ATR

File Format
Name	ATR
Ontology	Electronic File Formats Disk Image Formats ATR
Extension(s)	.atr

ATR is an Atari floppy disk image format associated with SIO2PC, a product that connects Atari and PC computers. It was created by Nick Kennedy and is supported by most Atari emulators.

Format

Files have a 16-byte header, followed by a raw sector-by-sector dump of the disk.

Header Structure

There is a 16 byte header with the following information (WORDs are in [1]little endian format):

Identification <WORD>: ($9602). This word is the 16 bit sum of the individual ASCII values of the string of bytes: "NICKATARI".

Size of disk image <WORD>: The size is expressed in "paragraphs". A paragraph is sixteen bytes, thus Size = Image size in bytes / 16.

Sector size <WORD>: 128 ($80) or 256 ($100) bytes per sector. Note that the original documentation only specifies two sector sizes, in practice however there is also sector size 512 ($200). 512 byte sectors were introduced by SpartaDOS X, and are sometimes used to create large ATR images. Some Atari Emulators and Peripheral emulators such as Altirra and AspeQt can make use of the 512 byte sectors in ATR files.

See also

• Atari 810 (physical disk format)
• Atari File Management Subsystem (filesystem)

Specifications

• ATR File Format Description

Software

• Atari-FileManagement (Old windows binary. Still works on Windows 7, but only barely.)
• Adir (Untested MS-DOS binary & source code.)
• SIO2PC

Sample files

• http://www.page6.org/pd_lib/pd_lib.php
• http://www.mushca.com/f/atari/
• ftp://ftp.pigwa.net/stuff/collections/Homesoft/