17 Jul
2023
17 Jul
'23
9:48 a.m.
On Mon, Jul 17, 2023 at 12:28 PM Henry Bent via cctalk
<cctalk(a)classiccmp.org> wrote:
I just noticed that images of a full RX50 floppy set
for Ultrix-32m 1.2 was
posted on Bitsavers (
http://bitsavers.trailing-edge.com/bits/DEC/vax/ultrix/1.2/ULTRIX-32M_V1.2_…
). I am having difficulty parsing these images into a usable raw format
for SIMH.
You are not the first to encounter this.
Oddly though, in the "raw" dump the
bootloader doesn't
start until 0x1400, and a number of the other disks I looked at appear to
have odd holes/zeroes in them. IMD format dumps of the 1.2 disks are
provided but when I converted the IMD format to a raw image I got the same
issue.
Yes. IMD->raw just decompresses the IMD format back into the exact
number of bytes, in the same order, of the original media. Keep
reading for why this is not sufficient...
I'm almost thoroughly unfamiliar with IMD - is
there some obvious
extraction/conversion option that I am missing here? Were these disks
actually imaged correctly? I would appreciate any suggestions.
This is not an IMD issue. IMD files are numbered as they come off the
media and can be written back out, as is, to make physical media,
which was the primary purpose. For nearly all cases, this also
happens to match sequential sector order so that the same data can be
used for emulators (simh and others). The one case where the two
situations don't match is the RX50.
What DEC did was to put a software-defined sector interleave and track
shifting into their RX50 controllers (RQDX1 et al). In addition to
the sectors on the disk not being in "logical filesystem order", track
0 gets moved to the end of the list
From: http://www.chdickman.com/pdp11/pro380.txt
"The RX50 floppy starts at track 1. Track 0 is logically placed after
track 79. The sectors are interleaved 1, 3, 5, 7, 9, 0, 2, 4, 6, 8,
10. The track shift and interleave must be taken into account when
moving disks between real PDP-11 and emulators."