View source for DOS Plus

{{Short description|Discontinued computer operating system for x86 processors}}
{{Use dmy dates|date=April 2019|cs1-dates=y}}
{{Use list-defined references|date=December 2021}}
{{Infobox OS
| name                   = DOS Plus<!-- Name of program or distribution -->
| logo                   = <!-- filename only (no wikilink, no Image:/File:) -->
| logo caption           = 
| logo size              = 
| logo alt               = 
| screenshot             = Digital Research DOS Plus Version 1.2 720x400.png<!-- filename only (no wikilink, no Image:/File:) -->
| caption                = Digital Research DOS Plus Version 1.2
| screenshot_size        = 
| screenshot_alt         = 
| collapsible            = 
| version of             = <!-- For articles about releases of operating systems ONLY -->
| developer              = [[Digital Research]]<!-- Name of main developer or sponsor-->
| family                 = [[CP/M-86]]<!-- "Unix-like" or "Microsoft Windows" -->
| working state          = Discontinued<!-- "Current", "Discontinued" (operating systems), or "No longer supported" (releases) -->
| source model           = [[Closed source]]<!-- "Open source", "Closed source", or "Shared source" -->
| released               = {{Start date and age|1985|df=yes}}
| discontinued           = <!-- DON'T use this for articles about releases of operating systems -->
| RTM date               = <!-- {{Start date and age|YYYY|MM|DD|df=yes}} ONLY for articles about OS releases -->
| GA date                = <!-- {{Start date and age|YYYY|MM|DD|df=yes}} ONLY for articles about OS releases -->
| latest release version = DOS Plus 2.1 (with [[Basic Disk Operating System|BDOS]] 5.0)
| latest release date    = 
| latest preview version = 
| latest preview date    = <!-- {{Start date and age|YYYY|MM|DD|df=yes}} -->
| marketing target       = 
| programmed in          = 
| language               = [[English language|English]]<!-- Supported human languages (English, French, Italian, Arabic, …) -->
| update model           = <!-- APT, Windows Update, etc. -->
| package manager        = <!-- dpkg, rpm, Windows installer, etc. -->
| supported platforms    = [[Intel 8086]], [[Intel 80186]]<!-- IA-32, x64, Itanium, ARM, etc. -->
| kernel type            = [[Monolithic kernel]]<!-- Hybrid, Monolithic, Microkernel, Exokernel, Nanokernel, etc. -->
| userland               = 
| ui                     = [[Command-line interface]] ([[COMMAND.COM]])
| license                = [[Proprietary software|Proprietary]]
| preceded by            = [[CP/M-86 Plus]]
| succeeded by           = [[DR&nbsp;DOS]]
| website                = <!-- {{URL|www.example.org}} -->
| support status         = <!-- For articles about releases of operating systems ONLY -->
| other articles         = 
| prog_language          = 
}}

'''DOS&nbsp;Plus''' (erroneously also known as '''DOS+''') was the first [[operating system]] developed by [[Digital Research]]'s OEM Support Group<ref name="Wein_2009_DOSPLUS"/> in [[Newbury, Berkshire]], UK, first released in 1985. DOS&nbsp;Plus 1.0 was based on [[CP/M-86 Plus]] combined with the [[PCMODE]] emulator from [[Concurrent PC&nbsp;DOS 4.11]].<ref name="Wein_2009_DOSPLUS"/> While CP/M-86 Plus and [[Concurrent DOS 4.1]] still had been developed in the United States, Concurrent PC&nbsp;DOS 4.11 was an internationalized and bug-fixed version brought forward by Digital Research UK.<ref name="Wein_2009_DOSPLUS"/> Later DOS&nbsp;Plus 2.x issues were based on [[Concurrent PC&nbsp;DOS 5.0]] instead. In the broader picture, DOS Plus can be seen as an intermediate step between [[Concurrent CP/M-86]] and [[DR&nbsp;DOS]].

DOS&nbsp;Plus is able to run programs written for either CP/M-86 or [[MS-DOS 2.11]], and can read and write the floppy formats used by both of these systems. Up to four CP/M-86 programs can be [[computer multitasking|multitasked]], but only one [[DOS]] program can be run at a time.

=={{anchor|FIDDLOAD}}User interface==
DOS&nbsp;Plus attempts to present the same [[command-line interface]] as MS-DOS. Like MS-DOS, it has a [[command-line interpreter]] called <code>[[COMMAND.COM]]</code> (alternative name <code>DOSPLUS.COM</code>). There is an <code>[[AUTOEXEC.BAT]]</code> file, but no <code>[[CONFIG.SYS]]</code> (except for FIDDLOAD, an extension<!-- parsing a CONFIG.SYS file --> to load some field-installable [[device driver]]s (FIDD) in some versions of DOS&nbsp;Plus 2.1<!-- at least the version for the BBC Master 512 -->). The major difference the user will notice is that the bottom line of the screen contains status information similar to:

 DDT86    ALARM                  UK8 PRN=LPT1      Num    10:17:30

The left-hand side of the status bar shows running [[process (computing)|processes]]. The leftmost one will be visible on the screen; the others (if any) are running in the background. The right-hand side shows the keyboard layout in use (UK8 in the above example), the printer port assignment, the keyboard [[Caps Lock]] and [[Num Lock]] status, and the current time. If a DOS program is running, the status line is not shown. DOS programs cannot be run in the background.

The keyboard layout in use can be changed by pressing {{keypress|[[Control key|Ctrl]]}}, {{keypress|[[Alt key|Alt]]}} and one of the [[function key]]s {{keypress|F1}}–{{keypress|F5}}.

=={{anchor|BACKG|SLICE}}Commands==
DOS&nbsp;Plus contains a number of extra [[command (computing)|commands]] to support its multitasking features:

* ADDMEM: Sets the amount of extra memory to allocate to [[.exe|EXE]] programs.
* ALARM: A message alarm clock.
* BACKG: Allows [[background process]]es to be listed and stopped.
* COMSIZE: Sets the amount of memory to allocate to [[COM file|COM]] programs.
* [[PRINT (command)|PRINT]]: [[Print_spooling|Print spooler]].
* SLICE: Sets the amount of processor time to give to the foreground program. See also the [[%$SLICE%]] environment variable.<ref name="Kotulla_1987_Environment"/><ref name="Paul_2002_CLS"/>
* USER: Sets the user number to use when accessing CP/M media.

It also contains subsets of the standard [[List of DOS commands|DOS command]]s and CP/M commands – for example, it has both a built-in <code>[[COPY (command)|COPY]]</code> command, and a <code>[[Peripheral Interchange Program|PIP]]</code> utility, both of which copy files.

The <code>[[CD (command)|CD]]</code> command can assign one of the three drives N:, O: or P: to a directory on a different drive, in a similar manner to the MS-DOS command <code>[[SUBST]]</code>. For example,

 CD N:=C:\DATA\ACCOUNTS

will cause the directory <code>C:\DATA\ACCOUNTS</code> to appear as drive N:. This so-called ''[[floating drive]]'' feature allows old programs which don't support [[subdirectories]] to work under DOS&nbsp;Plus and can be used to make file handling at the [[command prompt]] much easier.
This feature is also present in [[Concurrent DOS]], [[Multiuser DOS]], System Manager 7, and [[REAL/32]], however, these systems extend the concept to all unused drive letters from A: to Z:, except for drive letter L:. [[DR&nbsp;DOS]] 3.31 – 6.0 (up to the November 1992 updates with [[Basic Disk Operating System|BDOS]] 6.7 only<!-- BDOS 7.0 (PalmDOS), BDOS 7.1 (DR DOS 6.0 business update) and higher no longer support this -->) also support this (including drive letter L:). Under the later systems, the [[4DOS]]/[[NDOS]] command processor supports this features as well.<ref name="4DOS_8.00_HELP"/> Floating drives are implemented in the BDOS kernel, not in the command line shell, thus this feature can also be used from within DOS applications when entering [[path (computing)|directory paths]] for as long as the application does not parse and split the dirspec for further processing.

Using a similar feature, <!-- not sure about DOS Plus!--> Concurrent DOS<!-- at least Concurrent DOS XM and Concurrent DOS 386 since 1987 -->, Multiuser DOS, System Manager and REAL/32 will dynamically assign a floating drive L: to the load path of a loaded application, thereby allowing applications to refer to files residing in their load directory under a standardized drive letter instead of under a fixed absolute path. This ''[[load drive]]'' feature makes it much easier to move software installations on and across disks without having to adapt paths to overlays, configuration files or user data stored in the load directory or subsequent directories. (For similar reasons, the appendage to the environment block associated with loaded applications under MS-DOS/PC&nbsp;DOS 3.0 (and higher) contains a reference to the load path of the executable, however, this consumes more resident memory, and to take advantage of it, support for it must be coded into the executable, whereas DRI's solutions transparently works with any kind of application.)

Another feature resulting from the BDOS' internal organization of current working directories as relative links to parent directories is the theoretically unlimited directory depth supported by all those above mentioned operating systems – in contrast to MS-DOS/PC&nbsp;DOS (and DR&nbsp;DOS since 1992), where an MS-DOS compatible internal data structure named [[Current Directory Structure]] (CDS) limits directory depths to a maximum of 66 characters.

These features can be attributed to the fact that CP/M itself did not have a concept of subdirectories, and DOS was emulated under these operating systems, so directories had to be translated to internal CP/M structures in some intelligent way.

==Internal structure==
DOS&nbsp;Plus boots from a single file called either DOSPLUS.SYS or NETPLUS.SYS (rather than the [[IO.SYS]] / [[MSDOS.SYS]] combination of MS-DOS). This file is in the CP/M-86 [[CMD file (CP/M)|CMD]] format, and is structured internally as a number of modules:

* The [[CP/M#Basic Disk Operating System|BDOS]] basic disk operating system [[kernel (operating system)|kernel]], which handles multitasking and implements the CP/M [[application programming interface|API]].
* The [[XIOS]] extended input/output system, which is the [[machine-dependent software|machine-dependent]] component that performs low-level disc and character I/O.
* In the case of NETPLUS.SYS with DR&nbsp;Net support.
* The DOS [[emulator]] (internally named [[PCMODE]]), which converts each MS-DOS function call into one or more CP/M calls. In the case of a request to change the current directory, for example, this would translate to a series of 'open directory' calls, one for each directory in the provided path.
* A stub which loads COMMAND.COM (or DOSPLUS.COM) when required. This stub contains the string "[[%OS%|OS]]=CPCDOS",<ref name="Paul_2002_OS"/><ref name="Paul_1997_NWDOSTIP"/> suggesting that it is based on the [[Concurrent PC&nbsp;DOS]] codebase.

==Computers that used DOS Plus==
DOS&nbsp;Plus was the main operating system in ROM for the [[Philips :YES]], for which it was originally developed.<ref name="Wein_2009_DOSPLUS"/><ref group="nb" name="NB1_ROM"/> [[IBM PC compatible|PC compatible]] versions were supplied with the [[Amstrad PC1512]]<ref name="Wein_2009_DOSPLUS"/> and the Jasmin Turbo from the French company T.R.A.N.&nbsp;S.A.<!-- "T.R.A.N." (S.A.) was sometimes spelled "TRAN" and "Tran" --><ref name="TRAN_1987_Jasmin"/><ref name="Halbra_1987_Jasmin"/> The non-IBM PC compatible [[BBC Master 512]],<ref name="Burton_1989_DOSPlus"/> came with DOS&nbsp;Plus 1.2, 1.2a or 2.1,<ref name="YP_Master_512"/><ref name="Snee_1989"/> also in conjunction with Solidisk's PC&nbsp;Plus memory expansion.<ref name="YP_Master_512"/><ref name="Snee_1989"/> There were DOS&nbsp;Plus 2.1e/g adaptations for the [[Apricot ACT]] series' non-standard [[File Allocation Table#Exceptions|315&nbsp;KB]] and [[File Allocation Table#Exceptions|720&nbsp;KB]] [[FAT12]] floppy formats. The [[logical sectored FAT]] hard disk format (partition type {{mono|[[Partition type#PID_F2h|0xF2]]}}) of [[Sperry IT]] PCs, and the 80186 [[floating-point unit|co-processor]] boards for the [[Acorn Archimedes A300]] and [[Acorn Archimedes A310|A310]] as well as [[Acorn 286]] prototypes<!-- at least I am not aware of released Acorn 286 --> were supported as well.

=={{anchor|1.0|1.1|1.2|1.2a|2.1}}Versions==
Known operating system versions include:

* DOS&nbsp;Plus 1.0 (ROMed in [[Philips :YES]]) (with BDOS 4.1).<ref group="nb" name="NB1_ROM"/>
* DOS&nbsp;Plus 1.1<ref name="Yes_1985_DOSPLUS11"/> (with BDOS 4.1)
* DOS&nbsp;Plus 1.2 (with BDOS 4.1)
* DOS&nbsp;Plus 2.1 (with BDOS 5.0)<ref name="Burton_1989_DOSPlus"/>

==See also==
* [[Personal CP/M-86 2.0]] (with BDOS 4.1)
* [[Personal CP/M-86 2.11]] (with BDOS 4.1)
* [[CP/M-86 Plus]]
* [[MSX-DOS]]
* [[GEMDOS]]
* [[GEM XM]]

==Notes==
{{Reflist|group="nb"|refs=
<ref group="nb" name="NB1_ROM">This version does not implement the S_OSVER call and thus cannot be queried for its actual version number.</ref>
}}

==References==
{{Reflist|refs=
<ref name="Wein_2009_DOSPLUS">{{cite web |title=DRI History and Joe Wein |author-first=Josef "Joe" |author-last=Wein |editor-first=Herbert R. |editor-last=Johnson |date=2010-02-19 |orig-date=November 2009 |url=http://retrotechnology.com/dri/dri_wein.html |access-date=2017-01-17 |url-status=live |archive-url=https://web.archive.org/web/20170117185919/http://retrotechnology.com/dri/dri_wein.html |archive-date=2017-01-17}}</ref>
<ref name="Yes_1985_DOSPLUS11">{{cite book |author=((:Yes product management)) |title=README file for :YES Release 2 - DOS Plus 1.1 maintenance version |type=README.DOS file on maintenance disk |publisher=[[Philips Austria]] |date=1985 |quote=This file contains additional information on the use of DOS&nbsp;Plus 1.1 on the [[Philips :YES|:YES]] Rel&nbsp;1 and :YES Rel&nbsp;2.}}</ref>
<ref name="Paul_2002_OS">{{cite web |title=How to detect FreeCOM/FreeDOS in-batch? |author-first=Matthias R. |author-last=Paul |date=2002-02-20 |publisher=freedos-dev mailing list |url=http://marc.info/?l=freedos-dev&m=101423986407077&w=2 |access-date=2014-08-06 |url-status=live |archive-url=https://archive.today/20140812042828/http://marc.info/?l=freedos-dev&m=101423986407077&w=2 |archive-date=2014-08-12}}</ref>
<ref name="Paul_1997_NWDOSTIP">{{cite web |title=NWDOS-TIPs &mdash; Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds |work=MPDOSTIP |author-first=Matthias R. |author-last=Paul |date=1997-07-30 |orig-date=1994-05-01 |edition=3 |version=Release 157 |language=de |url=http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |access-date=2014-08-06 |url-status=live |archive-url=https://web.archive.org/web/20161104235829/http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |archive-date=2016-11-04}} (NB. NWDOSTIP.TXT is a comprehensive work on [[Novell DOS 7]] and [[OpenDOS 7.01]], including the description of many undocumented features and internals. It is part of the author's yet larger <code>MPDOSTIP.ZIP</code><!-- still named TIPS_MP.ZIP between 1991 and 1996-11 --> collection maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the <code>NWDOSTIP.TXT</code> file.) [https://web.archive.org/web/20190601152204/https://www.sac.sk/download/text/mpdostip.zip<!-- A yet older version 155 from 1997-05-13 of the 1997-07-15 distribution archive. -->]</ref>
<ref name="Paul_2002_CLS">{{cite web |title=Updated CLS posted |author-first=Matthias R. |author-last=Paul |date=2002-03-26 |url=http://marc.info/?l=freedos-dev&m=101717593306186&w=2 |publisher=freedos-dev mailing list |access-date=2014-08-06 |url-status=live |archive-url=https://web.archive.org/web/20181004145539/https://marc.info/?l=freedos-dev&m=101717593306186&w=2 |archive-date=2018-10-04}}</ref>
<ref name="Burton_1989_DOSPlus">{{cite book |title=Master 512 Technical Guide |chapter=Introduction - Purpose and Scope |author-first=Robin |author-last=Burton |publisher=[[Dabs Press]] |publication-place=Prestwich, Manchester, UK |location=Leicestershire, UK |date=September 1989 |url=http://bbc.nvg.org/doc/Master%20512%20Technical%20Guide/m512techintro.htm |access-date=2018-05-09 |url-status=live |archive-url=https://web.archive.org/web/20081204161210/http://bbc.nvg.org/doc/Master%20512%20Technical%20Guide/m512techintro.htm |archive-date=2008-12-04 |quote=[…] We are unable to reproduce the source code for any of the versions of DOS&nbsp;Plus as used by the [[BBC Master 512|512]]. The material is the property and copyright of [[Digital Research]], not of [[Acorn Computers]]. This is further complicated by the fact that four different versions have actually been issued. […] There have been several versions of DOS&nbsp;Plus for the 512, version 2.1 being the latest issue. […]}} [https://web.archive.org/web/20230820172841/https://acorn.huininga.nl/pub/docs/manuals/Acorn/80186%20Second%20Processor/Master%20512%20Technical%20Guide.pdf]</ref>
<ref name="YP_Master_512">{{cite web |work=Yellow Pig's BBC Computer Pages |title=The BBC Master 512 - DOS-Plus and GEM System Software |url=http://www.cowsarenotpurple.co.uk/bbccomputer/master512/system.html |access-date=2018-05-20 |url-status=live |archive-url=https://web.archive.org/web/20180520125830/http://www.cowsarenotpurple.co.uk/bbccomputer/master512/system.html |archive-date=2018-05-20}}</ref>
<ref name="Snee_1989">{{cite book |title=Master 512 User Guide |author-first=Chris |author-last=Snee |publisher=[[Dabs Press]] |chapter=Chapter 6. Permanent commands |date=1989-03-05 |isbn=1870336143 |url=http://www.cowsarenotpurple.co.uk/bbccomputer/master512/m512ug-dabs/chap06.html |access-date=2018-05-20 |url-status=live |archive-url=https://web.archive.org/web/20180520131235/http://www.cowsarenotpurple.co.uk/bbccomputer/master512/m512ug-dabs/chap06.html |archive-date=2018-05-20}}</ref>
<ref name="Kotulla_1987_Environment">{{cite journal |title=Von CP/M zu MS-DOS, Teil 11 |language=de |author-first=Martin |author-last=Kotulla |author-link=Martin Kotulla |journal=Professional Computing (PC) - Schneider International |volume=3 |issue=11 |date=November 1987 |pages=100–103 |url=http://www.homecomputerworld.at/magazine/cpc/CPCAI-87-11.pdf |access-date=2018-05-20 |url-status=live |archive-url=https://web.archive.org/web/20190424201007/http://www.homecomputerworld.at/magazine/cpc/CPCAI-87-11.pdf |archive-date=2019-04-24}}</ref>
<ref name="TRAN_1987_Jasmin">{{cite magazine |title=Les compatibles PC professionneles et télématiques les plus vendus: les Jasmins Turbo HQ de TRAN |language=fr |type=Advertisement |magazine=[[Micro Systèmes]] |issn=0183-5084 |publisher=[[Société Parisienne d'Édition]] |location=[[La Valette-du-Var]], France |publication-place=Paris, France |date=February 1987 |number=72 |pages=12–13 |url=http://fr.1001mags.com/parution/micro-systemes/numero-72-fevrier-1987/page-12-13-texte-integral |access-date=2020-02-17 |url-status=live |archive-url=https://archive.today/20200217164525/http://fr.1001mags.com/parution/micro-systemes/numero-72-fevrier-1987/page-12-13-texte-integral |archive-date=2020-02-17 |quote=[…] Jasmin Turbo […] les systèmes d'exploitation DOS PLUS et [[GEM (desktop environment)|GEM]] de D.R.I. avec le guide et les licences officielles […] Systèmes d'exploitation J'ai apprécié le choix du système d'exploitation DOS&nbsp;PLUS de [[Digital Research Inc.]], pour sa double compatibilité avec le système [[MS-DOS 2.11]] et [[CP/M-86]]. Vive les transferts de fichiers entre les deux standards. Le système d'exploitation d'environnement graphique G.E.M. […] de DRI est livré avec, ce qui permet à JASMIN TURBO d'utiliser toute application écrite sous GEM, disponible sur le marché. Par exemple, le GEM-DESKTOP (pour BUREAU) permet d'utiliser le JASMIN TURBO avec des Icônes comme un [[Apple Macintosh|Macintosh]]. […]}}</ref>
<ref name="Halbra_1987_Jasmin">{{cite magazine |title=GRAPHISTE … et le Jasmin HQ-20 dessine - Le PC voit rouge vert, bleu … |language=fr |author-first=Yves |author-last=Halbra |magazine=[[Tilt (French magazine)|Tilt]] |series=Compatibles PC |issn=0753-6968 |publisher={{ill|Editions Mondiales{{!}}Editions Mondiales S.A.|fr|Editions Mondiales}} |publication-place=Paris, France |number=6 |date=October 1987 |pages=32, 34, 52–53, 142–143, 173 |url=https://archive.org/details/TiltHS1987-06/mode/2up |access-date=2020-02-17 |url-status=live |archive-url=https://web.archive.org/web/20200217175501/https://archive.org/details/TiltHS1987-06 |archive-date=2020-02-17 |quote=[…] Système d'exploitation: DOS-Plus et MS-DOS 2.11. […]}} [https://archive.org/stream/TiltHS1987-06/TiltHS1987-06_djvu.txt][https://archive.org/download/TiltHS1987-06/TiltHS1987-06.pdf]</ref>
<ref name="4DOS_8.00_HELP">{{cite book |title=4DOS 8.00 online help |title-link=4DOS 8.00 |author-first1=Hardin |author-last1=Brothers |author-first2=Tom |author-last2=Rawson |author-link2=Tom Rawson |author-first3=Rex C. |author-last3=Conn |author-link3=Rex C. Conn |author-first4=Matthias R. |author-last4=Paul |author-first5=Charles E. |author-last5=Dye |author-first6=Luchezar I. |author-last6=Georgiev |date=2002-02-27}}</ref>
}}

==Further reading==
* {{cite book |author-last=Gilmour |author-first=Jean |date=1986 |title=Amstrad Personal Computer PC1512 User Instructions}}
* {{cite book |author-last=Morris |author-first=Stephen |date=1986 |series=Digital Research books |publisher=Glentop Publishers Ltd. |title=Using DOS Plus on the Amstrad PC |isbn=1-85181-063-3}}

==External links==
* http://bbc.nvg.org/doc/Master%20512%20Technical%20Guide/

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

[[Category:CP/M variants]]
[[Category:Microcomputer software]]
<!-- [[Category:Digital Research]] -->
[[Category:Disk operating systems]]
[[Category:Floppy disk-based operating systems]]
[[Category:Embedded operating systems]]
[[Category:ROM-based operating systems]]
[[Category:DOS variants]]
[[Category:Digital Research operating systems]]
[[Category:Discontinued operating systems]]
[[Category:Assembly language software]]
[[Category:1985 software]]