17 Mar
2003
17 Mar
'03
12:14 p.m.
On Mar 17, 18:42, Stan Barr wrote:
The Wanderer <quapla(a)xs4all.nl> said:
> A small question, can a Seagate ST-125 be used as a replacement for
a RD5x?
I'd like to know too...
Some info I got on using 3rd-party disks says the following:
"These are the "successes" all done on PDP-11's with the
ZRQCH0 formatter:
.
.
.
(5) Seagate ST-125 (20 MB 3.5" HH): This one is basically a "no
brainer" -- the drive has the same geometry as the RD-31,
and will format as such."
There are basically three ways to get an ST412-like disk to work on an
RQDXx controller.
The easiest is obviously to use a real (or exact equivalent to) RD5x or
RD3x disk, and format it as such.
A second way is to use ZRQCH? in the mode that lets you specify the
type, and format a disk which is slightly bigger (more tracks and/or
more heads), as if it were one of the supported types. That only works
for an RQDX3 with late(ish) ROMs.
A variation on this for an RQDX1 is to use really old ROMs and a disk
that behaves sufficiently like an RD51 or RD52 (eg has the right number
of cylinders). Not all disks work, and they may stop working if you
substitute later ROMs (real RD51/52 disks are OK, the firware
recognises them and updates the format). The reason is that the
firmware in the RQDX1/2 recognises disk geometries by probing, by
playing tricks with the disks. The earliest version of the firmware
had only very simple tests, and could be fooled (I used to use a Rodime
3.5" drive on my RQDX1), but later firware has more tests (and six or
eight disk types) and if it doesn't recognise the disk, it won't play.
I once exchanged some email with the guy at DEC who wrote those
routines so I have some what they do, but no details.
The third method is to use ZRQCH? or ZRQCG? in the mode that asks all
the relevant questions about geometry and disk type. This only works
for RQDX3s, but if you can work out what all the RCTs, ZBNs and other
TLAs mean, and know how to work out all the numbers required, you can
format anything and call it RDanything. And later versions of DEC OSs
will be perfectly happy. The problem is knowing how to work out the
answers. I did it once, and Tim Shoppa (IIRC) has also done it, but as
far as I know, the full information isn't published anywhere. If you
want to try this, I can look out my notes about the TLAs and how to
work out the type numbers, and look up the manuals to see how to get
ZRQC?? into the right mode (I recall that different versions were
slighly different, if you see what I mean).
--
Pete Peter Turnbull
Network Manager
University of York