.D82 File Format

Introduction

A D82 file is a copy of a disk for the Commodore 8250 (and the SFD-1001-class double-sided IEEE-488 drives; the 8250’s format is the one the VICE manual describes). It is the double-sided D80: the same four speed zones repeated on a second side, 154 tracks and 4,166 sectors, with a BAM that grows from two sectors to four.

A standard image is 1,066,496 bytes; with one error byte per sector 1,070,662 bytes (our sum: the manual excerpt we read did not give the error-byte size).

Structure

Side 0 (tracks 1 to 77) is the D80 layout; side 1 (tracks 78 to 154) repeats its zones. The header and the directory are on track 39, the BAM is four sectors on track 38 (sectors 0, 3, 6 and 9) covering 50, 50, 50 and 4 tracks. See Layout, BAM and directory.

Sizes

In the explorer

Drop a .d82 file on the explorer to see the tree (every track and sector, with the header and BAM fields and the directory entries), a picture of the disk, the directory, tables of tracks and sectors, every file to open (a PRG in the .PRG viewer, a SEQ file as text from PETSCII, other files as bytes) and the problems found. The options bar sets the error bytes (detected from the size) and the character set.

Not described

Known, not yet covered

• Reference: REL files (side sectors) are not described and not followed; the SFD-1001 and 8280 are not covered (the 8280 is an X64 device type with no layout here).
• Viewer: graphics characters in names and text are mostly shown as U+FFFD.

Unknown

• Reference: the error-byte size is our sum; the VICE manual’s D82 section is the only source and says nothing of it in the text we read.
• Viewer: no real D82 image is on this Mac and none was found to download, so the reading is checked on built images only, against the track offsets printed in the VICE manual.

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