Atari DOS is the disk operating system used with the
family of computers.
Operating system extensions loaded into memory
were required in order for an
Atari computer to manage files stored on
a disk drive. These extensions to the operating system added the disk
handler and other file management features.
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 32
KB RAM was needed to run with DOS loaded.
1.1 DOS 1.0
1.2 DOS 2.0
1.3 DOS 3
1.4 DOS 2.5
1.5 DOS 4.0
1.6 DOS XE
2 Third-party DOS programs
2.1 DOS 2.6
2.3 OS/A+ and DOS XL
3 Disk formats
5 External links
There were several versions of
Atari DOS available, with the first
version released in 1979.
In the first version of DOS from
Atari all commands were only
accessible from the menu. It was bundled with the 810 disk drives.
This version was entirely memory resident, which made it fast but
occupied memory space.
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 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 DOS.SYS and DUP.SYS. DOS.SYS was loaded into
memory, while DUP.SYS contained the disk utilities and was loaded only
when the user exited to DOS.
In addition to bug fixes, DOS 2.0S featured improved NOTE/POINT
support and the ability to automatically run an
Atari executable file
named AUTORUN.SYS. Since user memory was erased when DUP.SYS was
loaded, an option to create a MEM.SAV file was added. This stored user
memory in a temporary file (MEM.SAV) and restored it after DUP.SYS was
unloaded. The previous menu option from DOS 1.0, N. DEFINE DEVICE, was
replaced with N. CREATE MEM.SAV in DOS 2.0S.
Version 2.0S was for single-density disks, 2.0D was for double-density
disks. 2.0D shipped with the 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.
A new version of DOS that came originally bundled with the 5.25-inch
Atari 1050 disk drive. This made use of the new Enhanced Density (ED)
capability (referred to by
Atari as Dual Density and not to be
confused with later extra-high density (ED) perpendicular recording
floppy disks) offered by the 1050. 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 sectors into 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
Also known as DISK OPERATING SYSTEM II VERSION 2.5
Version 2.5 is an upgrade to 3.0. After listening to complaints by
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 (P. FORMAT SINGLE) to format single-density disks. DOS 2.5 was
shipped with 1050 disk drives and some early XF551 disk-drives.
Included utilities were DISKFIX.COM, COPY32.COM, SETUP.COM and
Codename during production: QDOS
DOS 4.0 was designed for the never-released 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.
Codename during production: ADOS
Atari XF551 drive came out, not only was it Atari's first
drive that could read double-density disks, it was also double-sided.
So support was added in the DOS for double-density and double-sided
A new proprietary disk format made DOS XE incompatible with DOS 2.0S
or DOS 2.5. A separate utility was needed for reading older 2.0 files.
Only XL/XE computers were supported, DOS XE did not work with the
older 400/800 computers due to use of the XL/XE's bank-switching RAM.
DOS XE also supported date-stamping of files, sub-directories and
burst I/O for the XF551 drive.
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.
Someone in the
Atari hacker community[who?] modified DOS 2.0 to add a
few features and allow the use of dual density disk drives, with the
"look and feel" of DOS 2.0. One new feature added was
"RADIX", which one could use to translate hexadecimal numbers to base
10 or base 10 to hex.
Menu driven DOS that was compatible with DOS 2.0. Among the first
third-party DOS programs to support 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 instead of a menu.
DOS XL provided a menu
program in addition to the command line.
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]. Written by Paul
Menu driven DOS with enhanced features. Sorts disk directory listings
and can set display options.
File directory can be 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.
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.
This DOS adds the ability to use sub-directories, and supports
Published by Wordmark Systems, includes complete source code.
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 MB.
Included the capability to create primitive batch files.
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.
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.
SpartaDOS compatible DOS, the last version 1.30 was released in
December 1995. It has a much lower memory footprint compared to the
SpartaDOS and does not use the RAM under the ROM of XL/XE
machines, allowing it to be used on the older
Atari 400/800 models.
BW-DOS is Freeware by Jiří Bernasek.
XDOS is Freeware by Stefan Dorndorf.
A number of different formats existed for
Atari DOS 2.0S,
single-sided, single-density disk had 720 sectors divided into 40
tracks. After formatting, 707 sectors were free. Each 128 byte sector
used the last 3 bytes for housekeeping data (bytes used, file number,
next sector), leaving 125 bytes for data.
The single-density disk holding a mere 88 KB per side remained the
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. 90 KB capacity.
Single-Sided, Double-Density: 40 tracks with 18 sectors per track, 256
bytes per sector. 180 KB capacity. Readable by the XF551, the 815, or
Single-Sided, Enhanced-Density: 40 tracks with 26 sectors per track,
128 bytes per sector. 130 KB capacity. Readable by the 1050 and the
Double-Sided, Double-Density: 80 tracks (40 tracks per side) with 18
sectors per track, 256 bytes per sector. 360 KB capacity. Readable by
the XF551 only.
Percom established a double-density layout standard which all
other manufacturers of Atari-compatible disk drives such as Indus,
Amdek, and Rana—except
Atari itself—followed. A configuration
block of 12 bytes defines the disk layout.
Atari Archived February 21, 2009, at the Wayback Machine.
^ Chadwick, Ian (1985). "Appendix Seventeen: Dos 2.5 And The 1050
Drive". Mapping the Atari. Greensboro, North Carolina: Compute!
Publications, Inc. ISBN 0-87455-004-1.
^ Wilkinson, Bill (October 1985). "
Atari Disk Drive Compatibility".
Compute!. pp. 110–111. Retrieved 16 October 2013.
Wilkinson, Bill; Compute! Publications, Inc; Optimized Systems
Software, Inc (1982), Inside
Atari DOS, Compute! Books,
ISBN 978-0-942386-02-8 (Online version)
Mapping the Atari, Revised Edition by Ian Chadwick
Atari DOS Reference Manual — Reference manual for DOS 3.
Antic Vol.4 No.3 Everything You Wanted To Know About Every DOS
Atari Dos 4 (aka ANTIC Dos aka QDOS) Documentation on
Atari DOS 4
MyDOS Source Code from