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.

This meant at least an additional 32 KB RAM was needed to run with DOS loaded.

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.

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.

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.

[3] As a result of this decision, DOS 3 was extremely unpopular and did not gain widespread acceptance amongst the Atari user community.

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.

[4] After listening to complaints by their customers, Atari released an improved version of their previous DOS.

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.

DOS XE supported the double-density and double-sided capabilities of the Atari XF551 drive, as well as its burst I/O.

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.

This DOS supports Turbo 1050, Happy, Speedy, XF551 and US Doubler highspeed drives.

Supports subdirectories and hard drives being capable of handling filesystems sized up to 16 MB.

It has a much lower memory footprint compared to the original 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.

[8] Atari DOS 2.0S, single-sided, single-density disk had 720 sectors divided into 40 tracks.

In 1978, 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.

[21] It is a utility to work with Atari disks and diskettes, based on MyDOS and SpartaDOS.