Editing Multiuser DOS (section)

=={{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.

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"/>