.D80 File Format

Introduction

A D80 file is a copy of a disk for the Commodore 8050, a dual-drive IEEE-488 unit sold with the PET and CBM 8000 series. It uses the same sector model as the D64 (256-byte sectors, linked file chains, 32-byte directory entries) with a larger geometry: 77 tracks of 23 to 29 sectors, 2,083 sectors in all, one side. Its double-sided sibling is the D82.

A standard image is 533,248 bytes. With one error byte per sector it is 535,331 bytes (our sum: the manual excerpt we read did not give the error-byte size).

Structure

Track 39 holds the header (sector 0) and the directory (sectors 1 to 28); the BAM is two sectors on track 38 (sectors 0 and 3). See Layout, BAM and directory.

Sizes

In the explorer

Drop a .d80 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 8050’s DOS 2.5 specifics beyond the header and BAM; the byte-layout of the unused parts of the header sector.
• Viewer: graphics characters in names and text are mostly shown as U+FFFD.

Unknown

• Reference: the size of the error-byte area is our sum (one byte per sector), not a sentence of the manual we read.
• Viewer: no real D80 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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