Questions about the PDP 11/24

From: Pete Turnbull <>
Date: Sun Dec 19 07:18:01 2004

On Dec 19 2004, 12:32, Pierre Gebhardt wrote:

> does anybody know, how much memory the 11/24 can take ?
> I heard something about 1 MB, others say 4 MB somewhere on the web.
Yes, I'm a bit confused...
> Currently, it's configured with 1 MB.

A basic 11/24 processor uses 22-bit addressing but a Unibus uses 18-bit
addressing and therefore can address up to 256KB; the top four bits of
address are therefore dropped by the MMU in a basic 11/24. If it's
fitted with a Unibus Map (KT24, M7134, which also replaces the M9312
bootstrap card) then an 11/24 can use 22-bit addressing, on an extended
Unibus, giving it a 4MB address space. It does this by feeding the
output of the MMU through 31 mapping registers which provide
relocation, so at any given moment you can actually only address 31
pages, each of 4KW (8KB), plus the I/O page; you need to re-program the
mapping registers or the MMU to access the whole 22-bit range.

I don't know where the 1MB limit comes from, that would be a 20-bit
address range.

> Furthermore, does a DELUA - Card properly work in it ?
> There's only the card, the bulkhead assembly is missing, I would have
to build it by myself...

Yes, that should work.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Sun Dec 19 2004 - 07:18:01 GMT

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