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REAL/NG

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Adapted from the English Wikipedia article REAL/NG, available under CC BY-SA 4.0Updated 9 August 2025
Digital Research
IndustryComputer software
Founded1974; 52 years ago (1974)
FounderGary Kildall
FateAcquired by Novell in 1991; development ceased in 1992
SuccessorNovell (for Multiuser DOS)
Headquarters
Pacific Grove, California
,
United States
ProductsMultiuser DOS, Concurrent CP/M-86, Concurrent DOS, FlexOS

Multiuser DOS represents a real-time, multi-user, multitasking operating system designed for IBM PC-compatible microcomputers.

Originally created by Digital Research as an advancement of Concurrent CP/M-86, Concurrent DOS, and Concurrent DOS 386, the system was acquired and further enhanced by Novell in 1991. Its lineage extends back to Digital Research's earlier 8-bit systems, including CP/M and MP/M, as well as the 16-bit single-tasking CP/M-86.

Following Novell's cessation of Multiuser DOS development in 1992, three principal value-added resellers (VARs)—DataPac Australasia, Concurrent Controls, and Intelligent Micro Software—assumed independent development responsibilities. They released Datapac Multiuser DOS and System Manager, CCI Multiuser DOS, and IMS Multiuser DOS along with REAL/32, respectively.

The 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 because IBM's PC DOS 1.0 offered comparable features at a lower cost. Neither operating system fully utilized the potential of the then-new 16-bit architecture.

This was complemented by the release of MP/M-86 2.0 in September 1981, which converted a PC into a multi-user platform supporting several simultaneous users through dumb terminals connected via serial ports. This configuration provided substantial cost efficiency over deploying multiple PCs and facilitated shared-data applications such as accounting or inventory management prior to the widespread adoption of PC networking.

In late 1982, CP/M-86 1.1 (BDOS 2.2) and MP/M-86 2.1 were integrated into Concurrent CP/M-86 3.0 (CCP/M-86) featuring BDOS 3.0. The project was managed by Kathryn Strutynski with design led by Francis "Frank" R. Holsworth. Initially developed as a single-user OS with genuine multitasking capabilities for up to four CP/M-86-compatible programs, it could also be configured for multi-processor environments and introduced "virtual screens" allowing users to switch between running applications. Subsequent versions incorporated support for dumb terminals enabling multiuser functionality. Concurrent CP/M-86 3.1 (BDOS 3.1) was released on February 21, 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 incorporated windowing features.

Concurrent CP/M-86/80

This version targeted systems such as the LSI-M4, LSI Octopus, and CAL PC computers, which combined both 16-bit and 8-bit processors to take advantage of the wider availability and performance benefits of 8-bit software. Concurrent CP/M-86/80 allowed execution of both CP/M (8-bit) and CP/M-86 (16-bit) applications by directing commands to the appropriate processor based on file extensions (.COM for 8-bit programs, .CMD for 16-bit). It simulated the CP/M environment for 8-bit software by converting system calls into equivalents handled by the 16-bit processor running CP/M-86.

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), which offered fundamental compatibility with PC DOS 1.1. This was showcased at COMDEX in December 1983 and released to hardware manufacturers in March 1984 as Concurrent DOS 3.1 (CDOS with BDOS 3.1). It enabled basic DOS programs that did not directly access hardware to operate—for instance, PKZIP ran smoothly and provided more capabilities than the native CP/M ARC archiver. Nevertheless, software requiring direct screen control, such as WordStar for DOS, necessitated versions native to Concurrent CP/M.

While the core development of Concurrent DOS versions 3.1 through 4.1 took place within the United States, OEM customization and localization efforts were handled by Digital Research Europe’s OEM Support Group based in Newbury, UK starting in 1983.

Digital Research marketed Concurrent DOS 4.1 bundled with the Graphics Environment Manager (GEM) as a competitor to IBM's TopView in 1985. Concurrent DOS 4.1 (BDOS 4.1) provided compatibility with PC DOS 2.x on multiple hardware platforms; its IBM PC-compatible BIOS/XIOS variant was titled Concurrent PC DOS 4.1.

Concurrent PC DOS

Released in 1984, Concurrent DOS 3.2 (BDOS 3.2) supported applications designed for CP/M-86 1.x, Concurrent CP/M-86 3.x, and PC DOS 2.0 environments. It was distributed across various hardware systems; the IBM PC-compatible BIOS/XIOS edition carried the name Concurrent PC DOS 3.2. Product management was overseen by Kathryn Strutynski.

Concurrent DOS 68K and FlexOS 68K

Beginning in 1984, Digital Research partnered with Motorola to develop Concurrent DOS 68K in Austin, Texas, as a successor to CP/M-68K, written entirely in C. Francis "Frank" R. Holsworth played a leading role in its architecture. By early 1985, Concurrent DOS 68K version 1.0 was available for OEM evaluation; Motorola funded this project with a multimillion-dollar investment targeting their 68000 and 68010 processors. Initially deployed on Motorola VME/10 development platforms, it was subsequently ported to additional systems. Versions 1.20 and 1.21 were released in April and later in 1986 respectively, offered commercially to OEMs before evolving into FlexOS 68K by the end of 1986.

Documented releases include:

  • Concurrent DOS 68K 1.0 (1985)
  • Concurrent DOS 68K 1.1
  • Concurrent DOS 68K 1.20 (April 1986)
  • Concurrent DOS 68K 1.21 (1986)

Concurrent DOS 286 and FlexOS 286

Alongside Concurrent DOS 68K development, Digital Research introduced Concurrent DOS 286 in collaboration with Intel in January 1985, building upon MP/M-286 and prior work on Concurrent CP/M-286 dating back to 1982. This was a comprehensive rewrite coded in C that incorporated dynamically loadable device drivers replacing fixed BIOS/XIOS components. Frank Holsworth again contributed as a principal architect.

Designed specifically for native 80286 mode operation, it supported protected-mode multitasking with multi-user capabilities while also accommodating 8086 emulation mode. Early prototype processors enabled this functionality; however, production-level CPU issues postponed the release from May until Intel produced revised chips resolving emulation difficulties.

After rigorous testing of E-1 stepping samples, Intel implemented microcode enhancements in the E-2 stepping that improved emulation via LOADALL. These constraints also impacted FlexOS 286, a reengineered variant developed by Digital Research’s Flexible Automation Business Unit starting in 1986.

Subsequent editions improved support for PC DOS versions 2.x and 3.x.

Known releases include:

  • Concurrent DOS 286 1.0 (1985)
  • Concurrent DOS 286 1.1 (January 7, 1986)
  • Concurrent DOS 286 1.2 (1986)
  • FlexOS 286 1.3 (November 1986)
  • FlexOS 286 1.31 (May 1987)

Concurrent DOS XM and Concurrent DOS 386

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

Concurrent DOS versions 5 and 6, developed at Hungerford and known as Concurrent DOS XM (where XM denotes Expanded Memory), introduced bank switching capabilities for up to 8 MB of EEMS. This innovation allowed a real-mode environment to execute multiple CP/M-86 and DOS applications simultaneously while supporting up to three users—one local and two connected via serial terminals.

In 1987, the operating system was reengineered into Concurrent DOS 386, preserving the traditional XIOS and BDOS framework. Designed for Intel 80386 and subsequent processors, it utilized hardware virtualization to run most DOS software without modification, including on terminal devices. The system enabled concurrent multiuser file access, allowing applications to function as if each user had a dedicated PC linked to a network server. This architecture facilitated multiple users operating on inexpensive terminals or PCs with terminal emulation software, eliminating the need for costly workstations or network interface cards. It was a genuine multiuser platform featuring record locking to maintain database consistency.

Concurrent DOS 386 demanded approximately 200K of conventional memory—considerably more than MS-DOS—and required at least 512K of RAM merely to display the command prompt. Around 1MB beyond the standard 640K memory limit was necessary to run three substantial programs such as Microsoft Word or Multiplan concurrently.

The release of Concurrent DOS 6.0 also marked the foundation of the DR DOS lineage, which evolved from this version.

Recognized editions comprise:

  • 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 update 6.01
  • DR Concurrent DOS XM 6.2 (BDOS 6.2), including update 6.21
  • DR Concurrent DOS 386 releases from version 1.0 (1987) through 3.02 (1989), with BDOS versions ranging from about 5.0 to 6.2

Concurrent PC DOS XM 5.0 provided emulation of IBM PC DOS version 2.10, while both Concurrent DOS XM 6.0 and Concurrent DOS 386 version 2.0 maintained compatibility with IBM PC DOS version 3.30.

Reception

In a 1988 review by BYTE, Concurrent DOS 386 was characterized as "largely compatible" with MS-DOS; for instance, Microsoft Word version 3.1 operated correctly whereas version 4.0 failed due to undocumented system calls in DOS. Performance degraded proportionally with the number of active applications; however, video input/output throughput was reported to be twice that of standard DOS despite increased memory demands. The publication concluded that although more sophisticated operating systems for the 386 processor were forthcoming, Concurrent DOS 386 was available immediately and ready for deployment.

Adaptations

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

  • CCI Concurrent DOS 386 1.12 (October 1987)
  • CCI Concurrent DOS 386 2.01 (May 1988)
  • CCI Concurrent DOS 386 3.01 (March 1989)
  • Versions extending to CCI Concurrent DOS 386 3.07 R7 (June 1998)
  • CCI Concurrent DOS 3.10 R1 (October 2003)

Additional variants include Apricot Concurrent DOS 386 2.01 (1987), designed specifically for the Apricot Quad system.

Multiuser DOS

Subsequent releases of Concurrent DOS 386 integrated elements from Digital Research’s PC DOS-compatible DR DOS 5.0, prompting a rebranding to "Multiuser DOS" (MDOS) beginning with version 5.0 (BDOS 6.5) in 1991.

Multiuser DOS encountered technical limitations that hindered its ability to compete effectively with PC DOS-based local area networks. It demanded specialized device drivers for standard hardware because PC DOS drivers lacked support for multiuser and multitasking environments, which complicated setup and required kernel relinking through SYSGEN. Furthermore, it had difficulty accommodating PC DOS enhancements such as network protocol stacks and newer hardware peripherals including graphics adapters, sound devices, CD-ROM drives, and mice. Although some challenges were partially resolved—for example, graphical terminal support allowed the use of CGA, EGA, and VGA applications—its adaptability remained inferior to networks composed of individual PCs.

While Multiuser DOS involved greater expense than single-user systems and necessitated unique drivers, it provided advantages in system management and reduced overall ownership costs. Nevertheless, it did not achieve widespread acceptance for single-user multitasking when compared to alternatives like Quarterdeck’s DESQview.

Following Novell’s acquisition of Digital Research in 1991 and the subsequent discontinuation of Multiuser DOS in 1992, key value-added resellers such as DataPac Australasia, Concurrent Controls, and Intelligent Micro Software secured licenses to the source code to pursue independent development starting in 1994.

Documented releases include:

  • DR Multiuser DOS 5.00 (1991), 5.01
  • Novell DR Multiuser DOS 5.10 (April 1992), 5.11
  • Novell DR Multiuser DOS 5.13 (BDOS 6.6, 1992)

Every release identified itself as "IBM PC DOS" version 3.31.

DataPac Australasia

DataPac Australasia Pty Limited produced the following versions:

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

After Citrix Systems, Inc. acquired DataPac in 1997, the System Manager product was discontinued shortly thereafter. In 2002, the Sydney-based division was reorganized into Citrix’s Advanced Products Group.

Concurrent Controls

Concurrent Controls, Inc. issued several versions of CCI Multiuser DOS:

  • CCI Multiuser DOS releases ranging from version 7.00 through to 7.22, including R1 to R18 GOLD updates spanning from 1996 until 2005

All CCI Multiuser DOS editions report their identity as "IBM PC DOS" version 3.31; this can be modified using the DOSVER utility.

In 1999, Concurrent Controls changed its name to Applica, Inc., and later in 2002 Applica Technology was renamed Aplycon Technologies, Inc.

IMS Multiuser DOS

Notable versions of IMS Multiuser DOS include:

  • IMS Multiuser DOS Enhanced Release 5.1 (1992)
  • IMS Multiuser DOS releases 5.11 and 5.14
  • IMS Multiuser DOS versions 7.0 and 7.1 (BDOS 6.7, 1994)

All these versions identify themselves 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 continue development of Multiuser DOS, subsequently rebranding it as REAL/32 in 1995.

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

The REAL/32 product line includes the following releases:

  • Versions 7.50 through 7.54 (BDOS versions 6.8 to 6.9; mid-1990s)
  • Versions 7.60 to 7.63 (released in 1997)
  • Versions 7.70 to 7.74 (released in 1998)
  • Versions 7.80 to 7.83 (BDOS 6.10; up to early 1999)
  • Versions 7.90 to 7.92 (released in 1999)
  • ITERA IMS REAL/32 updates up to version 7.94 (2003)
  • Integrated Solutions IMS REAL/32 version 7.95 (circa 2010)

Up through version 7.74, the system reports itself as "IBM PC DOS" version 3.31; starting with version 7.80, this changes to version 6.20.

Support for Logical Block Addressing (LBA) and FAT32 file systems was introduced with REAL/32 release 7.90 in 1999.

In April of 2002, Intelligent Micro Software Ltd entered insolvency proceedings and was subsequently acquired by Itera Ltd., which itself was dissolved in March of 2006.

By the year 2010, Integrated Solutions of Thatcham, UK was distributing REAL/32, although the company later transitioned away from software development activities.


REAL/NG

REAL/NG represented IMS's initiative to create a "Next Generation" iteration of REAL/32, marketed as "REAL/32 for the internet age." This platform aimed to support a diverse hardware spectrum ranging from personal computers to x86-based multi-processor servers.

Key features promoted in the year 2003 included:

  • Compatibility with Red Hat Linux version 7.3 or higher
  • Backward compatibility with existing DOS and REAL/32 applications
  • Capacity to handle up to 65,535 virtual consoles, each corresponding to an individual user
  • Administration and configuration accessible via web browser interfaces, both locally and remotely
  • Integrated TCP/IP terminal emulator available for licensed users on Linux and Windows platforms
  • Native print and file sharing capabilities along with drive mapping between Linux and REAL/NG servers
  • Improved hardware support for users and enhanced multi-processor functionality
  • Built-in firewall protection, performance optimizations, and expanded transient program area (TPA)
  • Competitive cost per user seat alongside reduced total cost of ownership
  • Distribution provided on CD bundled with Red Hat installation media

The final documented release, REALNG versions V1.60-V1.19-V1.12, became available by December of 2003; by 2005, the realng.com domain redirected to IMS’s primary website, which no longer referenced REAL/NG and concentrated exclusively on REAL/32.


Application software

Applications designed for this environment exploited its multiuser architecture through APIs tailored for pre-emptive multitasking, ensuring that faulty or poorly designed programs could not monopolize CPU resources.

Multiuser DOS maintains compatibility with contemporary SSL/TLS libraries such as wolfSSL.

The API framework supported blocking and non-blocking message queues, mutual-exclusion queues, and subprocess threads capable of running independently from their parent processes.

Programs could either operate attached to virtual consoles or detach themselves to run as background services, reconnecting when necessary.

Memory management employed a shared memory architecture where code segments were separated from data; code areas were immutable and sharable among processes executing the same application, thereby optimizing memory utilization.

Unlike single-task operating systems that depended on inefficient busy-wait loops during idle periods, Concurrent DOS introduced API calls allowing processes to "sleep," conserving processor cycles.

Later kernel versions incorporated Idle Detection mechanisms that suspended inactive processes to enhance multitasking efficiency.

This approach culminated in the patented DR-DOS Dynamic Idle Detection power management technology (marketed under the name BatteryMAX), invented in 1989 by Roger Alan Gross and John P. Constant.

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
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