Victor 9000 format - Revision history

Philpem: /* GCR code table */

2011-03-02T21:19:56Z

‎GCR code table

Philpem at 21:08, 2 March 2011

2011-03-02T21:08:15Z

Philpem: start page, add gcr code table

2011-03-02T20:02:11Z

start page, add gcr code table

New page

[[Category:Disc formats]]

== 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:

{| border="1" style="text-align:center;"
! 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
|}

@@ Line 11: / Line 11: @@
 == Low level format ==
 === GCR code table ===
@@ Line 60: / Line 62: @@
 The eagle-eyed among you might just have noticed that this is the same GCR code table the Commodore 1541 uses... Hardly surprising, seeing as the 1541 is a descendant of the Commodore 8050, which was designed by Chuck Peddle, who also designed the Victor 9000. In a posting to classiccmp on the 2nd of March 2011, Tony Duell (ard p850ug1 demon co uk) says that the disc controller circuitry in the Victor is nearly identical to the circuitry in the 8050. This isn't particularly surprising on the face of it (and really makes the reverse engineering work go quicker!)

@@ Line 16: / Line 16: @@
 From the source code to CW 0.13 by Karsten Scheibler:
 {| border="1" style="text-align:center;"
 ! input (hex) !! output (bin) !! output (hex)
@@ Line 34: / Line 36: @@
 |-
 | 7 || 10111 || 0x17
 |-
 | 8 || 01001 || 0x09
@@ Line 51: / Line 57: @@
 | F || 10101 || 0x15
 |}