Victor 9000 format
Overview
A very strange format used by the Sirius One / Victor 9000 computer. This machine ran MS-DOS and CP/M, but had a very unusual disc format:
- Variable speed -- 9-zone Z-CLV. The linear velocity of the disc is held fairly constant by rotating certain blocks of tracks slower than others, and storing more data sectors on the outer ("longer") tracks.
- GCR coding -- specifically, a 4-to-5 GCR code which looks like MFM on a timing histogram.
Other than that, they're pretty standard. A DiscFerret can accurately sample and (in theory) decode these discs.
Low level format
GCR code table
From the source code to CW 0.13 by Karsten Scheibler:
| input (hex) | output (bin) | output (hex) |
|---|---|---|
| 0 | 01010 | 0x0a |
| 1 | 01011 | 0x0b |
| 2 | 10010 | 0x12 |
| 3 | 10011 | 0x13 |
| 4 | 01110 | 0x0e |
| 5 | 01111 | 0x0f |
| 6 | 10110 | 0x16 |
| 7 | 10111 | 0x17 |
| 8 | 01001 | 0x09 |
| 9 | 11001 | 0x19 |
| A | 11010 | 0x1a |
| B | 11011 | 0x1b |
| C | 01101 | 0x0d |
| D | 11101 | 0x1d |
| E | 11110 | 0x1e |
| F | 10101 | 0x15 |
