutions of Thatcham, UK, was distributing REAL/32, although the firm later redirected its focus away from software production.


REAL/NG

REAL/NG represented IMS’s effort to create the "Next Generation" iteration of REAL/32, marketed as "REAL/32 for the internet age." It aimed to support a broader spectrum of hardware platforms ranging from standard PCs to x86 multiprocessing servers.

Prominent capabilities highlighted in the 2003 marketing included:

  • Compatibility with Red Hat Linux version 7.3 or newer
  • Full backward compatibility with both DOS and REAL/32
  • Support for up to 65,535 virtual consoles or users
  • Administration and upgrade management via web browser interfaces, both locally and remotely
  • Included TCP/IP terminal emulator compatible with Linux and Windows clients
  • Integrated printing and file sharing services with drive mapping between Linux and REAL/NG servers
  • Advanced hardware support for users alongside multiprocessing enhancements
  • Embedded firewall functionality, performance optimizations, and extended TPA support
  • Competitive pricing per user seat and reduced total cost of ownership
  • Distribution on CD bundled with Red Hat installation packages

The last known version released was "REALNG V1.60-V1.19-V1.12" as of December 2003; by 2005, the realng.com website redirected visitors to IMS’s main portal without referencing REAL/NG, indicating discontinuation.


Application software

Applications developed for this operating system leveraged its multiuser capabilities through specialized function calls, utilizing pre-emptive multitasking to prevent any single poorly designed program from monopolizing CPU resources.

Multiuser DOS remains compatible with contemporary SSL/TLS libraries such as wolfSSL.

Its programming interface supported features including blocking and non-blocking message queues, mutex-protected queues, subprocess threads that operate independently from their parent processes, and efficient pause mechanisms that conserve CPU cycles.

Programs could execute attached to virtual consoles or detached for background operation with optional reattachment later.

Memory management employed a shared memory architecture that separated immutable code segments from modifiable data areas, enabling multiple instances of the same program to share code pages and thereby optimize memory usage.

Software adapted for multitasking avoided inefficient busy-wait loops by invoking API calls to sleep or yield processor time.

Later Concurrent DOS releases introduced Idle Detection technology—monitoring API usage patterns to suspend inactive processes—pioneering power-saving innovations like DR-DOS’s patented Dynamic Idle Detection marketed under BatteryMAX branding.


See also

Further reading

  • DRTIPS.ZIP (1992) authored by Novell Desktop Systems Group, Digital Research/Novell

External links

Related profiles

RREAL/32CCCPM.SYSCCCPMNET.SYSCConcurrent CP/M with Windows
Retrieved from "https://www.alfawiki.org/index.php?title=Concurrent_DOS_386/MGE&oldid=25257"