Not a DOS disk
Commodore Amiga
Severity: ModerateWhat Does This Error Mean?
Not a DOS disk means the Amiga cannot recognise the filesystem on the inserted floppy. The disk may be unformatted, formatted for a different computer (PC, Atari ST), or physically damaged.
Affected Models
- Commodore Amiga 500
- Commodore Amiga 500+
- Commodore Amiga 600
- Commodore Amiga 1200
- WinUAE emulator
Common Causes
- Disk is unformatted — a brand new blank disk straight from the box
- Disk formatted for MS-DOS or Atari ST — AmigaOS cannot read these natively
- Disk physically damaged or demagnetised — the boot block is unreadable
- Disk is a copy-protected game disk — the intentionally non-standard format confuses the OS
- Wrong disk type inserted — DD disk in a HD drive without a cover sticker
How to Fix It
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If the disk is blank: format it using Workbench — Icons menu > Format Disk.
Insert the blank disk, wait for its icon to appear (it may show as Not Validated first), then go to Icons > Format Disk. Give it a name and click Format. This creates an AmigaOS filesystem on the disk.
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If the disk came from a PC: you need CrossDOS or a similar tool to read it.
AmigaOS 2.1 and later include CrossDOS for reading MS-DOS formatted disks. Earlier versions require a third-party utility. Note that copy-protected PC software disks may still be unreadable.
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If it is a copy-protected game: load it with the game loader, not from Workbench.
Many commercial Amiga games use non-standard disk formats to prevent copying. These disks deliberately appear as Not a DOS disk from Workbench — boot the game directly by restarting with the disk in DF0.
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On WinUAE: check the disk image format — ADF works for standard disks, IPF for copy-protected titles.
Standard game and software disks use .adf format. Copy-protected originals require .ipf format and the CAPS/SPS plugin for WinUAE.
Frequently Asked Questions
Can the Amiga read PC floppy disks at all?
Yes, with CrossDOS (included in AmigaOS 2.1+) the Amiga can read and write MS-DOS formatted disks. However, the two systems used different physical formats: Amiga disks are 880KB, PC HD disks are 1.44MB.
Why do copy-protected game disks show as Not a DOS disk?
Game publishers deliberately wrote the boot block in a non-standard format to frustrate disk copiers. The Amiga could still boot the disk directly, but copying software could not replicate the format — protecting the game.