Atari DOS - Disk Formats

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 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 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. 88K capacity.
• Single-Sided, Double-Density: 40 tracks with 18 sectors per track, 256 bytes per sector. 180K capacity. Readable by the XF551 and the 815.
• Single-Sided, Enhanced-Density: 40 tracks with 26 sectors per track, 128 bytes per sector. 127K capacity. Readable by the 1050 and the XF551.
• Double-Sided, Double-Density: 80 tracks (40 tracks per side) with 18 sectors per track, 256 bytes per sector. 360K capacity. Readable by the XF551 only.