Disk Error
Atari Atari ST
Severity: ModerateWhat Does This Error Mean?
An Atari ST disk error means TOS could not read from or write to the floppy disk. The most common causes are a dirty drive head, a worn disk, or inserting a 3.5-inch HD disk (1.44MB) without covering the HD hole to make it look like a DD disk.
Affected Models
- Atari ST
- Atari STF
- Atari STE
- Atari Mega ST
- Steem emulator
- Hatari emulator
Common Causes
- Drive head dirty from years of use
- Disk physically worn, demagnetised, or damaged
- 3.5-inch HD disk used without covering the high-density hole — the ST drive reads it incorrectly
- Disk formatted on a PC at 1.44MB — the ST only reads 720KB DD format natively
- Drive head misaligned after heavy use
How to Fix It
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Use a floppy drive head cleaning disk.
A dirty head is the most common cause of persistent disk errors on 30+ year old drives. Insert a cleaning disk (dry or lightly moistened) and run it for 30 seconds. Try the disk again.
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If using 3.5-inch HD disks, cover the HD hole with tape.
HD disks have two holes — one for the write-protect tab and one at the opposite corner that signals the drive to use HD mode. The Atari ST drive cannot handle HD mode. Cover the second hole with a small piece of opaque tape to make it behave as a DD disk.
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Try the disk in another Atari ST or drive to confirm whether the fault is the disk or the drive.
If the same disk works in another drive, the problem is the drive (dirty or misaligned head). If it fails in multiple drives, the disk itself is damaged.
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On Hatari or Steem: re-attach the disk image and verify the file is a valid .ST or .MSA image.
Corrupt .ST or .MSA files produce disk errors in emulation. Download a fresh copy of the image from a verified source.
Frequently Asked Questions
What disk format does the Atari ST use natively?
The Atari ST uses 3.5-inch double-density (DD) disks formatted to 720KB in two-sided format. Single-sided disks hold 360KB. The ST cannot natively format or read 1.44MB HD disks without third-party software.
Can the Atari ST read PC-formatted disks?
Yes, but with caveats. PC 720KB disks formatted as MS-DOS can be read with third-party software like PC-Ditto or DC-Squish. Pure TOS cannot read MS-DOS disks natively.