1224kB 5.25” DSDD GCR

The Victor 9000 / Sirius One was a rather strange old 8086-based machine which used a disk format very reminiscent of the Commodore format; not a coincidence, as Chuck Peddle designed them both. They’re 80-track, 512-byte sector GCR disks, with a variable-speed drive and a varying number of sectors per track — from 19 to 12. Disks can be double-sided, meaning that they can store 1224kB per disk, which was almost unheard of back then. Because the way that the tracks on head 1 are offset from head 0 (this happens with all disks), the speed zone allocation on head 1 differs from head 0…

Zone Head 0 tracks Head 1 tracks Sectors Original period (ms)
0 0-3   19 237.9
1 4-15 0-7 18 224.5
2 16-26 8-18 17 212.2
3 27-37 19-29 16 199.9
4 38-47* 30-39* 15 187.6
5 48-59 40-51 14 175.3
6 60-70 52-62 13 163.0
7 71-79 63-74 12 149.6
8   75-79 11 144.0

(The Original Period column is the original rotation rate. When used in FluxEngine, the disk always spins at 360 rpm, which corresponds to a rotational period of 166 ms.)

*The Victor 9000 Hardware Reference Manual has a bug in the documentation and lists Zone 4 as ending with track 48 on head 0 and track 40 on head 1. The above table matches observed data on various disks and the assembly code in the boot loader, which ends Zone 4 with track 47 on head 0 and track 39 on Head 1.

FluxEngine can read and write both the single-sided and double-sided variants.

Options

  • Format variants:
    • 612: 612kB 80-track DSHD GCR
    • 1224: 1224kB 80-track DSHD GCR

Examples

To read:

  • fluxengine read victor9k --612 -s drive:0 -o victor9k.img
  • fluxengine read victor9k --1224 -s drive:0 -o victor9k.img

To write:

  • fluxengine write victor9k --612 -d drive:0 -i victor9k.img
  • fluxengine write victor9k --1224 -d drive:0 -i victor9k.img

References

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