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((About|the operating system of the Atari 8-bit computers|the Atari ST's operating system|Atari TOS))
((About||the MS-DOS compatible operating system of the Atari Portfolio|DIP DOS))
((Redir|MyDOS|the similarly pronounced Microsoft operating system|MIDAS (operating system)((!))MIDAS))
((Redir|RealDOS|the similarly named successor to Multiuser DOS|IMS REAL/32))
((Redir|Turbo-DOS|the CP/M-compatible operating system|Software 2000 TurboDOS))
((More citations needed|date=March 2020))

((Infobox OS
|name = Atari DOS
|logo =
|screenshot = Ataridos-2.5.PNG
|caption = Atari DOS version 2.5, main menu
|developer = [[Atari, Inc.]], [[Atari Corporation]]
|source_model = [[Closed source]]
|kernel_type =
|supported_platforms = [[Atari 8-bit family]]
|ui = Menu
|family =
|released = ((Start date and age|1979))
|latest_release_version = XE 1.0
|latest_release_date = ((Start date and age|1987))
|latest_test_version =
|latest_test_date =
|marketing_target =
|programmed_in =
|prog_language =
|language = [[English language|English]]
|updatemodel =
|package_manager =
|working_state = Discontinued
|license = [[Proprietary software|Proprietary]] [[EULA]]
|website =
))

'''Atari DOS''' is the [[disk operating system]] used with the [[Atari 8-bit family]] of computers. [[Operating system]] extensions loaded into memory were required in order for an Atari computer to manage files stored on a [[Disk storage|disk drive]]. These extensions to the operating system added the disk handler and other file management features.

((anchor|FMS))The most important extension is the disk handler. In Atari DOS 2.0, this was the '''File Management System''' ('''FMS'''), an implementation of a [[file system]] loaded from a [[floppy disk]]. This meant at least an additional ((nowrap|32 KB)) [[random-access memory|RAM]] was needed to run with DOS loaded.

==Versions==
There were several versions of Atari DOS available, with the first version released in 1979.<ref>[http://www.oshistory.net/metadot/index.pl?id=2583;isa=Category;op=show Atari]  ((webarchive|url=https://web.archive.org/web/20090221201218/http://www.oshistory.net/metadot/index.pl?id=2583%3Bisa%3DCategory%3Bop%3Dshow |date=February 21, 2009 ))</ref> Atari was using a [[cross assembler]] with [[Data General AOS]].

===((anchor|1))DOS 1.0===
In the first version of DOS from [[Atari]] all commands were only accessible from the menu. It was bundled with the ''[[Atari 810|810]]'' disk drives. This version was entirely memory resident, which made it fast but occupied memory space.

===((anchor|2.0S|2.0D))DOS 2.0===
:Also known as ''DISK OPERATING SYSTEM II VERSION 2.0S''
The second, more popular version of DOS from Atari was bundled with the ''810'' disk drives and some early ''[[Atari 1050|1050]]'' disk drives. It is considered to be the [[lowest common denominator]] for Atari DOSes, as any Atari-compatible disk drive can read a disk formatted with ''DOS 2.0S''.

''DOS 2.0S'' consisted of <code>DOS.SYS</code> and <code>DUP.SYS</code>. <code>DOS.SYS</code> was loaded into memory, while <code>DUP.SYS</code> contained the disk utilities and was loaded only when the user exited to DOS.

In addition to bug fixes, ''DOS 2.0S'' featured improved <code>NOTE/POINT</code> support and the ability to automatically run an Atari [[executable]] file named <code>AUTORUN.SYS</code>. Since user memory was erased when <code>DUP.SYS</code> was loaded, an option to create a <code>MEM.SAV</code> file was added. This stored user memory in a temporary file (<code>MEM.SAV</code>) and restored it after <code>DUP.SYS</code> was unloaded. The previous menu option from ''DOS 1.0'', <code>N. DEFINE DEVICE</code>, was replaced with <code>N. CREATE MEM.SAV</code> in ''DOS 2.0S''.

Version ''2.0S'' was for [[#Disk formats|single-density]] disks, ''2.0D'' was for [[#Disk formats|double-density]] disks. 2.0D shipped with the ''[[Atari 815|815]]'' Dual Disk Drive, which was both expensive and incompatible with the standard 810, and thus sold only a small number; making DOS version ''2.0D'' rare and unusual.

===((anchor|3))DOS 3===
[[File:Atari Master Diskette 3 DOS 3 Floppy Disk in Sleeve.jpg|thumb|DOS 3 diskette as supplied with a 1050 disk drive]]
A new version of DOS that came originally bundled with the 5.25-inch [[Atari 1050]] disk drive. This made use of the new ''[[#Disk formats|Enhanced Density]]'' (ED)((efn|Not to be confused with the much later ''extra-high density'' (ED) [[perpendicular recording]] floppy disks.)) capability, also referred to by Atari as ''Dual Density''. This increased storage from 88 KB to 130 KB per disk. There was a single density (88 KB) formatting option to maintain compatibility with older Atari 810 disk drives.

By organizing [[Disk sector|sector]]s into [[Block (data storage)|blocks]], Atari was anticipating larger capacity floppy disks, but this resulted in incompatibility with ''DOS 2.0S''. Files converted to DOS 3 could not be converted back to ''DOS 2.0''. As a result, DOS 3 was extremely unpopular and did not gain widespread acceptance amongst the Atari user community.

DOS 3 provided built-in help via the Atari HELP key and/or the inverse key. Help files needed to be present on the system DOS disk to function properly. DOS 3 also used special XIO commands to control disc operations within BASIC programs.

===((anchor|2.5))DOS 2.5===
:Also known as ''DISK OPERATING SYSTEM II VERSION 2.5''

Version 2.5 is an upgrade to 3.0.<ref name="chadwick1985">((Cite book |title=Mapping the Atari |last=Chadwick |first=Ian |publisher=Compute! Publications, Inc. |year=1985 |isbn=0-87455-004-1 |location=Greensboro, North Carolina |chapter=Appendix Seventeen: Dos 2.5 And The 1050 Drive |chapter-url=http://www.atariarchives.org/mapping/appendix17.php))</ref> After listening to complaints by their customers, Atari released an improved version of their previous DOS. This allowed the use of Enhanced Density disks, and there was a utility to read DOS 3 disks. An additional option was added to the menu (<code>P. FORMAT SINGLE</code>) to format single-density disks. DOS 2.5 was shipped with ''1050'' disk drives and some early ''[[Atari XF551|XF551]]'' disk-drives.

Included utilities were <code>DISKFIX.COM</code>, <code>COPY32.COM</code>, <code>SETUP.COM</code> and <code>RAMDISK.COM</code>.

===((anchor|QDOS))DOS 4.0===
:Codename during production: ''QDOS''
DOS 4.0 was designed for the never-released ''[[Atari 1450XLD|1450XLD]]''. The rights were returned to the author, Michael Barall, who placed it in the [[public domain]]. It was later published by [[Antic Software]]. DOS 4.0 used blocks instead of single sectors, and supported single, enhanced, and double density, as well as both single- and double-sided drives. DOS 4.0 was not compatible with DOS 2 or 3 disks but could read files from them. It also did not automatically switch densities, and it was necessary to go to the menu and manually select the correct density.

===((anchor|ADOS|XE))DOS XE===
:Codename during production: ADOS
DOS XE supported the [[#Disk formats|double-density]] and double-sided capabilities of the [[Atari XF551]] drive, as well as its burst I/O. DOS XE used a new disk format which was incompatible with DOS 2.0S and DOS 2.5, requiring a separate utility for reading older 2.0 files. It also required [[Bank switching|bank-switched]] RAM, so it did not run on the 400/800 machines. It supported date-stamping of files and sub-directories.

DOS XE was the last DOS made by Atari for the Atari 8-bit family.

==Third-party DOS programs==
Many of these DOSes were released by manufacturers of third-party drives, anyone who made drive modifications, or anyone who was dissatisfied with the available DOSes. Often, these DOSes could read disks in higher densities, and could set the drive to read disks faster (using ''Warp Speed'' or ''Ultra-Speed'' techniques). Most of these DOSes (except SpartaDOS) were DOS 2.0 compatible.

===SmartDOS===
Menu driven DOS that was compatible with DOS 2.0. Among the first third-party DOS programs to support [[#Disk formats|double-density]] drives.

Many enhancements including sector copying and verifying, speed checking, turning on/off file verifying and drive reconfiguration.

Published by Rana Systems. Written by John Chenoweth and Ron Bieber, last version 8.2D.

===OS/A+ and DOS XL===
DOS produced by [[Optimized Systems Software]]. Compatible with DOS 2.0 - Allowed the use of Double Density floppies. Unlike most ATARI DOSses, this used a [[Command-line interface|command line]] instead of a menu. [[DOS XL]] provided a menu program in addition to the command line.

===SuperDOS===
This DOS could read SS/SD, SS/ED, SS/DD and DS/DD disks, and made use of all known methods of speeding up disk-reads supported by the various third-party drive manufacturers.

Published by Technical Support((clarification needed|date=September 2016)). Written by Paul Nicholls.

===Top-DOS===
Menu driven DOS with enhanced features. Sorts disk directory listings and can set display options. File directory can be [[data compression|compressed]]. Can display deleted files and undelete them. Some advanced features required a proprietary TOP-DOS format.

Published by Eclipse Software. Written by R. K. Bennett.

===Turbo-DOS===
This DOS supports Turbo 1050, Happy, Speedy, XF551 and US Doubler highspeed drives. XL/XE only.

Published by Martin Reitershan Computertechnik. Written by Herbert Barth and Frank Bruchhäuser.

===MyDOS===
This DOS adds the ability to use sub-directories, and supports hard-drives.

Published by Wordmark Systems, includes complete [[source code]].

===SpartaDOS===
This DOS used a command-line interface. Was not compatible with DOS 2.0, but could read DOS 2.0 disks. Supports [[subdirectories]] and [[hard drives]] being capable of handling filesystems sized up to 16 [[megabyte|MB]]. Included the capability to create primitive batch files.

====SpartaDOS X====
[[File:SpartaDOS X prompt.png|thumb|350px|Screenshot of SpartaDOS X by FTE & DLT]]
((main|SpartaDOS X))
A more sophisticated version of [[SpartaDOS]], which strongly resembles MS-DOS in its look and feel. It was shipped on a 64 KB [[ROM cartridge]].

====RealDOS====
A SpartaDOS compatible DOS (in fact, a renamed version of SpartaDOS 3.x, due to legal reasons).

''RealDOS'' is [[shareware]] by Stephen J. Carden and Ken Ames.

===BW-DOS===
[[File:Bwdos.png|thumb|350px|Screenshot of BW-DOS by Jiří Bernasek]]
A SpartaDOS compatible DOS, the last version 1.30 was released in December 1995. It has a much lower [[memory footprint]] compared to the original SpartaDOS and does not use the RAM under the [[read only memory|ROM]] of XL/XE machines, allowing it to be used on the older [[Atari 400]]/[[Atari 800|800]] models.

BW-DOS is [[freeware]] by Jiří Bernasek.

===XDOS===
XDOS is freeware by Stefan Dorndorf.

==Disk formats==
A number of different formats existed for Atari disks. Atari DOS 2.0S, single-sided, single-density disk had 720 sectors divided into 40 [[Track (disk drive)|tracks]]. After [[Disk formatting|formatting]], 707 sectors were free. Each 128-byte sector used the last 3 bytes for [[Housekeeping (computing)|housekeeping]] data (bytes used, file number, next sector), leaving 125 bytes for data. This meant each disk held 707 × 125 = 88,375 bytes of user data.

The single-density disk holding a mere 88 KB [[floppy disk|per side]] remained the most popular Atari 8-bit disk format throughout the series' lifetime, and almost all commercial software continued to be sold in that format (or variants of it modified for [[copy protection]]), since it was compatible with all Atari-made disk drives.

* ''Single-Sided, Single-Density'': 40 tracks with 18 sectors per track, 128 bytes per sector. 720 sectors, 90 KB capacity.
* ''Single-Sided, Enhanced-Density'': 40 tracks with 26 sectors per track, 128 bytes per sector. 1040 sectors, 130 KB capacity. Readable by the 1050 and the XF551.
* ''Single-Sided, Double-Density'': 40 tracks with 18 sectors per track, 256 bytes per sector. 720 sectors, 180 KB capacity. Readable by the XF551, the 815, or modified/upgraded 1050.
* ''Double-Sided, Double-Density'': 80 tracks (40 tracks per side) with 18 sectors per track, 256 bytes per sector. 1440 sectors (720 sectors per side), 360 KB capacity. Readable by the XF551 only.

===Percom standard===
In 1978, [[Percom]] established a double-density layout standard which all other manufacturers of Atari-compatible disk drives such as [[Indus GT|Indus]], [[Amdek]], and Rana —except Atari itself— followed. A configuration block of 12 bytes defines the disk layout.<ref name="wilkinson198510">((cite news | url=https://archive.org/stream/1985-10-compute-magazine/Compute_Issue_065_1985_Oct#page/n111/mode/2up | title=Atari Disk Drive Compatibility | work=Compute! | date=October 1985 | access-date=16 October 2013 | author=Wilkinson, Bill | pages=110–111))</ref>

==References==
((reflist))
;Notes
((notelist))
((refbegin))
* ((Citation | author1=Wilkinson, Bill | author2=Compute! Publications, Inc | author3=Optimized Systems Software, Inc | title=Inside Atari DOS | publication-date=1982 | publisher=Compute! Books | isbn=978-0-942386-02-8 )) ([http://www.atariarchives.org/iad/ Online version])
*[http://www.atariarchives.org/mapping/ Mapping the Atari, Revised Edition] by Ian Chadwick
((refend))

==External links==
*[http://www.myoldcomputers.com/museum/man/ataridos3refmanual.htm Atari DOS Reference Manual] ((Webarchive|url=https://web.archive.org/web/20110515101705/http://www.myoldcomputers.com/museum/man/ataridos3refmanual.htm |date=2011-05-15 )) &mdash; Reference manual for DOS 3.
*[http://www.atarimagazines.com/v4n3/AboutDOS.html Antic Vol.4 No.3] Everything You Wanted To Know About Every DOS
*[https://web.archive.org/web/20120316061232/http://atariwiki.strotmann.de/wiki/Wiki.jsp?page=Atari%20DOS%204 Atari Dos 4 (aka ANTIC Dos aka QDOS)] Documentation on Atari DOS 4
*[http://www.wordmark.org/mydos.html MyDOS Source Code] from Wordmark Systems.

((Disk operating systems))

[[Category:Atari 8-bit family software]]
[[Category:Atari operating systems]]
[[Category:Disk operating systems]]
[[Category:Discontinued operating systems]]
[[Category:1979 software]]

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