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CCPMNET.SYS

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Adapted from the English Wikipedia article CCPMNET.SYS, available under CC BY-SA 4.0Updated 9 August 20254 sources
Digital Research
Company typePrivate
IndustrySoftware
Founded1970
FounderGary Kildall
FateAcquired by Novell (1991)
SuccessorNovell (for Multiuser DOS)
Headquarters
Pacific Grove, California
,
United States
ProductsMultiuser DOS, Concurrent CP/M-86, Concurrent DOS, FlexOS

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

Originally created by Digital Research as a progression from Concurrent CP/M-86, Concurrent DOS, and Concurrent DOS 386, the system was later acquired and enhanced by Novell in 1991. Its lineage extends back to Digital Research’s earlier 8-bit operating systems, including 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 prominent value-added resellers (VARs)—DataPac Australasia, Concurrent Controls, and Intelligent Micro Software—secured licenses to independently continue its development. This led to the creation of Datapac Multiuser DOS and System Manager, CCI Multiuser DOS, and IMS Multiuser DOS along with REAL/32.

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 release of CP/M-86 1.0 (utilizing BDOS 2.x) was adapted for the IBM PC in 1982 but failed commercially due to strong competition from IBM’s PC DOS 1.0, which provided comparable features at a lower cost. Both operating systems did not fully exploit the capabilities of the new 16-bit hardware.

In September 1981, an iteration of CP/M's multitasking variant, MP/M-86 2.0, allowed PCs to support multiple simultaneous users through dumb terminals connected via serial ports. This multi-user functionality offered considerable cost advantages over providing individual PCs for each user and supported shared-data applications such as accounting and inventory management before PC networking became prevalent.

In late 1982, CP/M-86 1.1 (BDOS 2.2) and MP/M-86 2.1 were combined into Concurrent CP/M-86 3.0 (BDOS 3.0). Development was overseen by project manager Kathryn Strutynski with design contributions from Francis "Frank" R. Holsworth. Initially designed as a single-user OS with true multitasking capabilities for up to four CP/M-86-compatible programs, it also included multiprocessor support and "virtual screens" to switch between tasks. Subsequent releases extended functionality to support dumb terminals in multiuser configurations. Concurrent CP/M-86 3.1 (BDOS 3.1) was launched on 21 February 1984.

Concurrent CP/M-86 with Windows

In February 1984, Digital Research introduced 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 was developed for LSI-M4, LSI Octopus, and CAL PC systems that integrated 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 running applications on the appropriate processor according to file extension (.COM for 8-bit programs, .CMD for 16-bit). It simulated the CP/M environment for 8-bit applications by translating system calls to operate on the 16-bit processor.

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) that 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 accommodated straightforward DOS applications that refrained from direct hardware interaction—console utilities like PKZIP performed efficiently, surpassing the native ARC archiver; however, software requiring screen control such as WordStar necessitated native CP/M editions.

Up to version 4.1, Concurrent DOS development took place primarily in the United States, while OEM customization and regional adaptations were managed by Digital Research Europe’s OEM Support Group based in Newbury, UK beginning in 1983.

Digital Research marketed Concurrent DOS 4.1 combined with GEM as a competitive alternative to IBM’s TopView in 1985. Concurrent DOS 4.1 (BDOS 4.1) was compatible with PC DOS 2.x and was ported across various hardware platforms; the IBM PC-compatible variant was branded Concurrent PC DOS 4.1.

Concurrent PC DOS

Released in 1984, Concurrent DOS 3.2 (featuring 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 deployed on multiple hardware platforms, with the IBM PC-compatible BIOS/XIOS edition titled Concurrent PC DOS 3.2. The product management role was held by Kathryn Strutynski.

Concurrent DOS 68K and FlexOS 68K

Starting in 1984, a partnership with Motorola resulted in the development of Concurrent DOS 68K at Austin, Texas, serving as the successor to CP/M-68K and written entirely in C. Francis "Frank" R. Holsworth was a principal architect of this project. By early 1985, Concurrent DOS 68K version 1.0 was available for OEM assessment, backed by multimillion-dollar funding from Motorola and targeting their 68000/68010 processors. Initially deployed on Motorola's VME/10 development platform, it was subsequently adapted for Compupro systems. Versions 1.20/1.21 were launched in April 1986 at an approximate price of , aimed at OEM clients. This operating system later evolved into FlexOS 68K by late 1986.

Notable 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

In parallel with Concurrent DOS 68K, Digital Research unveiled Concurrent DOS 286 in collaboration with Intel in January 1985, building upon MP/M-286 and Concurrent CP/M-286 efforts dating back to 1982. Led by architect Frank R. Holsworth, this rewrite utilized C language and introduced a novel design incorporating dynamically loadable device drivers instead of fixed BIOS/XIOS components.

Engineered to operate natively in Intel 80286 mode, it enabled protected-mode multi-user multitasking alongside 8086 emulation. Early prototype processors supported these features; however, production delays occurred due to hardware issues until Intel resolved processor errata through updated stepping levels (E-1 and E-2), which enhanced emulation efficiency via microcode improvements such as LOADALL.

These processor constraints also influenced FlexOS 286 version 1.x—a reengineered offshoot developed by Digital Research's Flexible Automation Business Unit located in Monterey starting in 1986.

Subsequent updates extended compatibility to PC DOS versions 2.x and 3.x.

Key versions 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 formed European Development Centre (EDC) located in Hungerford, UK. This center assumed responsibility for advancing the Concurrent DOS series starting with Concurrent DOS 4.11, as well as associated products such as DOS Plus.

The development of versions 5 and 6 occurred at the Hungerford facility under the name Concurrent DOS XM (where XM denotes Expanded Memory). These editions facilitated bank switching up to 8 MB of EEMS, allowing a real-mode platform to execute multiple CP/M-86 and DOS programs simultaneously. They supported up to three users concurrently—one local and two through serial terminal connections.

By 1987, Concurrent DOS underwent a complete rewrite resulting in Concurrent DOS 386,[1] which maintained the traditional XIOS & BDOS framework. Tailored for Intel 80386 and subsequent processors, it utilized hardware virtualization to run most DOS software without modification, even on terminal devices. This operating system enabled multiuser file access concurrently, permitting applications designed for multiple users to function as if each user operated an individual PC connected via a network server. Such architecture reduced expenses by supporting several users on simple terminals or low-end PCs without requiring costly workstations or network interface cards. It incorporated genuine multiuser features including record locking to safeguard shared databases.

Concurrent DOS 386 demanded approximately 200K of conventional memory—substantially more than MS-DOS—and recommended a minimum of 1.5MB RAM for efficient operation of multiple large programs like Microsoft Word or Multiplan.[2]

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

Notable releases 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 5.1?, January 1987)
  • DR Concurrent DOS XM 5.2 (BDOS 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 revision 6.21
  • DR Concurrent DOS 386 1.0 (BDOS ~5.0, 1987)
  • DR Concurrent DOS 386 1.1 (BDOS ~5.2, September 1987)
  • DR Concurrent DOS 386 2.0 (BDOS 6.0, November 1987), with version 2.01
  • DR Concurrent DOS 386 3.0 (BDOS 6.2, late 1988–1989), including versions 3.01 and 3.02

The Concurrent PC DOS XM 5.0 version emulated IBM PC DOS version 2.10,[3] whereas both Concurrent DOS XM 6.0 and Concurrent DOS 386 version 2.0 were compatible with IBM PC DOS version 3.30.[4]

Reception

In a review from BYTE magazine in 1988, Concurrent DOS 386 was characterized as "largely compatible" with MS-DOS; for instance, Microsoft Word version 3.1 operated correctly while version 4.0 did not due to reliance on undocumented DOS features. System performance declined proportionally with the number of concurrently running applications. Despite its greater memory requirements, BYTE observed that video input/output was twice as fast compared to standard DOS systems, concluding that although more sophisticated operating systems for the Intel 386 were anticipated soon, Concurrent DOS 386 "is currently available and fully functional."

Concurrent Controls Variants

Concurrent Controls, Inc. developed multiple iterations of Concurrent DOS, which include:

  • CCI Concurrent DOS 386 1.12 (October 1987)
  • CCI Concurrent DOS 386 2.01 (May 1988)
  • CCI Concurrent DOS 386 3.01 (March 1989)
  • CCI Concurrent DOS 386 3.02 (April 1990)
  • CCI Concurrent DOS 386 3.03 (March 1991)
  • CCI Concurrent DOS 386 3.04, also known as "CCI Concurrent DOS 4.0" (July 1991)
  • CCI Concurrent DOS versions 3.05 R1 through R11 (1992–August 1993)
  • CCI Concurrent DOS versions 3.06 R1 through R7 (December 1993–July 1994)
  • CCI Concurrent DOS versions 3.07 R1 through R7 (March 1995–June 1998)
  • CCI Concurrent DOS 3.08
  • CCI Concurrent DOS 3.10 R1 (October 2003)

Additionally, Apricot Concurrent DOS 386 version 2.01 (1987) was released for the Apricot Quad Version Level 4.3 platform.

Multiuser DOS Evolution

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

Multiuser DOS encountered technical challenges that limited its ability to compete with LANs based on PC DOS. It demanded custom device drivers because standard PC DOS drivers lacked multiuser and multitasking capabilities, making installation more complex by requiring kernel relinking through SYSGEN. Furthermore, it had difficulty supporting typical PC DOS add-ons such as network protocol stacks and newer hardware peripherals including graphics cards, sound devices, CD-ROM drives, and pointing devices.

Though some of these issues were mitigated—for instance, graphical terminal support allowed use of CGA, EGA, and VGA software—Multiuser DOS remained less adaptable than networks composed of standalone PCs. As the cost of personal computers declined, the management and total cost of ownership benefits offered by Multiuser DOS lessened significantly. Its price point was higher than single-user systems and it required specialized drivers, unlike multitasking enhancements like Quarterdeck’s DESQview. Unlike MP/M, Multiuser DOS failed to gain traction as a single-user multitasking solution.

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

Documented releases include:

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

All these editions reported themselves as "IBM PC DOS" version 3.31 to maintain compatibility.

DataPac Australasia

DataPac Australasia Pty Limited produced several known versions:

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

After Citrix Systems, Inc.’s acquisition of DataPac in 1997, System Manager was phased out shortly thereafter. In 2002, the Sydney-based division was spun off into Citrix’s Advanced Products Group.

Concurrent Controls Developments

Concurrent Controls, Inc. issued multiple Multiuser DOS variants including:

  • Versions: CCI Multiuser DOS 7.00, 7.10, 7.21, and 7.22
  • GOLD editions ranging from Release R1 through R18 produced between 1996 and 2005

Each CCI Multiuser DOS release identifies as "IBM PC DOS" version 3.31; this identification can be altered using the Multiuser DOS utility.

In the year 1999, Concurrent Controls rebranded to Applica, Inc., followed by a name change to Aplycon Technologies, Inc., in 2002.


IMS Multiuser DOS

Versions of IMS Multiuser DOS include:

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

All versions identify themselves as "IBM PC DOS" version 3.31.

REAL/32

In 1994, Intelligent Micro Software Ltd., based in Thatcham, UK, obtained the rights from Novell to further develop Multiuser DOS, subsequently rebranding it as REAL/32 in 1995.

IBM incorporated REAL/32 version 7.50 into its 4695 POS terminal offerings in the same year.

REAL/32 releases span:

  • IMS REAL/32 editions beginning with 7.50 (BDOS 6.8, 1995) through to 7.95 (under Integrated Solutions, circa 2010)
  • Versions up to 7.74 report as "IBM PC DOS" version 3.31; from version 7.80 onwards, the reported version is 6.20
  • Introduction of LBA and FAT32 support with REAL/32 version 7.90 in 1999

Following insolvency proceedings in April 2002, Intelligent Micro Software Ltd was acquired by Itera Ltd., a client company led by Barry Quittenton, which later dissolved in March 2006.

By around 2010, Integrated Solutions Ltd of Thatcham, UK supplied REAL/32; this firm eventually transitioned its business focus to construction services at the same location.

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." It was engineered to operate across a wide spectrum of hardware platforms, from personal computers to x86 multiprocessor servers.

Highlighted features circa 2003 included:

  • Support for Red Hat Linux version 7.3 and subsequent releases
  • Backward compatibility with existing DOS and REAL/32 applications
  • Capability to handle up to 65,535 virtual consoles, each corresponding to an individual user session
  • Administration accessible through web browsers locally or remotely without requiring Linux proficiency
  • Integrated TCP/IP terminal emulator compatible with both Linux and Windows clients
  • Native print and file sharing functionalities alongside drive mapping between Linux and REAL/NG servers
  • Improved hardware compatibility and multiprocessor support
  • Embedded firewall protection
  • Enhanced performance with significantly expanded transient program area (TPA)
  • Cost-effective per-user licensing and lowered total cost of ownership
  • Distribution bundled on CD alongside Red Hat installation media

The final known version was release 1.60 around December 2003; by 2005, REAL/NG had been removed from IMS’s website in favor of renewed emphasis on REAL/32.

Application software

Applications developed for this environment utilized APIs tailored for multiuser systems featuring pre-emptive multitasking, thereby preventing any single poorly designed program from dominating CPU time.

Multiuser DOS maintains compatibility with SSL/TLS libraries such as wolfSSL, underscoring its continued relevance in secure communications.

The API supported mechanisms including blocking and non-blocking message queues, mutual-exclusion queues, subprocess threads operating independently of parent processes, and efficient pause routines that avoided the CPU waste typical of idle loops found in single-user operating systems.

Programs could attach directly to virtual consoles or execute detached in the background as independent processes.

Memory management employed a shared memory architecture separating code from data sections; since code segments contained no writable data, they could be shared among multiple instances of the same application, optimizing overall memory utilization.

Applications adapted for multitasking avoided endless polling loops awaiting user input by invoking API calls that placed them into a sleep state, thereby conserving processor resources.

Later iterations of Concurrent DOS introduced Idle Detection technology that suspended inactive processes to free CPU cycles—a concept that evolved into the patented Dynamic Idle Detection power management system marketed under the name BatteryMAX.

See also

Further reading

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

External links

  1. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named IW_1987_MDOS386
  2. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named lane198807
  3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named 1986_CDOSXM
  4. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named DRI_1988_CDOS

Related profiles

CCCPM.SYSRREAL/32CConcurrent CP/M with WindowsCConcurrent CP/M-86 with Windows
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