More on building PDP-11s

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed Dec 17 22:51:38 2003

> Yes, well, it's also possible to use Unibus memory on an 11/70, but
> you have to set jumpers on one of the CPU cards. The Unibus memory will
> not be cached, nor will the RH70 Massbus adapters be able to access
> it.

You are limited to 124K words of memory on the Unibus. On the 11/45
that's all the memory the machine can address, and yes, you can have it
all on the Unibus. On the 11/70, that's only a small fraction of the
address space. It seems perverse to have a CPU capable of 22 bit
addressing, and with fast Massbus interfaces, and then cripple it like this!

I suspect you can use Unibus memory on the 11/44 too, with similar
restrictions.

-tony
Received on Wed Dec 17 2003 - 22:51:38 GMT