17 Jul
2023
17 Jul
'23
9:38 p.m.
On Mon, Jul 17, 2023, 3:34 PM Chuck Guzis via cctalk <cctalk(a)classiccmp.org>
wrote:
On 7/17/23 11:53, Ethan Dicks via cctalk wrote:
Yup. The Rainbow's track 0 and 1 were not interleaved to make the boot
loader easier... I think the decmate did yhe same but with different
tracks...
The rainbow also had a cool partitioning format that looked like it was
some general thing, but I never saw it elsewhere or have found an
electronic copy of the printed docs I pulled off dec's tops20 support
machine from the LSG in the late 80s
Warner
--Chuck
Chuck Dickman's algorithm is in lbn2rx50.c
#define RX50_TRACKS 80
#define RX50_SECTORS 10
int interleave[] = { 0, 2, 4, 6, 8, 1, 3, 5, 7, 9 };
track = lbn/RX50_SECTORS;
track = (track + 1)%RX50_TRACKS;
sector = lbn%RX50_SECTORS;
sector = (interleave[sector] + 2*(track - 1) +
RX50_SECTORS)%RX50_SECTORS;
Depends on the application. Files-11 RX50 encoding is a bit stranger,
with Track 79 mapped to physical track 0.
I can pass my algorithm along, if anyone is interested.
On the other hand, DECMate II and Rainbow use sector interleave but not
track skew.
If anything can be said about DEC, they were consistent in their
inconsistency.