Disk format for the C64 1541 disk drive

The 1541 disk drive used 5.25" disks. The standard CBM DOS format is 170 KB with 35 tracks and 256-byte sectors providing 165K for storage.

Although standard disks are only 35 tracks, it was mechanically possible to get 40 tracks by using either custom formatting or third party DOS's.

The format described in this section also applies to .D64 disk images that can be used with both Emulators like VICE and the PI1541 attached to a real C64.

Physical layout

Physical Disk Layout for the 1540/1541

Directory Track

Directory track 18

Block Availability Map

Directory track 18 sector 0, the BAM and disk details

File format

How files are stored on the disk

D64 Image Format

CBM DOS as a single image for Emulators

Auto boot

Making a disk bootable on the C128

GEOS Extensions

GEOS VLIR (Variable Length Index Record)