[TUHS] Booting PDP-11's from RX02's

[TUHS] Booting PDP-11's from RX02's

[Noel Chiappa]

    > From: Don North <north at alum.mit.edu>

    > .. the hardware bootstrap reads track 1 sectors 1, 3, 5, 7

Ah, thanks for that. Starting to look at the code, I had missed the
interleave.

So does DEC do anything with track 0, or is it always just empty?

	Noel

[TUHS] Booting PDP-11's from RX02's

[Noel Chiappa]

    > From: Don North

    > Track 0 is not used by standard DEC software

I wonder why DEC did't use track 0. The thing is small enough (256KB in the
original single-density) that even 1% is a good chunk to throw away. Does
anyone know? (I had a look online, but couldn't turn anything up.)

If I had to _guess_, one possibility would be that track 0 is the innermost
track, where the media is moving the slowest, and as a result it's more
error-prone. Another is that IBM used track 0 for something special, and DEC
tried to conform with that. But those are pure guesses, I would love to know
for sure.

	Noel

[TUHS] Booting PDP-11's from RX02's

[Ron Natalie]

I think just like everything else the boot rom just pulls in the first
sector of the disk.   I had RX02s on many of the BRL Gateways (my
implementation that replaced your MIT Gateway while you were in exile).
We put a V6 file system and I must have had a regular V6 boot block on it
with a RX02.   There might be someone still at BRL who might remember where
this stuff is.   I certainly don't have it.

BRL PDP-11 kernels had both V6 and V7 file systems in them but I'd have to
believe I was booting off a V6 one.

[TUHS] Booting PDP-11's from RX02's

[Noel Chiappa]

So, I'm winding up to boot Unix V6 from an RX02 floppy. So I need two things:

- Details of how DEC ROM bootstraps boot from RX02's. I vaguely recall seeing
documentation of this somewhere (e.g. which sectors it loads, etc), but now I
can't find it. Don North has dumps of the RX02 ROM's, but I'm too lazy to read
through the code and figure out how they work. Is there some documentation
which covers it? I did a quick Google search, but if there is anything out
there, my Google-fu was inadequate.

- Did anyone ever do an RX02 driver for the V6 disk bootstrap? (Well, I guess
a V7 driver would work, too.) Note: what I need is _not_ either i) the Unix OS
driver for the RX02 (I found one of those already), or ii) a driver for the v7
standalone second-stage bootstrap (which would probably be in C). The thing
I'm looking for would be called rx.s, or something like that. Yes, I could
write it, but again, I'm lazy! :-)

      Noel