Hardware / Peripherals / Atari XF551

HARDWARE / FLOPPY DISK DRIVES

Atari XF551

A double-sided 5¼-inch drive with a nominal DD capacity of 360 KiB. Full capacity requires a suitable DOS, such as DOS XE; the initially bundled DOS 2.5 supports only smaller formats.

Two heads and 360 KiB

The XF551 uses both disk sides without turning the disk over. Its full double-sided DD format holds 368,640 bytes, or 360 KiB, before file system overhead. This differs from two independent sides of a manually flipped disk.

The drive also supports SD and ED. Unusual loaders and protection on older disks may, however, depend on earlier drives' behaviour.

DOS and full disk capacity

The initially bundled DOS 2.5 cannot use the full double-sided DD format. Writing 360 KiB requires a suitable system, such as DOS XE. The drive also supports Percom configuration and faster SIO commands. High-speed transfers require a DOS or loader using those commands; older software uses standard transfers.

Interface and compatibility with older drives

Two SIO sockets allow another device to be connected, and rear switches select the drive number. BUSY lights during disk access.

Reading flipped disks and detecting density may behave differently depending on electronics, drive firmware and mechanism.

Sources and further reading