View source for Multiuser DOS

{{Short description|Family of CP/M- and DOS-compatible multi-user multi-tasking operating systems}}
{{Use dmy dates|date=April 2019|cs1-dates=y}}
{{Use list-defined references|date=December 2021}}
{{Infobox OS 
| name                   = Multiuser DOS
| logo                   = 
| screenshot             = Novell DR Multiuser DOS Release 5.1 720x400.png
| caption                = Novell DR Multiuser DOS Release 5.1
| developer              = [[Digital Research]], [[Novell]]
| source_model           = [[Closed source]]
| kernel_type            = [[Monolithic kernel]]
| supported_platforms    = [[x86]], [[Motorola 68000|68000]]
| ui                     = [[Command-line interface]] ([[COMMAND.COM]])
| family                 = [[CP/M]]
| released               = 
| latest_release_version = 7.22 R18
| latest_release_date    = {{Start date and age|2005|04|21|df=yes}} (REAL/32: 7.95<!-- somewhen between 2006 and 2010 -->)
| latest_test_version    = 
| latest_test_date       = 
| marketing_target       = 
| programmed_in          = 
| prog_language          = 
| language               = [[English language|English]]
| updatemodel            = Re-installation
| package_manager        = None
| working_state          = Discontinued
| license                = [[Proprietary software|Proprietary]]
| discontinued           = yes
| website                = Various (see notes)
}}
'''Multiuser DOS''' is a [[Real-time operating system|real-time]] multi-user multi-tasking [[operating system]] for [[IBM Personal Computer|IBM PC]]-compatible microcomputers.

An evolution of the older '''Concurrent CP/M-86''', '''Concurrent DOS''' and '''Concurrent DOS 386''' operating systems, it was originally developed by [[Digital Research]] and acquired and further developed by [[Novell]] in 1991.<ref name="Scott_1991"/><ref name="BW_1991"/><ref name="Allchin_1992"/> Its ancestry lies in the earlier Digital Research [[8-bit]] operating systems [[CP/M]] and [[MP/M]], and the [[16-bit]] single-tasking [[CP/M-86]] which evolved from CP/M.

When Novell abandoned Multiuser DOS in 1992, the three master [[value-added reseller]]s (VARs) DataPac Australasia, [[Concurrent Controls]]<ref name="Barney_1994_CCI"/> and [[Intelligent Micro Software]]<ref name="Pontin_1995_IMS"/> were allowed to take over and continued independent development into Datapac Multiuser DOS and System Manager, CCI Multiuser DOS, and IMS Multiuser DOS and REAL/32.<ref name="Pontin_1995_IMS"/>

The [[FlexOS]] line, which evolved from [[Concurrent DOS 286]] and [[Concurrent DOS 68K]], was sold off to [[Integrated Systems Inc.|Integrated Systems]], Inc. (ISI) in July 1994.

=={{anchor|CCP/M-86}}Concurrent CP/M-86==
{{See also|MP/M#MP/M-86{{!}}MP/M-86}}
<!-- This section may be linked to from inside or outside this article. Do not rename without keeping in sync. -->

The initial version of [[CP/M-86 1.0]] (with BDOS 2.x) was adapted and became available to the [[IBM PC]] in 1982.<!-- it was already available for non-PC platforms in 1981, possibly 1980. --> It was commercially unsuccessful as [[IBM]]'s [[PC&nbsp;DOS 1.0]] offered much the same facilities for a considerably lower price. Neither PC&nbsp;DOS nor CP/M-86 could fully exploit the power and capabilities of the new 16-bit machine.

It was soon supplemented by an implementation of CP/M's multitasking 'big brother', [[MP/M-86 2.0]], since September 1981. This turned a PC into a multiuser machine capable of supporting multiple [[concurrent user]]s using [[dumb terminal]]s attached by [[serial port]]s. The environment presented to each user made it seem as if they had the entire computer to themselves. Since terminals cost a fraction of the then-substantial price of a complete PC, this offered considerable cost savings, as well as facilitating multi-user shared-data applications such as accounts or stock control in a time when PC networks were rare, very expensive and difficult to implement.

[[CP/M-86 1.1]] (with [[BDOS]] 2.2) and MP/M-86 2.1 were merged to create Concurrent CP/M-86 3.0 (also known as CCP/M-86) with BDOS 3.0 in late 1982.<ref name="Kildall_1982_8-bit"/> [[Kathryn Strutynski]], the project manager for CP/M-86, was also the project manager for Concurrent CP/M-86. One of its designers was Francis "Frank" R. Holsworth.<ref name="Wein_2002"/><ref name="Holsworth_2006"/> Initially, this was a single-user operating system supporting true multi-tasking of up to four (in its default configuration) CP/M-86 compatible programs. Like its predecessors it could be configured for [[multi-processor]] support (see e.g. Concurrent CP/M-86/80) and also added "virtual screens" letting an operator switch between multiple interacting programs.<ref name="Kildall_1982_8-bit"/> Later versions supported dumb terminals connected to the CP/M-86 machine as multiuser systems. Concurrent CP/M-86 3.1 (BDOS 3.1) shipped on 21 February 1984.<ref name="DRI_1984_CCPM31"/>

===Adaptations===

===={{anchor|CCP/M-86 with Windows}}Concurrent CP/M-86 with Windows====
In February 1984 Digital Research also offered a version of Concurrent CP/M-86 with windowing capabilities named '''Concurrent CP/M with Windows for the IBM Personal Computer and Personal Computer XT'''.<ref name="CCPM_1984"/>

===={{anchor|CCP/M-86/80}}Concurrent CP/M-86/80====
{{See also|CP/M-86/80|CP/M 8-16|MP/M 8-16}}
This was an adaptation of Concurrent CP/M-86 for the LSI-M4, LSI Octopus<ref name="LSI_Octopus"/> and CAL PC computers. These machines had both 16-bit and 8-bit processors, because in the early days of 16-bit personal computing, 8-bit software was more available and often ran faster than the corresponding 16-bit software. Concurrent CP/M-86/80 allowed users to run both CP/M (8-bit) and CP/M-86 (16-bit) applications. When a command was entered, the operating system ran the corresponding application on either the 8-bit or the 16-bit processor, depending on whether the executable file had a [[.COM (file extension)|.COM]] or [[CMD file (CP/M)|.CMD]] extension. It emulated a CP/M environment for 8-bit programs by translating CP/M [[system call]]s into CP/M-86 system calls, which were then executed by the 16-bit processor.<ref name="Kildall_1982_8-bit"/>

=={{anchor|PCMODE|CDOS}}Concurrent DOS==
<!-- This section may be linked to from inside or outside this article. Do not rename without keeping in sync. -->

In August 1983, Bruce Skidmore, Raymond D. Pedrizetti, Dave Brown and Gordon Edmonds teamed up to create PC-MODE,<ref name="DRI_1984_PCMODE"/> an optional module for Concurrent CP/M-86 3.1<ref name="DRI_1984_CCPM31b"/><ref name="DRI_1984_MicroNotes1"/> (with BDOS 3.1) to provide basic compatibility with [[PC DOS 1.1]] (and [[MS-DOS 1.1]]).<ref name="DRI_1984_MicroNotes1"/><!-- However, DRI always targetted PC DOS compatibility, not MS-DOS compatibility and the emulator reports itself with OEM=IBM, not MS. --> This was shown publicly at [[COMDEX]] in December 1983<ref name="DRI_1984_PCMODE"/> and shipped in March 1984 as Concurrent DOS 3.1 (a.k.a. CDOS with BDOS 3.1) to hardware vendors.<ref name="DRI_1984_CDOS31"/><ref name="DRI_1984_MicroNotes2"/> Simple DOS applications, which did not directly access the screen or other hardware, could be run. For example, although a console program such as [[PKZIP]] worked perfectly and offered more facilities than the CP/M-native [[ARC (file format)|ARC]] archiver, applications which performed screen manipulations, such as the [[WordStar]] [[word processor]] for DOS, would not, and native Concurrent CP/M (or CP/M-86) versions were required.

While Concurrent DOS 3.1 up to 4.1 had been developed in the US, OEM adaptations and localizations were carried out by [[DR Europe]]'s OEM Support Group in [[Newbury, Berkshire|Newbury]], UK,<ref name="DRI_1984_MicroNotes3"/> since 1983.<!-- possibly late 1982 already? -->

Digital Research positioned [[Concurrent DOS 4.1]] with [[Graphics Environment Manager|GEM]] as alternative for [[IBM]]'s [[TopView]] in 1985.<ref name="CW_1985_CDOS41"/><!-- Concurrent DOS 4.1 (with BDOS 4.1) in 198?4 was compatible with PC DOS 2.x and was available for many different hardware platforms, the version with an IBM PC compatible [[BIOS]]/[[XIOS]] was named Concurrent PC DOS 4.1. -->

==={{anchor|CDOS86|CPCDOS|CPCDOS3.2|CPCDOS4.1|CPCDOS4.11}}Concurrent PC DOS===
Concurrent DOS 3.2 (with BDOS 3.2) in 1984 was compatible with applications for CP/M-86 1.x, Concurrent CP/M-86 3.x and PC DOS 2.0.<!-- July 1984 ref specifies CPCDOS without version number, but mentions PC DOS 2.0 compatibility --><ref name="DRI_1984_MicroNotes3"/> It was available for many different hardware platforms. The version with an IBM–PC-compatible BIOS/XIOS was named Concurrent PC DOS 3.2. Kathryn Strutynski was the product manager for Concurrent PC DOS.

==={{anchor|CDOS68K}}Concurrent DOS 68K and FlexOS 68K===
Efforts being part of a cooperation with [[Motorola]] since 1984<ref name="Gallant_1984"/><ref name="DRI_1984_MicroNotes1"/> led to the development of Concurrent DOS 68K in [[Austin, Texas|Austin]], Texas, as a successor to [[CP/M-68K]] written in [[C language|C]]. One of its main architects was Francis "Frank" R. Holsworth<!-- born 19??-09-04 https://amaus.net/static/S100/software/DRI/Digital%20Dialogue/03x04%20198408%20Digital%20Dialogue.pdf --> (known by his initials, FRH).<ref name="Wein_2002"/><ref name="Holsworth_2006"/> Concurrent DOS 68K 1.0 became available for OEM evaluation in early 1985<!-- possibly even late 1984 -->.<ref name="Knox_1986_CDOS68K"/><ref name="Knox_1987_DRI"/> The effort received considerable funding worth several million dollars from Motorola,<ref name="Knox_1986_CDOS68K"/> and was designed for their [[68000]]/[[68010]] processors. Like the earlier<!-- 1984 --> [[GEMDOS]] system for 68000 processors it initially ran on the Motorola [[VME board|VME]]/10 development system<!-- but was also adapted to Compupro systems -->.<ref name="DRI_1984_MicroNotes1"/> Concurrent DOS 68K 1.20/1.21 was available in April 1986,<ref name="DRI_1986_CDOS68K-1"/><ref name="DRI_1986_CDOS68K-2"/><ref name="DRI_1986_CDOS68K-3"/> offered for about {{val|200000|u=dollars}} to OEMs.<ref name="Knox_1986_CDOS68K"/> This system evolved into [[FlexOS 68K]] in late 1986.

Known versions include:

* Concurrent DOS 68K 1.0 (1985)<ref name="Knox_1986_CDOS68K"/>
* Concurrent DOS 68K 1.1<!-- mentioned in VMCONFIG.C --><ref name="DRI_1986_CDOS68K-2"/>
* Concurrent DOS 68K 1.20 (April 1986,<ref name="DRI_1986_CDOS68K-1"/><ref name="DRI_1986_CDOS68K-2"/><ref name="DRI_1986_CDOS68K-3"/> 1986-05-27<!-- mentioned in VMCONFIG.C --><ref name="DRI_1986_CDOS68K-2"/>)
* Concurrent DOS 68K 1.21 (1986)<ref name="DRI_1986_CDOS68K-1"/><ref name="DRI_1986_CDOS68K-2"/><ref name="DRI_1986_CDOS68K-3"/>

==={{anchor|CCPM286|CDOS286|FlexOS}}Concurrent DOS 286 and FlexOS 286===
In parallel to the Concurrent DOS 68K effort,<ref name="Knox_1986_CDOS68K"/> Digital Research also previewed Concurrent DOS 286<ref name="BYTE_1985_CDOS286"/> in cooperation with [[Intel]] in January 1985. This was based on [[MP/M-286]] and Concurrent CP/M-286, on which Digital Research had worked since 1982.<ref name="Swaine_1982_MPM286"/><ref name="Bidmead_1985_CCPM286"/>

Concurrent DOS 286 was a complete rewrite in the [[C (programming language)|C language]] based on a new system architecture with dynamically loadable device drivers instead of a static BIOS or XIOS.<ref name="BYTE_1985_CDOS286"/> One of its main architects was Francis "Frank" R. Holsworth<!-- born 19??-09-04 https://amaus.net/static/S100/software/DRI/Digital%20Dialogue/03x04%20198408%20Digital%20Dialogue.pdf -->.<ref name="Wein_2002"/><ref name="Holsworth_2006"/> The operating system would function strictly in [[Intel 80286|80286]] native mode, allowing [[protected mode]] [[multi-user]], multitasking operation while running [[8086 emulation mode|8086 emulation]].<ref name="Infoworld_1985_Super"/><ref name="BYTE_1985_CDOS286"/> While this worked on the B-1 [[stepping level|step]] of prototype chip samples, Digital Research, with evaluation copies of their operating system already shipping in April, discovered problems with the emulation on the production level C-1 step of the processor in May, which would not allow Concurrent DOS 286 to run [[Intel 8086|8086]] software in protected mode. The release of Concurrent DOS 286 had been scheduled for late May, but was delayed until Intel could develop a new version of the chip.<ref name="Infoworld_1985_Super"/> In August, after extensive testing E-1 step samples of the 80286, Digital Research said that Intel had corrected all documented 286 [[errata]], but that there were still undocumented chip performance problems with the prerelease version of Concurrent DOS 286 running on the E-1 step. Intel said that the approach Digital Research wished to take in emulating 8086 software in protected mode differed from the original specifications; nevertheless they incorporated into the E-2 step minor changes in the [[microcode]] that allowed Digital Research to run emulation mode much faster (see [[286 LOADALL|LOADALL]]).<ref name="Infoworld_1985_80286"/><ref name="DRI_1986_CDOS68K-2"/> These same limitations affected [[FlexOS 286]] version 1.x, a reengineered derivation of Concurrent DOS 286,<ref name="DRI_1986_FlexOS286"/><ref name="CBR_1987_FlexOS-286"/> which was developed by Digital Research's new Flexible Automation Business Unit in Monterey, California, since 1986.

Later versions added compatibility with PC DOS 2.x and 3.x.

Known versions include:

* Concurrent DOS 286 1.0 (1985)<ref name="DRI_1986_CDOS68K-2"/>
* Concurrent DOS 286 1.1 (1986-01-07)<ref name="DRI_1986_CDOS68K-2"/>
* Concurrent DOS 286 1.2 (1986)<ref name="Meta_1986_HighC12"/>
* [[FlexOS 286 1.3]] (November 1986)<ref name="DRI_1986_FlexOS286"/>
* [[FlexOS 286 1.31]] (May 1987)

==={{anchor|VIOS|CDOS386|CPCDOS5.0|CPCDOS5.2|CDOSXM}}Concurrent DOS XM and Concurrent DOS 386===
{{See also|GEM XM}}
[[File:Digital Research Concurrent DOS XM Release 6.0 720x400.png|thumb|Digital Research Concurrent DOS XM Release 6.0]]
[[File:Digital Research Concurrent DOS 386 Release 2.0 720x400.png|thumb|Digital Research Concurrent DOS 386 Release 2.0]]
The OEM Support Group was relocated into Digital Research's newly created European Development Centre (EDC) in [[Hungerford]], [[United Kingdom|UK]] in 1986, which started to take over further development of the Concurrent DOS family since Concurrent DOS 4.11, including siblings like [[DOS Plus]] and successors.

Developed in Hungerford, UK, versions 5 and 6 (Concurrent DOS XM, with XM standing for [[Expanded Memory]]) could [[bank switching|bank switch]] up to 8&nbsp;MB of [[Enhanced Expanded Memory Specification|EEMS]] to provide a [[real-mode]] environment to run multiple CP/M-86 and DOS programs concurrently and support up to three users (one local and up to two hooked up via serial terminals).

In 1987, Concurrent DOS 86 was rewritten to become Concurrent DOS 386,<ref name="IW_1987_MDOS386"/> still a continuation of the classical XIOS & BDOS architecture.<!-- in contrast to Concurrent DOS 68K, Concurrent DOS 286 and FlexOS --> This ran on machines equipped with the [[Intel 80386]] and later processors, using the 386's hardware facilities for [[Hardware-assisted virtualization|virtualizing]] the hardware, allowing most DOS applications to run unmodified under Concurrent DOS 386, even on terminals. The OS supported concurrent multiuser file access, allowing multiuser applications to run as if they were on individual PCs attached to a network [[Server (computing)|server]]. Concurrent DOS 386 allowed a single server to support a number of users on dumb terminals or inexpensive low-specification PCs running terminal emulation software, without the need for expensive workstations and then-expensive network cards. It was a true multiuser system; several users could use a single database with [[record locking]] to prevent mutual interference.<ref name="the_computer_chronicles_multitasking_concurrent_dos">{{YouTube|id=IKzleg4AcXg|title = Concurrent DOS demonstration in the episode "Multitasking" of the Computer Chronicles |time=4m46s}}</ref><ref>{{Cite magazine |date=November–December 1987 |title=Concurrent DOS 386 |magazine=Micro/Systems Journal |last=Soya |first=Alex K. H. |url=https://archive.org/details/msj-v-3n-6/page/28/mode/2up |access-date=2025-12-23 |pages=28–33 |volume=3 |issue=6 |issn=8750-9482}}</ref>

Concurrent DOS 386 uses about 200K of [[conventional memory]], much more than MS-DOS. ''[[BYTE]]'' said that with the software's minimum requirement of 512K RAM "all you can do is admire the system prompt", and estimated that 1MB RAM in addition to the base 640K allows for using three major applications like [[Microsoft Word]] or [[Multiplan]].<ref name="lane198807">{{Cite magazine |last=Lane |first=Alex |date=July 1988 |title=Concurrent DOS 386 |url=https://archive.org/details/byte-1988-07_202104/page/163/mode/1up?view=theater |access-date=2025-04-12 |magazine=BYTE |pages=163–170}}</ref>

Concurrent DOS 6.0 represented also the starting point for the [[DR DOS]] family, which was carved out of it.

Known 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 5.1?, January 1987)
* DR Concurrent DOS XM 5.2 (BDOS 5.2?, September 1987)<ref name="Angus_1987_52-11"/><ref name="CDOSXM52_2001"/><ref name="Fisher_1987_CompuPro"/>
* DR Concurrent DOS XM 6.0 (BDOS 6.0, 1987-11-18),<!-- reports as PC DOS 3.30, %OS%=CDOS, %VER%=6.0 --><ref name="Ryan_1987"/><ref name="CDOS60"/> 6.01 (1987)
* DR Concurrent DOS XM 6.2 (BDOS 6.2),<!-- %OS%=CDOS, %VER%=6.2 --><ref name="CDOS386_COMDEX"/> 6.21
;
;
* DR Concurrent DOS 386 1.0 (BDOS 5.0?, 1987)
* DR Concurrent DOS 386 1.1 (BDOS 5.2?, September 1987)<ref name="Angus_1987_52-11"/>
* DR Concurrent DOS 386 2.0 (BDOS 6.0, 1987-11-18<!-- reports as PC DOS 3.30, %OS%=CDOS386, %VER%=2.0-->),<ref name="Ryan_1987"/> 2.01<!-- (BDOS 6.?) --><ref name="Schulman_1994_Undocumented-DOS"/>
* DR Concurrent DOS 386 3.0 (BDOS 6.2, December 1988, January 1989<!-- %OS%=CDOS386, %VER%=3.0 -->),<ref name="CDOS386_COMDEX"/> 3.01 (1989-05-19), 3.02 (1989)

Concurrent PC DOS XM 5.0 emulated IBM PC DOS 2.10,<ref name="1986_CDOSXM"/> whereas Concurrent DOS XM 6.0 and Concurrent DOS 386 2.0 were compatible with IBM PC DOS 3.30.<ref name="DRI_1988_CDOS"/>

====Reception====
''BYTE'' in 1988 described Concurrent DOS 386 as "substantially compatible" with MS-DOS; [[Microsoft Word]] 3.1 ran, for example, while 4.0 did not because of its use of undocumented DOS functions. The magazine reported that performance decreased proportionately to the number of simultaneous applications. In contrast to the higher RAM requirement, ''BYTE'' found that video I/O was twice as fast as on DOS. The magazine concluded that while "bigger and better" 386 operating systems were coming, Concurrent DOS 386 "is here today and ready to go".{{r|lane198807}}

===={{anchor|CCI-CDOS}}Adaptations====
Known CCI Concurrent DOS adaptations by Concurrent Controls, Inc. include:

* CCI Concurrent DOS 386 1.12 (BDOS 5.0?, October 1987)
* CCI Concurrent DOS 386 2.01 (BDOS 6.0?, May 1988)
* CCI Concurrent DOS 386 3.01 (BDOS 6.2?, March 1989)
* CCI Concurrent DOS 386 3.02 (April 1990)
* CCI Concurrent DOS 386 3.03 (March 1991)
* CCI Concurrent DOS 386 3.04 (July 1991)<ref name="Scannell_1991_Scripting"/> aka "CCI Concurrent DOS 4.0"<ref name="Scannell_1991_Concurrent"/>
* CCI Concurrent DOS 3.05 R1 (1992-02), R2 (1992), R3+R4 (1992), R5+R6 (1992), R7+R8 (1993), R9+R10 (1993), R11 (August 1993)
* CCI Concurrent DOS 3.06 R1 (December 1993), R2+R3 (1994), R4+R5+R6 (1994), R7 (July 1994)
* CCI Concurrent DOS 3.07 R1 (March 1995), R2 (1995), R3 (1996), R4 (1996), R5 (1997), R6 (1997), R7 (June 1998)<ref name="CCI_1998_CDOS"/>
* CCI Concurrent DOS 3.08
<!-- * CCI Concurrent DOS 3.09 to be enabled when a RS is found that it existed -->
* CCI Concurrent DOS 3.10 R1 (2003-10-05)<ref name="CCI_2003_CDOS310R1"/>

Other adaptations include:

* [[Apricot Computers|Apricot]] Concurrent DOS 386 2.01 (1987) for Apricot Quad Version Level 4.3<ref name="Apricot_CDOS"/>

=={{anchor|MDOS|5.0|5.1}}Multiuser DOS==
<!-- This section may be linked to from inside or outside this article. Do not rename without keeping in sync. -->
{{About|Concurrent DOS|other uses|MDOS (disambiguation)|section=yes}}

Later versions of Concurrent DOS 386 incorporated some of the enhanced functionality of DR's later single-user PC DOS clone [[DR DOS 5.0]], after which the product was given the more explanatory name "Multiuser DOS" (a.k.a. MDOS), starting with version 5.0 (with BDOS 6.5) in 1991.<ref name="Scannell_1991_Tools"/>

Multiuser DOS suffered from several technical limitations that restricted its ability to compete with [[local area network|LANs]] based on [[PC DOS]]. It required its own special [[device driver]]s for much common hardware, as PC DOS drivers were not multiuser or multi-tasking aware. Driver installation was more complex than the simple PC DOS method of copying the files onto the boot disk and modifying [[CONFIG.SYS]] appropriately{{snd}} it was necessary to relink the Multiuser DOS [[Kernel (operating system)|kernel]] (known as a ''nucleus'') using the [[SYSGEN]] command.

Multiuser DOS was also unable to use many common PC DOS additions such as [[network stack]]s, and it was limited in its ability to support later developments in the PC-compatible world, such as [[graphics adaptor]]s, [[sound card]]s, [[CD-ROM]] drives and mice. Although many of these were soon rectified{{snd}} for example, graphical terminals were developed, allowing users to use [[Color Graphics Adapter|CGA]], [[Enhanced Graphics Adapter|EGA]] and [[Video Graphics Array|VGA]] software{{snd}} it was less flexible in this regard than a network of individual PCs, and as the prices of these fell, it became less and less competitive, although it still offered benefits in terms of management and lower total cost of ownership. As a multi-user operating system its price was higher than a single-user system, of course, and it required special device drivers, unlike single-user multitasking DOS add-ons such as [[Quarterdeck Office Systems|Quarterdeck's]] [[DESQview]]. Unlike MP/M, it never became popular for single-user but multitasking use.

When Novell acquired Digital Research in 1991<ref name="Scott_1991"/><ref name="BW_1991"/><ref name="Allchin_1992"/> and abandoned Multiuser DOS in 1992, the three Master VARs DataPac Australasia, Concurrent Controls<ref name="Barney_1994_CCI"/> and Intelligent Micro Software<ref name="Pontin_1995_IMS"/> were allowed to license the source code of the system to take over and continue independent development of their derivations in 1994.

Known versions include:

* DR Multiuser DOS 5.00 (1991),<ref name="CW_1991_DRMDOS50"/> 5.01
* Novell DR Multiuser DOS 5.10 (1992-04-13),<ref name="CW_MDOS51"/> 5.11<ref name="CCI_FPROD"/>
* Novell DR Multiuser DOS 5.13 (BDOS 6.6<!-- 1466 -->, 1992)

All versions of Digital Research and Novell DR Multiuser DOS reported themselves as "IBM PC DOS" version 3.31.

===Adaptations===
===={{anchor|Datapac|System Manager}}DataPac Australasia====
<!-- This section may be linked to from inside or outside this article. Do not rename without keeping in sync. -->

Known versions by DataPac Australasia Pty Limited include:

* Datapac Multiuser DOS 5.0
* Datapac Multiuser DOS 5.1 (BDOS 6.6)
<!-- * Datapac System Manager 5.0? did it exist? -->
* Datapac System Manager 7.0 (1996-08-22)

<!-- System Manager found market acceptance as NetWare dial-in WAN servers and as multiuser servers for cheaper terminals in China. -->
In 1997, Datapac was bought by [[Citrix Systems, Inc.]],<ref name="Citrix_1997"/><ref name="Duursma_2006_Citrix"/><ref name="Costello_1997_DataPac"/> and System Manager was abandoned soon after. In 2002 the Sydney-based unit was spun out into Citrix' Advanced Products Group.<ref name="Mulcaster_2002"/>

===={{anchor|CCI|CCI7.00|CCI7.10|CCI7.21|CCI7.22}}Concurrent Controls====
<!-- This section may be linked to from inside or outside this article. Do not rename without keeping in sync. -->

Known CCI Multiuser DOS versions by Concurrent Controls, Inc. (CCI) include:

* CCI Multiuser DOS 7.00
* CCI Multiuser DOS 7.10
* CCI Multiuser DOS 7.21<ref name="CCI_1997_HELP"/>
* CCI Multiuser DOS 7.22<ref name="CCI_1997_HELP"/> R1 (September 1996), R2 (1996), R3 (1997), R4 GOLD/PLUS/LITE (BDOS 6.6<!-- 1466h -->, 1997-02-10), R5 GOLD (1997), R6 GOLD (1997), R7 GOLD (June 1998), R8 GOLD, R9 GOLD, R10 GOLD, R11 GOLD (2000-09-25), R12 GOLD (2002-05-15), R13 GOLD (2002-07-15), R14 GOLD (2002-09-13), R15 GOLD, R16 GOLD (2003-10-10), R17 GOLD (2004-02-09), R18 GOLD (2005-04-21)<!-- 2004? -->

All versions of CCI Multiuser DOS report themselves as "IBM PC DOS" version 3.31.<ref name="CCI_1997_HELP"/> Similar to [[SETVER]] under [[DOS]], this can be changed using the Multiuser DOS {{mono|DOSVER&nbsp;x.y}} utility.<ref name="CCI_1997_HELP"/>

In 1999, CCI changed its name to Applica, Inc.<ref name="CCI_1999_Applica"/> In 2002 Applica Technology became Aplycon Technologies, Inc.<ref name="Aplycon_2002_Applica"/>

===={{anchor|IMS}}Intelligent Micro Software, Itera and Integrated Solutions====

=====DOS 386 Professional=====
{{Expand section|date=January 2017}}

====={{anchor|IMS5.1|IMS5.11|IMS5.14|IMS7.0|IMS7.1}}IMS Multiuser DOS=====
Known adaptations of IMS Multiuser DOS include:

* IMS Multiuser DOS Enhanced Release 5.1 (1992)
* IMS Multiuser DOS 5.11
* IMS Multiuser DOS 5.14
* IMS Multiuser DOS 7.0
* IMS Multiuser DOS 7.1 (BDOS 6.7<!-- 1467h -->, 1994)

All versions of IMS Multiuser DOS report themselves as "IBM PC DOS" version 3.31.

====={{anchor|7.50|7.51|7.52|7.53|7.54|7.60|7.61|7.62|7.63|7.70|7.71|7.72|7.73|7.74|7.80|7.81|7.82|7.83|7.90|7.91|7.92|7.93|7.94|7.95}}REAL/32=====
<!-- This section may be linked to from inside or outside this article. Do not rename without keeping in sync. -->
[[File:IMS REAL-32 Version 7.6 720x400.png|thumb|IMS REAL/32 Version 7.6]]
Intelligent Micro Software Ltd. (IMS) of [[Thatcham]], UK, acquired a license to further develop Multiuser DOS from Novell in 1994 and renamed their product REAL/32 in 1995.<ref name="Pontin_1995_IMS"/>

Similar to [[FlexOS]]/[[4690 Operating System|4690 OS]] before, IBM in 1995 licensed REAL/32 7.50 to bundle it with their 4695 POS terminals.<ref name="Pontin_1995_IMS"/>{{clarify|date=September 2018|reason=Not clear if this replaces FlexOS 386 on these systems, or if merely upgrades some parts of FlexOS from REAL/32.}}

IMS REAL/32 versions:

* IMS REAL/32 7.50 (BDOS 6.8<!-- 1468h -->, 1995-07-01), 7.51 (BDOS 6.8<!-- 1468h -->), 7.52 (BDOS 6.9<!-- 1469h -->), 7.53 (BDOS 6.9<!-- 1469h -->, 1996-04-01), 7.54 (BDOS 6.9<!-- 1469h -->, 1996-08-01)<ref name="RM_1996_754"/>
* IMS REAL/32 7.60 (BDOS 6.9<!-- 1469h -->, February 1997),<ref name="MaxFrame_2001_760"/> 7.61, 7.62, 7.63
* IMS REAL/32 7.70 (November 1997), 7.71, 7.72, 7.73, 7.74 (1998)<ref name="MaxFrame_2001_774"/>
* IMS REAL/32 7.80, 7.81 (February 1999), 7.82, 7.83 (BDOS 6.10<!-- 146Ah -->)
* IMS REAL/32 7.90 (1999)<!-- before August 1999 -->,<ref name="IMS_1999_R32-790"/> 7.91, 7.92
* ITERA IMS REAL/32 7.93 (June 2002<!-- or November 2002 -->),<ref name="IMS_2002_R32-793"/> 7.94 (BDOS 6.13<!-- 146Dh -->, 2003-01-31)<ref name="IMS_2003_R32-794"/>
* Integrated Solutions IMS REAL/32 7.95<!-- (August 2010 or earlier) --><ref name="IS_2010_R795"/>

REAL/32 7.50 to 7.74 report themselves as "IBM PC DOS" version 3.31, whereas 7.80 and higher report a version of 6.20.<!-- this holds true at least up to 7.94, not sure about 7.95 --> [[Logical Block Addressing|LBA]] and [[FAT32]] support was added with REAL/32 7.90 in 1999.<ref name="IMS_1999_R32-790"/> On 19 April 2002, Intelligent Micro Software Ltd. filed for insolvency and was taken over by one of its major customers, Barry<!-- Stuart --> Quittenton's Itera Ltd.<ref name="LII_2002_Discontinued"/><ref name="LII_2002_NewOwner"/><ref name="LII_2002_ITERA"/> This company was dissolved on 2006-03-28.<ref name="ITERA_UK"/><ref name="NEXOK_Itera"/> As of 2010 REAL/32 was supplied by Integrated Solutions<!-- Ltd. --> of Thatcham, UK, but the company, at the same address, was later listed as builders.<ref name="IS_2010_R795"/>

=====REAL/NG=====
<!-- This section may be linked to from inside or outside this article. Do not rename without keeping in sync. -->
REAL/NG was <!-- ITERA? -->IMS' attempt to create the "Next Generation" of REAL/32, also named "REAL/32 for the internet age". REAL/NG promised "increased range of hardware from PCs to x86 multi-processor server systems".<ref name="realng"/>

Advertised feature list, as of 2003:<ref name="keyfeaturesofrealng"/>

* Runs with [[Red Hat Linux|Red Hat 7.3]] or later version of [[Linux]]
* [[Backward compatible]] with DOS and REAL/32
* Max 65535 [[virtual console]]s; each of these can be a user
* No Linux expertise required
* Administration/setup/upgrade by web browser (local and remote)
* Supplied with [[TCP/IP]] Linux-/Windows-based terminal emulator for the number of users purchased
* Print and file sharing built in
* [[Drive mapping]] between Linux and REAL/NG servers built in
* User hardware support
* Increased performance
* Vastly increased TPA
* [[Multi-processor]] support
* Improved hardware support
* Built-in firewall support
* Very low cost per seat
* Low total cost of ownership
* Supplied on CD
* Supplied with a set of Red Hat CDs

By 10 December 2003, IMS made "REALNG V1.60-V1.19-V1.12" available,<ref name="realng_probablylatest"/> which, based on the [[Internet Archive]], seems to be the latest release.

By 2005, the realng.com website was mirroring the IMS main website, and had no mention of REAL/NG, only REAL/32.<ref name="realng_disappear"/>

==Application software==
While the various releases of this operating system had increasing ability to run DOS programs, software written for the platform could take advantage of its features by using [[function call]]s specifically suitable for multiuser operation. It used [[pre-emptive multitasking]], preventing badly-written applications from delaying other processes by retaining control of the processor. To this day, Multiuser DOS is supported by popular [[Transport Layer Security|SSL/TLS]] libraries such as [[wolfSSL]].

The [[API]] provided support for blocking and non-blocking [[message queue]]s, mutual-exclusion queues, the ability to create sub-process [[Thread (computer science)|threads]] which executed independently from the parent, and a method of pausing execution which did not waste [[processor cycle]]s, unlike idle loops used by single-user operating systems. Applications were started as "attached" to a [[virtual console|console]]. However, if an application did not need user interaction it could "detach" from the console and run as a [[background process]], later reattaching to a console if needed.

Another key feature was that the [[memory management]] supported a "shared" [[Memory model (computing)|memory model]] for processes (in addition to the usual models available to normal DOS programs). In the shared memory model the "code" and "data" sections of a program were isolated from each other. Because the "code" contained no modifiable data, code sections in memory could be shared by several processes running the same program, thereby reducing memory requirements.

Programs written, or adapted, for any [[Computer multitasking|multitasking]] platform need to avoid the technique used by single-tasking systems of going into endless loops until interrupted when, for example, waiting for a user to press a key; this wasted processor time that could be used by other processes. Instead, Concurrent DOS provided an API call which a process could call to "sleep" for a period of time. Later versions of the Concurrent DOS kernel included Idle Detection, which monitored [[DOS API]] calls to determine whether the application was doing useful work or in fact idle, in which case the process was suspended allowing other processes to run. Idle Detection was the catalyst for the patented [[DR-DOS]] [[Dynamic Idle Detection]] power management feature invented in 1989 by Roger Alan Gross and John P. Constant and marketed as [[BatteryMAX]].<ref name="US5355501"/>

==See also==
* [[CP/M]]
* [[MP/M]]
* [[Concurrent DOS V60]]
* [[FlexOS]]
* [[DR&nbsp;DOS]]
* [[PC DOS]] – IBM's OEM version of (single-user) MS-DOS
* [[MS-DOS 4.0 (multitasking)]]
* [[PC-MOS/386]] – unrelated multitasking DOS clone
* [[VM/386]] – unrelated multitasking DOS environment
* [[Virtual DOS machine]]
* [[Multiuser DOS Federation]]
* [[Timeline of operating systems]]
* [[List of mergers and acquisitions by Citrix]]

==References==
<references>

<ref name="RM_1996_754">{{cite web |author-first=R. |author-last=M. |title=REAL/32 Upgrade Disk – Version 7.54 – Batch 08-96-01 – SRN0167.WP |id=R32UP754.ZIP |date=1996-07-31 |url=http://contents.driverguide.com/content.php?id=582964&path=SRN0167.TXT |access-date=2017-01-17 |url-status=live |archive-url=https://web.archive.org/web/20180826200229/https://contents.driverguide.com/content.php?id=582964&path=SRN0167.TXT |archive-date=2018-08-26}}</ref>
<ref name="DRI_1984_CCPM31">Digital Research (1984): ''Concurrent CP/M ships early in response to team effort''. [[Digital Dialogue (Digital Research)|Digital Dialogue]] – Employee Newsletter of Digital Research Inc., Volume 3, Number 1, p.&nbsp;1 ([http://corphist.computerhistory.org/corphist/view.php?s=documents&id=1008]).</ref>
<ref name="CCPM_1984">{{cite web |title=Concurrent CP/M with Windows Operating System – Technical Note for the IBM Personal Computer and Personal Computer XT |edition=1 |date=February 1984 |publisher=[[Digital Research]] |url=http://bitsavers.informatik.uni-stuttgart.de/pdf/digitalResearch/concurrent/4007-1010_Concurrent_CPM_with_Windows_Technical_Note_for_IBM_PC_Feb84.pdf |access-date=2017-01-04 |url-status=live |archive-url=https://web.archive.org/web/20170104170035/http://bitsavers.informatik.uni-stuttgart.de/pdf/digitalResearch/concurrent/4007-1010_Concurrent_CPM_with_Windows_Technical_Note_for_IBM_PC_Feb84.pdf |archive-date=2017-01-04}}</ref>
<ref name="Kildall_1982_8-bit">{{cite journal |title=Running 8-bit software on dual-processor computers |author-first=Gary Arlen |author-last=Kildall |author-link=Gary Arlen Kildall |journal=[[Electronic Design]] |date=1982-09-16 |page=157 |url=http://archive.computerhistory.org/resources/access/text/2016/12/102762506-05-01-acc.pdf |access-date=2017-08-19 |url-status=live |archive-url=https://web.archive.org/web/20170819183737/http://archive.computerhistory.org/resources/access/text/2016/12/102762506-05-01-acc.pdf |archive-date=2017-08-19}}</ref>
<ref name="DRI_1984_PCMODE">Digital Research (1984): ''PC-Mode bridges CP/M and PC-DOS''. [[Digital Dialogue (Digital Research)|Digital Dialogue]] – Employee Newsletter of Digital Research Inc., Volume 3, Number 1, p.&nbsp;3 ([http://corphist.computerhistory.org/corphist/view.php?s=documents&id=1008]).</ref>
<ref name="DRI_1984_CCPM31b">Digital Research: ''Concurrent CP/M Release 3.1 offers PC-DOS compatibility''. [[Digital Research News]] – For Digital Research Users Everywhere, Volume 4, No. 1, p.&nbsp;5, first quarter 1984 ([http://corphist.computerhistory.org/corphist/view.php?s=documents&id=1013]): "Concurrent CP/M Release 3.1 replaces MP/M-86 as Digital Research's multiuser system. Targeted at 16-bit microcomputers, Release 3.1 may also be configured for a single user environment. Kevin Wandryk, product line manager for the new release, said the PC-DOS mode in the new release increases the availability of applications software. End users can choose between products for Concurrent CP/M or PC-DOS. Digital Research will provide a list of those applications from PC-DOS which may be used, Wandryk said. The manufacturer's version was introduced in December at the COMDEX/Fall trade show in Las Vegas and is scheduled to ship in March."</ref>
<ref name="CCI_1997_HELP">{{cite book |title=CCI Multiuser DOS 7.22 GOLD Online Documentation |id=HELP.HLP |date=1997-02-10 |publisher=[[Concurrent Controls, Inc.]] (CCI)}}</ref>
<ref name="Scott_1991">{{cite news |title=Novell/DRI merger to reap better client management |author-first=Karyl |author-last=Scott |date=1991-07-29 |series=Networking |newspaper=[[InfoWorld]] |issn=0199-6649 |volume=13 |issue=30 |page=33 |publisher=[[InfoWorld Publishing Co.]] |url=https://books.google.com/books?id=mVAEAAAAMBAJ&pg=PA33 |access-date=2017-01-21 |url-status=live |archive-url=https://web.archive.org/web/20200209155946/https://books.google.de/books?id=mVAEAAAAMBAJ&pg=PA33&lpg=PA33&redir_esc=y |archive-date=2020-02-09}}</ref>
<ref name="BW_1991">{{cite news |title=Novell and Digital Research sign definitive merger agreement |date=1991-07-17 |work=[[Business Wire]] |url=http://tech-insider.org/personal-computers/research/1991/0717.html |access-date=2017-01-24 |url-status=live |archive-url=https://web.archive.org/web/20180818133749/https://tech-insider.org/personal-computers/research/1991/0717.html |archive-date=2018-08-18}}</ref>
<ref name="Allchin_1992">{{cite web |title=Novell/Digital Research reach definitive agreement… |author-first=Jim |author-last=Allchin |author-link=Jim Allchin |date=1992-05-27 |orig-year=1991-07-17 |type=Court document |id=Plaintiff's exhibit 828, [[Comes v. Microsoft]] |url=http://antitrust.slated.org/www.iowaconsumercase.org/011607/0000/PX00838.pdf |access-date=2017-01-21 |url-status=live |archive-url=https://web.archive.org/web/20161119074834/http://antitrust.slated.org/www.iowaconsumercase.org/011607/0000/PX00838.pdf |archive-date=2016-11-19}}</ref>
<ref name="Barney_1994_CCI">{{cite journal |title=CCI helps users run more DOS apps – Multiuser DOS Lite handles eight NetWare sessions |author-first=Doug |author-last=Barney |journal=[[InfoWorld]] |date=1994-07-25 |page=20 |url=https://books.google.com/books?id=kDgEAAAAMBAJ&pg=PA20 |access-date=2018-08-19}}</ref>
<ref name="Pontin_1995_IMS">{{cite journal |title=IMS offers Real32 OS for application servers |author-first=Jason |author-last=Pontin |date=1995-11-27 |journal=[[InfoWorld]] |url=https://books.google.com/books?id=VzgEAAAAMBAJ&pg=PA28 |access-date=2017-01-17}}</ref>
<ref name="CW_1991_DRMDOS50">{{cite journal |title=Digital Research präsentiert Multiuser-DOS |language=de |date=1991-03-22 |author=CW |journal=[[Computerwoche]] |url=https://www.computerwoche.de/a/digital-research-praesentiert-multiuser-dos,1139066 |access-date=2018-08-19 |url-status=live |archive-url=https://web.archive.org/web/20180819150822/https://www.computerwoche.de/a/digital-research-praesentiert-multiuser-dos,1139066 |archive-date=2018-08-19}}</ref>
<ref name="US5355501">{{cite patent |number=5355501 |country=US|status=patent|title=Idle Detection System |inventor1-first=Roger Alan |inventor1-last=Gross |inventor2-first=John P. |inventor2-last=Constant |gdate=1994-10-11 |fdate=1990-03-09 |url=https://patents.google.com/patent/US5355501A/en}}</ref>
<ref name="DRI_1984_CDOS31">Digital Research: ''Concurrent DOS bridges PC-DOS, CP/M''. [[Digital Research News]] – For Digital Research Users Everywhere, Volume 4, No. 2, p.&nbsp;3, May 1984 ([http://corphist.computerhistory.org/corphist/view.php?s=documents&id=1011]): '"Concurrent DOS Release 3.1 is rapidly gaining momentum and support from a wide range of microcomputer manufacturers," Wandryk said. "Some 60 hardware companies have licensed the product since it was released in early March."'</ref>
<ref name="Knox_1986_CDOS68K">{{cite newsgroup |title=Re: DRI Concurrent DOS for 68K |author-first=James M. |author-last=Knox |newsgroup=mod.computers.68k |date=1986-06-22 |url=http://www.megalextoria.com/usenet-archive/news044f1/b64/mod/computers/68k/00000078.html |access-date=2018-09-13 |url-status=live |archive-url=https://archive.today/20180913210113/http://www.megalextoria.com/usenet-archive/news044f1/b64/mod/computers/68k/00000078.html |archive-date=2018-09-13}}</ref>
<ref name="Knox_1987_DRI">{{cite newsgroup |title=CDOS-68K |author-first=James M. |author-last=Knox |newsgroup=mod.computers.68k |date=1987-01-31 |url=https://macgui.com/usenet/?group=78&start=80&id=27 |access-date=2018-09-13 |url-status=live |archive-url=https://archive.today/20180913210221/https://macgui.com/usenet/?group=78&start=80&id=27 |archive-date=2018-09-13}}</ref>
<ref name="DRI_1986_CDOS68K-1">{{cite web |title=Concurrent DOS 68K 1.2 – Developer Kit for Motorola VME/10 – Disk 1 |date=1986-08-06 |orig-year=1986-04-08 |url=http://www.cpm.z80.de/download/cdos1.zip |access-date=2018-09-13 }}</ref>
<ref name="DRI_1986_CDOS68K-2">{{cite web |title=Concurrent DOS 68K 1.2 – Developer Kit for Motorola VME/10 – Disk 2 |date=1986-08-06 |orig-year=1986-04-08 |url=http://www.cpm.z80.de/download/cdos2.zip |access-date=2018-09-13 }} (NB. This package also includes some header files from [[Concurrent DOS 286]], including STRUCT.H explicitly mentioning [[LOADALL]] for "8086 emulation".)</ref>
<ref name="DRI_1986_CDOS68K-3">{{cite web |title=Concurrent DOS 68K 1.2 – Developer Kit for Motorola VME/10 – Disk 3 |date=1986-08-06 |orig-year=1986-04-08 |url=http://www.cpm.z80.de/download/cdos3.zip |access-date=2018-09-13 }}</ref>
<ref name="Infoworld_1985_Super">{{cite journal |author-first=Edward |author-last=Foster |title=Super DOS awaits new 80286 – Concurrent DOS 286 – delayed until Intel upgrades chip – offers Xenix's power and IBM PC compatibility |publisher=[[InfoWorld Media Group]] |journal=[[InfoWorld]] |volume=7 |issue=19 |date=1985-05-13 |issn=0199-6649 |pages=17–18 |url=https://books.google.com/books?id=2y4EAAAAMBAJ&pg=PA17}}</ref>
<ref name="BYTE_1985_CDOS286">{{cite journal |title=Concurrent DOS-286 Challenges Unix |journal=[[BYTE Magazine]] |date=May 1985 |volume=10 |number=5 |page=375-377<!-- plus more --> |url=http://tech-insider.org/personal-computers/research/1985/05.html |access-date=2017-01-23 |url-status=live |archive-url=https://archive.today/20180914120059/https://tech-insider.org/personal-computers/research/1985/05.html |archive-date=2018-09-14}} [https://archive.org/stream/byte-magazine-1985-05/1985_05_BYTE_10-05_Multiprocessing#page/n376/mode/1up/search/concurrent]</ref>
<ref name="Meta_1986_HighC12">{{cite book |title=High C Programmer's Guide – Version 1.2 for Concurrent DOS |publisher=[[MetaWare Incorporated]] |location=Santa Cruz, CA, USA |date=1986 |orig-year=1985-09-15 |edition=1 |url=http://www.bitsavers.org/pdf/metaware/High_C_Programmers_Guide_1.2_Concurrent_DOS_Sep85.pdf |access-date=2018-08-14 |quote=[…] This is a guide to the operation of the High C compiler as implemented for the Concurrent DOS 286 1.2 or later operating system – hereafter abbreviated to just "Concurrent" per Digital Research custom – running on the Intel 80286 microprocessor and using the Intel Object-Module Format (OMF). The compiler generates code for any of the Intel 8086/88/186/188/286 family of microprocessors. […]}}</ref>
<ref name="DRI_1986_FlexOS286">{{cite book |title=FlexOS Supplement for Intel iAPX 286-based Computers |publisher=[[Digital Research, Inc.]] |date=November 1986 |edition=1 |version=1.3 |url=http://www.bitsavers.org/pdf/digitalResearch/flexos/FlexOS_Suppliment_For_iAPX286_Computers_Nov86.pdf |access-date=2018-08-14 |archive-date=2019-04-21 |archive-url=https://web.archive.org/web/20190421183934/http://www.bitsavers.org/pdf/digitalResearch/flexos/FlexOS_Suppliment_For_iAPX286_Computers_Nov86.pdf |url-status=dead }}</ref>
<ref name="MaxFrame_2001_760">{{cite web |title=REAL/32 7.60 for MaxFrame |date=2001-08-20 |publisher=MaxFrame |url=http://www.maxframe.com/DR/REAL32/REAL32-760.ZIP |access-date=2018-09-14 }}</ref>
<ref name="MaxFrame_2001_774">{{cite web |title=REAL/32 7.74 for MaxFrame |date=2001-01-30 |publisher=MaxFrame |url=http://www.maxframe.com/DR/REAL32/MF774R32.zip |access-date=2018-09-14 }}</ref>
<ref name="Gallant_1984">{{cite journal |title=Digital Research, Monterey ink Unix-centered pact |author-first=John |author-last=Gallant |journal=[[Computerworld]] |date=1984-01-23 |volume=XVIII |number=3 |page=6 |url=https://books.google.com/books?id=dRR9VQBwdSIC&pg=PA6 |access-date=2019-02-03}}</ref>
<ref name="Wein_2002">{{cite web |title=Gary Kildall in England |author-first=Josef "Joe" |author-last=Wein |date=2002 |url=https://joewein.de/gary.html |access-date=2019-04-03 |url-status=live |archive-url=https://web.archive.org/web/20190403010811/https://joewein.de/gary.html |archive-date=2019-04-03}}</ref>
<ref name="Holsworth_2006">{{cite web |title=Video: Frank Holsworth, developer |author-first=Francis "Frank" R. |author-last=Holsworth |date=2006-02-01 |id={{CHMID|102770341}}. ITCHP 44403c1a3fd53. Lot Number X7847.2017 |type=interview |publisher=[[Computer History Museum]] |series=Information Technology Corporate Histories Collection |url=https://archive.computerhistory.org/resources/access/moving_image/2017/02/102770341-02-01-acc.wmv |access-date=2019-04-04 |url-status=live |archive-url=https://web.archive.org/web/20190403232808/https://archive.computerhistory.org/resources/access/moving_image/2017/02/102770341-02-01-acc.wmv |archive-date=2019-04-03}}</ref> 
<ref name="Swaine_1982_MPM286">{{cite journal |title=Homebrew Computer Club views Intel's superchip |author-first=Michael |author-last=Swaine |author-link=Michael Swaine (technical author) |date=1982-04-05 |journal=[[InfoWorld]] |volume=4 |number=13 |location=Palo Alto, CA, USA |page=4 |url=https://books.google.com/books?id=ZjAEAAAAMBAJ&pg=PA4 |access-date=2020-01-07 |url-status=live |archive-url=https://web.archive.org/web/20200107223947/https://books.google.com/books?id=ZjAEAAAAMBAJ&pg=PA4&lpg=PA4 |archive-date=2020-01-07 |quote=[…] [[Digital Research]] is producing an operating system for the [[Intel 80286|286]]. [[MP/M-286]] will take advantage of the processor's memory management and protection and virtual memory support. Digital Research is promising "complete" compatibility with its [[MP/M-86]] and [[CP/M-86]] for the [[Intel 8086|8086]] processor. [[Intel]] is supplying Digital Research with the hardware to develop and test MP/M-286. […]}}</ref>
<ref name="Bidmead_1985_CCPM286">{{cite journal |title=Surviving Big Blue |author-first=Christopher H. |author-last=Bidmead |author-link=Christopher H. Bidmead |date=2006-05-09 |orig-year=1985-03-25 |series=Which Computer? |journal=[[Doctor Who (magazine)|Doctor Who]] |url=http://bidmeadia.blogspot.com/2006/05/surviving-big-blue.html |access-date=2020-01-07 |url-status=live |archive-url=https://web.archive.org/web/20200107223658/http://bidmeadia.blogspot.com/2006/05/surviving-big-blue.html |archive-date=2020-01-07 |quote=[…] Paul Bailey of [[Digital Research]] keenly promotes this approach; it is his company that is supplying [[International Computers Limited|ICL]] and others with Concurrent Dos-286. This chameleon operating system allows ICL and other [[Intel 80286|80286]] manufacturers to build machines that will be able to cope with all the existing body of IBM-PC software – and at the same time promise multi-tasking, windowing and true concurrency, three features that together allow a single micro to do several things at once. […] Although no firm announcements have been made, it seems certain that by the end of the year [[Applied Computer Techniques|ACT]] will be offering a [[Concurrent CP/M-286|Concurrent CP/M 286]] machine to fuel its drive into the corporate market. But by this time it will have to contend with [[IBM]]'s own 80286 office micro, the PC/AT. […] IBM also have a software product in the offing that could pull the rug out from under the Concurrent contenders. Some 180K in size, [[TopView]] is a program for IBM PC's and AT's that beefs up the operating system to provide windowing facilities for existing 'well behaved' standard packages. […]}}</ref>
<ref name="DRI_1984_MicroNotes1">{{cite news |title=1 |newspaper=[[Micro Notes (Digital Research)|Micro Notes]] – A Technical Information Quarterly |volume=2 |number=1 |date=First Quarter 1984 |publisher=[[Digital Research, Inc.]] |location=Pacific Grove, CA, USA |url=https://www.z80cpu.eu/mirrors/oldcomputers.dyndns.org/public/pub/manuals/DRI_Micronotes_Vol2_1,2,3_full.pdf |access-date=2020-02-11 |url-status=live |archive-url=https://web.archive.org/web/20200211005618/https://www.z80cpu.eu/mirrors/oldcomputers.dyndns.org/public/pub/manuals/DRI_Micronotes_Vol2_1,2,3_full.pdf |archive-date=2020-02-11}}</ref>
<ref name="DRI_1984_MicroNotes2">{{cite news |title=2 |newspaper=[[Micro Notes (Digital Research)|Micro Notes]] – Technical information on Digital Research products |volume=2 |number=2 |date=May 1984 |publisher=[[Digital Research, Inc.]] |location=Pacific Grove, CA, USA |id=NWS-106-002 |url=https://www.z80cpu.eu/mirrors/oldcomputers.dyndns.org/public/pub/manuals/DRI_Micronotes_Vol2_1,2,3_full.pdf |access-date=2020-02-11 |url-status=live |archive-url=https://web.archive.org/web/20200211005618/https://www.z80cpu.eu/mirrors/oldcomputers.dyndns.org/public/pub/manuals/DRI_Micronotes_Vol2_1,2,3_full.pdf |archive-date=2020-02-11}}</ref>
<ref name="DRI_1984_MicroNotes3">{{cite news |title=3 |newspaper=[[Micro Notes (Digital Research)|Micro Notes]] – Technical information on Digital Research products |volume=2 |number=3 |date=July 1984 |publisher=[[Digital Research, Inc.]] |location=Pacific Grove, CA, USA |id=NWS-106-003 |url=https://www.z80cpu.eu/mirrors/oldcomputers.dyndns.org/public/pub/manuals/DRI_Micronotes_Vol2_1,2,3_full.pdf |access-date=2020-02-11 |url-status=live |archive-url=https://web.archive.org/web/20200211005618/https://www.z80cpu.eu/mirrors/oldcomputers.dyndns.org/public/pub/manuals/DRI_Micronotes_Vol2_1,2,3_full.pdf |archive-date=2020-02-11}}</ref>
<ref name="Schulman_1994_Undocumented-DOS">{{cite book |author-first1=Andrew |author-last1=Schulman |author-first2=Ralf D. |author-last2=Brown |author-link2=Ralf D. Brown |author-first3=David |author-last3=Maxey |author-first4=Raymond J. |author-last4=Michels |author-first5=Jim |author-last5=Kyle |title=Undocumented DOS: A programmer's guide to reserved MS-DOS functions and data structures – expanded to include MS-DOS 6, Novell DOS and Windows 3.1 |publisher=[[Addison Wesley]] |edition=2 |date=1994 |orig-year=November 1993<!-- first printing --> |isbn=0-201-63287-X |location=Reading, Massachusetts, USA |page=203 |url=https://archive.org/details/undocumenteddosp00andr_0 |url-access=registration}} (xviii+856+vi pages, 3.5"-floppy) Errata: [https://web.archive.org/web/20190417215556/http://www.cs.cmu.edu/afs/cs/user/ralf/pub/books/UndocumentedDOS/errata.ud2][https://web.archive.org/web/20190417212906/https://www.pcjs.org/pubs/pc/programming/Undocumented_DOS/#errata-2nd-edition]</ref>
<ref name="LSI_Octopus">[http://oldcomputer.info/8bit/hilger/index.htm LSI Octopus (Hilger Analytical) – MCbx]</ref>
<ref name="CW_1985_CDOS41">{{cite journal |author=CW |title=Concurrent DOS 4.1 in den USA angekündigt |language=de |date=1985-06-21 |journal=[[Computerwoche]] |url=http://www.computerwoche.de/a/concurrent-dos-4-1-in-den-usa-angekuendigt,1169757 |access-date=2017-01-18 |url-status=live |archive-url=https://web.archive.org/web/20170118112800/http://www.computerwoche.de/a/concurrent-dos-4-1-in-den-usa-angekuendigt,1169757 |archive-date=2017-01-18}}</ref>
<ref name="Infoworld_1985_80286">{{cite journal |author-first=Edward |author-last=Foster |title=Intel shows new 80286 chip – Future of DRI's Concurrent DOS 286 still unclear after processor fixed |publisher=[[InfoWorld Media Group]] |journal=[[InfoWorld]] |volume=7 |issue=34 |date=1985-08-26 |issn=0199-6649 |page=21 |url=https://books.google.com/books?id=_y4EAAAAMBAJ&pg=PA21}}</ref>
<ref name="CBR_1987_FlexOS-286">{{cite journal |title=Digital Research launches FlexOS 286 Real-Time Manufacturing Operating System |editor=CBR |journal=Computer Business Review |date=1987-01-15 |url=http://www.cbronline.com/news/digital_research_launches_flexos_286_real_time_manufacturing_operating_system |access-date=2018-09-15 |url-status=live |archive-url=https://archive.today/20130118190950/http://www.cbronline.com/news/digital_research_launches_flexos_286_real_time_manufacturing_operating_system |archive-date=2013-01-18}}</ref>
<ref name="IW_1987_MDOS386">{{cite journal |title=DRI To Release Multiuser 80386 Operating System |author-first=Jiri |author-last=Weiss |journal=[[InfoWorld]] |volume=9 |issue=7 |date=1987-02-16 |pages=1, 8 |url=https://books.google.com/books?id=0DAEAAAAMBAJ&pg=PA1 |access-date=2017-01-22}}</ref>
<ref name="CDOSXM52_2001">{{cite web |title=Question about Concurrent DOS XM 5.2 and CP/M |date=2001-12-08 |work=comp.os.misc |url=https://groups.google.com/d/msg/comp.os.misc/7fej2r5Q7qs/TPhZO5Txm1AJ}}</ref>
<ref name="Fisher_1987_CompuPro">{{cite journal |title=Compupro's 80286-Based Multiuser Machine Features Parallel Processing |author-first=Sharon |author-last=Fisher |date=1987-10-19 |journal=[[InfoWorld]] |page=19 |url=https://books.google.com/books?id=Bz8EAAAAMBAJ&pg=PA19}}</ref>
<ref name="CDOS60">{{cite web |url=http://www.retro-computing.org/?page=item&id=298#mainphoto |title = South-West Retro Computing Archive}}</ref>
<ref name="Angus_1987_52-11">{{cite journal |title=DRI Updates 2 Concurrent DOS Systems |author-first=Jeff |author-last=Angus |date=1987-09-21 |journal=[[InfoWorld]] |url=https://archive.org/details/Infoworld-1987-09-21}}</ref>
<ref name="Ryan_1987">{{cite journal |title=Concurrent DOS 386 fired up |author-first=Alan J. |author-last=Ryan |journal=[[Computerworld]] |volume=21 |issue=42 |date=1987-10-19 |pages=37, 40 |url=https://books.google.com/books?id=IIpG6vryR8AC&pg=PP37 |access-date=2017-01-22 |url-status=live |archive-url=https://web.archive.org/web/20170122151900/https://books.google.com/books?id=IIpG6vryR8AC&pg=PP37&lpg=PP37 |archive-date=2017-01-22}}</ref>
<ref name="CDOS386_COMDEX">{{cite journal |title=Digital to announce Concurrent DOS 386, Release 3.0 at COMDEX |date=1988-11-14 |journal=[[InfoWorld]] |volume=10 |issue=46 |page=29 |url=https://books.google.com/books?id=wTsEAAAAMBAJ&pg=PT28 |access-date=2017-01-22 |url-status=live |archive-url=https://web.archive.org/web/20170122163109/https://books.google.com/books?id=wTsEAAAAMBAJ&pg=PT28&lpg=PT28 |archive-date=2017-01-22}}</ref>
<ref name="1986_CDOSXM">{{cite journal |title=DRI's Latestd Concurrent PC-DOS Touts More Memory |author-first=Mark J. |author-last=Welch |date=1986-06-09 |journal=[[InfoWorld]] |page=20 |url=https://books.google.com/books?id=Ty8EAAAAMBAJ&pg=PA20 |access-date=2018-10-16}}</ref>
<ref name="DRI_1988_CDOS">{{cite web |title=Concurrent DOS – Powerful Multiuser Multitasking Operating Systems |date=1988 |publisher=[[Digital Research]] |url=http://bitsavers.org/pdf/digitalResearch/concurrent/1090-1411-002_Concurrent_DOS_Brochure_1988.pdf |access-date=2018-10-16 }}</ref>
<ref name="Scannell_1991_Scripting">{{cite journal |title=386 Multiuser/Multitasking DOS Gets Scripting Language, File Flush |author-first=Ed |author-last=Scannell |journal=[[InfoWorld]] |date=1991-06-03 |url=https://books.google.com/books?id=SlAEAAAAMBAJ&pg=PA16 |access-date=2017-01-19}}</ref>
<ref name="Scannell_1991_Concurrent">{{cite journal |title=Concurrent revs multiuser DOS |author-first=Ed |author-last=Scannell |journal=[[InfoWorld]] |date=1991-10-07 |page=17 |url=https://books.google.com/books?id=zT0EAAAAMBAJ&pg=PA17 |access-date=2017-01-19}}</ref>
<ref name="CCI_1998_CDOS">{{cite web |title=CCI Concurrent DOS Features |date=1998 |publisher=[[Concurrent Controls, Inc.]] |url=http://www.conctrls.com/CDOSprod.html |url-status=dead |archive-url=https://web.archive.org/web/20050217012319/http://www.conctrls.com/CDOSprod.html |archive-date=2005-02-17}}</ref>
<ref name="CCI_2003_CDOS310R1">{{cite web |title=CCI CDOS V3.10 Release 1 |date=2003 |publisher=[[Concurrent Controls, Inc.]] |url=http://www.conctrls.com/cdosrels.html |url-status=dead |archive-url=https://web.archive.org/web/20050313085453/http://www.conctrls.com/cdosrels.html |archive-date=2005-03-13}}</ref>
<ref name="Apricot_CDOS">{{cite web |url=http://www.retro-computing.org/?page=item&id=304#mainphoto |title = South-West Retro Computing Archive}}</ref>
<ref name="Scannell_1991_Tools">{{cite journal |title=DRI Adds Multiuser Tools To DRDOS; MS DOS 5.0 Release Slips To June |author-first1=Ed |author-last1=Scannell |author-first2=Stuart J. |author-last2=Johnston |date=1991-03-04 |journal=[[InfoWorld]] |volume=13 |issue=9 |pages=1, 97 |url=https://books.google.com/books?id=rlAEAAAAMBAJ&pg=PA97 |access-date=2017-01-21}}</ref>
<ref name="CW_MDOS51">{{Cite web|url=http://www.computerwoche.de/a/digital-research-kommt-mit-der-version-5-1-von-multiuser-dos,1133624|title = Jetz Zugriff auf Novell-Netze möglich: Digital Research kommt mit der Version 5.1 von Multiuser-DOS}}</ref>
<ref name="CCI_FPROD">{{cite web |url=http://conctrls.com/frames/f-prod.htm |title=CONCURRENT CONTROLS: The Multi User Company |website=conctrls.com |access-date=15 January 2022 |archive-url=https://web.archive.org/web/20010619110215/http://conctrls.com/frames/f-prod.htm |archive-date=19 June 2001 |url-status=dead}}</ref>
<ref name="Citrix_1997">{{cite news |title=Citrix to Acquire DataPac Australasia; Acquisition to Accelerate Citrix Presence in High-Growth Asia-Pacific Market |work=[[Business Wire]] |date=1997-09-09 |author=[[Citrix Systems, Inc.]] |location=[[Fort Lauderdale]], FL, USA |url=https://www.thefreelibrary.com/Citrix+to+Acquire+DataPac+Australasia%3B+Acquisition+to+Accelerate...-a019749228 |access-date=2017-01-20}}</ref>
<ref name="Duursma_2006_Citrix">{{cite web |title=Datapac history (Citrix R&D Australia) |date=2006-10-15 |orig-year=2005 |author-first1=Martin |author-last=Duursma |editor-first=Jeff |editor-last=Muir |work=Citrix Blogger |url=https://citrixblogger.org/2006/10/15/datapac-history-citrix-rd-australia/ |access-date=2017-01-19 |url-status=live |archive-url=https://web.archive.org/web/20170120205353/https://citrixblogger.org/2006/10/15/datapac-history-citrix-rd-australia/ |archive-date=2017-01-20}}</ref>
<ref name="Costello_1997_DataPac">{{cite news |title=DataPac sale expected to benefit channel |author-first=John |author-last=Costello |url=http://www.arnnet.com.au/article/114266/datapac_sale_expected_benefit_channel/ |work=Australian Reseller News |date=1997-09-17 |access-date=2015-07-28 |url-status=live |archive-url=https://web.archive.org/web/20170120220419/http://www.arnnet.com.au/article/114266/datapac_sale_expected_benefit_channel/ |archive-date=2017-01-20}}</ref>
<ref name="Mulcaster_2002">{{cite news |title=Citrix leading a silicon charge |author-first=Glenn |author-last=Mulcaster |url=http://www.theage.com.au/articles/2002/10/26/1035504890627.html |work=Australian Reseller News |date=2002-10-29 |access-date=2015-07-28 |url-status=live |archive-url=https://web.archive.org/web/20170120221635/http://www.theage.com.au/articles/2002/10/26/1035504890627.html |archive-date=2017-01-20}}</ref>
<ref name="CCI_1999_Applica">{{cite web |title=Reflecting its continuing focus on the Applica PC-sharing software products, Concurrent Controls Inc. today announced a move to Applica Inc. |author=Applica Inc. |date=1999-11-08 |work=[[PRNewswire]] |location=South San Francisco, CA, USA |url=http://www.prnewswire.com/news-releases/concurrent-controls-announces-change-to-applica-inc-77081802.html |access-date=2017-01-20 |url-status=live |archive-url=https://web.archive.org/web/20160516152918/http://www.prnewswire.com/news-releases/concurrent-controls-announces-change-to-applica-inc-77081802.html |archive-date=2016-05-16}}</ref>
<ref name="Aplycon_2002_Applica">{{cite web |title=Letter to Applica Distributors, Dealers, Partners and Users |author=Aplycon Technologies |date=2002-10-15 |url=http://www.applica.com/ |url-status=live |archive-url=https://web.archive.org/web/20021122081718/http://www.applica.com/ |archive-date=2002-11-22}}</ref>
<ref name="IMS_2002_R32-793">{{cite web |title=Real/32 7.93 Enhancements and Bug fixes |date=2002-11-22 |publisher=[[Intelligent Micro Software]] |url=http://www.imsltd.com/whats_new/new_793.htm |access-date=2017-01-17 |url-status=live |archive-url=https://web.archive.org/web/20170118004218/http://www.imsltd.com/whats_new/new_793.htm |archive-date=2017-01-18}}</ref>
<ref name="IMS_2003_R32-794">{{cite web |title=Real/32 7.94 Enhancements and Bug fixes |date=2003-01-31 |publisher=[[Intelligent Micro Software]] |url=http://www.imsltd.com/whats_new/new_794.htm |access-date=2017-01-17 |url-status=live |archive-url=https://web.archive.org/web/20170118011734/http://www.imsltd.com/whats_new/new_794.htm |archive-date=2017-01-18}}</ref>
<ref name="IS_2010_R795">{{cite web |title=IMS PRICE LIST – AUTUMN 2010 |date=August 2010 |publisher=Integrated Solutions |url=http://www.imsltd.com/pricespecs/price_list.htm |access-date=2017-01-17|archive-url=https://web.archive.org/web/20170118003730/http://www.imsltd.com/pricespecs/price_list.htm |archive-date=2017-01-18}} (NB. Lists REAL/32 7.95.)</ref>
<ref name="IMS_1999_R32-790">{{cite web |title=IMS REAL/32 7.9 Announcement |url=http://www.imsltd.com/products/latest_real32.htm |date=1999 |publisher=[[Intelligent Micro Software]] |url-status=live |archive-url=https://web.archive.org/web/20170118201737/http://www.imsltd.com/products/latest_real32.htm |archive-date=2017-01-18}}</ref>
<ref name="LII_2002_Discontinued">{{cite web |title=REAL/32 products discontinued |date=2002-04-22 |url=http://www.lii.com/NEWS/REAL32Liquidated.htm |publisher=Logan Industries, Inc. (LLI) |url-status=dead |archive-url=https://web.archive.org/web/20030423144710/http://www.lii.com/NEWS/REAL32Liquidated.htm |archive-date=2003-04-23}}</ref>
<ref name="LII_2002_NewOwner">{{cite web |title=REAL/32 under new ownership |date=2002-05-22 |orig-year=2002-05-02 |url=http://www.lii.com/NEWS/REAL32Transition.htm |publisher=Logan Industries, Inc. (LLI) |url-status=dead |archive-url=https://web.archive.org/web/20021203022321/http://www.lii.com/NEWS/REAL32Transition.htm |archive-date=2002-12-03}}</ref>
<ref name="LII_2002_ITERA">{{cite web |title=IMS acquired by ITERA |date=2002-05-23 |url=http://www.lii.com/NEWS/IMSReorganized.htm |publisher=Logan Industries, Inc. (LLI) |url-status=dead |archive-url=https://web.archive.org/web/20030423142937/http://www.lii.com/NEWS/IMSReorganized.htm |archive-date=2003-04-23}}</ref>
<ref name="ITERA_UK">{{citation |title=ITERA LIMITED |publisher=UK Companies List<!-- |url=https://www.companieslist.co.uk/04143290-itera-limited |access-date=2017-01-18 |url-status=live |archive-url=https://web.archive.org/web/20170118214015/https://www.companieslist.co.uk/04143290-itera-limited |archive-date=2017-01-18 -->}}</ref>
<ref name="NEXOK_Itera">{{cite web |title=Itera Limited |publisher=NEXOK |url=https://www.nexok.co.uk/company/04143290/itera-limited |access-date=2017-01-18}}</ref>
<ref name="realng">REAL/NG main page (2001) ([https://web.archive.org/web/20011103183717/http://www.realng.com/]).</ref>
<ref name="keyfeaturesofrealng">Key features of REAL/NG (2003) ([https://web.archive.org/web/20030810131406/http://www.realng.com/keyfeaturesofrealng.htm from realng.com 2003]).</ref>
<ref name="realng_probablylatest">Probably latest REAL/NG ([https://web.archive.org/web/20031224153358/http://www.realng.com/ realng.com 2003]).</ref>
<ref name="realng_disappear">REAL/NG disappearing from realng.com ([https://web.archive.org/web/20050130075440/http://realng.com/ realng.com 2005]).</ref>

</references>

==Further reading==
* {{cite web |title=DRTIPS.ZIP |date=1993-01-07 |orig-year=1992 |author=[[Novell Desktop Systems Group]] |publisher=[[Digital Research]] / [[Novell]] |url=https://www.pcorner.com/list/AOS/DRTIPS.ZIP/INFO/ |access-date=2018-04-03 |url-status=live |archive-url=https://archive.today/20180912215956/https://www.pcorner.com/list/AOS/DRTIPS.ZIP/INFO/ |archive-date=2018-09-12}}

==External links==
* [https://web.archive.org/web/20190401161050/http://www.imsltd.com/ former Intelligent Micro Software (IMS) website (vendors of IMS Multiuser DOS, IMS REAL/32, and REAL/NG)]
* [https://web.archive.org/web/20010515195706/http://www.lii.com/ former Logan Industries (LLI) website (IMS REAL/32 US distributor up to 2002-05-01)]
* [https://web.archive.org/web/20071213140207/http://www.conctrls.com/ former Concurrent Controls website (CCI Multiuser DOS)]
* [https://web.archive.org/web/*/https://applica.com Applica, Inc. website]
* [https://web.archive.org/web/20040412051935/http://www.aplycon.com/ former Aplycon Technologies, Inc. website]

{{Digital Research}}
{{Disk operating systems}}

[[Category:CP/M variants]]
[[Category:Disk operating systems]]
[[Category:DOS variants]]
[[Category:Real-time operating systems]]
<!-- [[Category:Digital Research]]-->
[[Category:Digital Research operating systems]]
[[Category:Novell operating systems]]
[[Category:Microcomputer software]]
[[Category:Discontinued operating systems]]
[[Category:Proprietary operating systems]]