Single density: 90 KiB
The Atari 810 records one side of a 5¼-inch disk at single density. Its 40 tracks hold a nominal 90 KiB, some of which is occupied by file system structures and DOS files. Sectors are defined during formatting rather than by additional holes in the disk: this is soft sectoring.
SD is shared with many later drives. A standard 810 cannot read 1050 ED or XF551 DD disks.
SIO addressing and DOS
Two rear sockets connect the 810 to the computer and another SIO device. Switches select the drive number used in names such as D1: and D2:. These numbers identify individual drives; booting normally uses D1:.
The 810 manual specifies at least 16 KB RAM for an Atari 400/800 setup. DOS occupies some computer memory, while the directory and file system structures occupy disk space.