Editing Atari DOS (section)

==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]] 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]] 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]]
The 1050 was the first drive from Atari to offer higher recording density. For reasons unknown, they did not take advantage of the 180 kB "double density" mode the hardware in the 1050 was capable of using, and instead introduced a new "Dual Density" mode. To avoid confusion, Atari users soon began referring to this as [[#Disk formats|Enhanced Density]] to differentiate it from real double density systems.

Initially, this increased density mode was not able to be used as Atari shipped the drives with 2.0, which only supported the original 90 kB mode. This was addressed not long after with the release of DOS 3.0. When formatted with DOS 3.0, the disk held 40 tracks of 26 sectors, up from 18 on DOS 2.0. Each sector holds 128 bytes, for a total of 133,120 bytes of storage, up from DOS 2.0's 92,160.

In DOS 2.0, a 10-bit number was used to store sector numbers in the directory. This limited disks to a maximum of 1024 sectors. The new format had 1040 sectors, so 2.0 would not be able to use all of its capability. To address this, and to offer the possibility of working with even larger formats in the future, DOS 3.0 grouped sectors together in groups of eight, known as a [[Block (data storage)|block]], each holding 1,024 bytes. The number in the directory was reduced to 8-bits, meaning it could address up 256 kB on a single disk. The boot information and directory used three blocks, leaving 130 kB free for user storage on the 1050.{{sfn|Wilkinson|1982|p=23}}

Unfortunately, the new directory format made the disks unreadable on DOS 2.0. The DOS 3.0 Master Diskette included a small utility program to copy a 2.0 disk to 3.0, but not one to copy it back. A separate utility allowed disks to be formatted in 2.0 format if compatibility was needed.{{sfn|Wilkinson|1982|p=25}} As a result of this decision, 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 [[Atari 1450XLD|1450XLD]]. It was designed to operate with larger disk formats, adding double density and double sided support while also supporting the older single and enhanced density formats from DOS 2 and 2.5. To support the newer modes, it returned to the blocks concept used in DOS 3.0 when used to format enhanced or double density disks, but this time using slightly smaller 6-sector format, which held 768 bytes in enhanced density and 1536 bytes in double density.

Like DOS 3, disks formatted in the new higher-density formats were not compatible with older drives and DOSes. It could read and write to those disks to retain compatibility. However, it could not determine the format of a disk automatically, and the user had to select the format of the disks from the DOS menu.

The 1450XLD was never released, and the rights for DOS 4 were returned to the author, Michael Barall, who placed it in the [[public domain]]. It was published by [[Antic Software]] in 1984, and is sometimes referred to as "Antic DOS" for this reason.

==={{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 computers.