SCSI options for PDP 11/23 - test-drb@ccmp.vtda.org

27 Feb 2002

On Feb 27, 20:49, Zane H. Healy wrote:

...
  OK, what I see that concerns me is the fact you're
using a 11/03 box.
 Unless I'm mistaken the 11/03 was only Q16, which has me wondering how
 you're even running a 11/23 CPU, which should be Q18, in it (it's possible
...
  someone upgraded the backplane to be 18-bit). 
An 11/03 backplane is already 18-bit.  BDAL16 and BDAL17 are bussed so it
can use parity memory.

It's also easy to upgrade to 22-bit, by soldering wrirewrap wire onto the
extra 4 lines, though any 11/23 or 11/23+ will work fine (as an 18-bit
system) without doing that.  I can't think of anything that will fail to
work on such a system, apart from software that needs more than 124KW of
memory, obviously.  Specifically, I/O page access will work coreectly for
any properly designed device, and RT-11, RSX-11, etc will just see it as a
normal 18-bit system.

Oh, and an 11/23 would work fine on a 16-bit backplane, unless you wanted
to use parity memory.  The MMU wouldn't be useful (you could take it out,
though you don't have to; an 11/23 will work fine with 28KW and no MMU
chip).

-- 
Pete						Peter Turnbull
						Network Manager
						University of York