PDP-11 addressing question and a model round-up

[Eric Smith]

Pete Turnbull wrote:
> However, early versions of
> the KDF11-A had 18-bit ODT while later versions, and all KDF11-Bs, had
> 22-bit ODT.  All would still happily cope with 22-bit memory under
> control of the MMU (as far as I remember -- someone please correct me
> if I'm mistaken), providing they are in a 22-bit backplane.

Are you sure that there was a difference in the ODT?  I thought the
ODT was the same in all F11 chipsets, and the difference was purely
a matter of whether the KTF11 MMU was installed, and whether the module
wired the top four address lines to the bus.

Hmmm... makes me wonder whether ODT on a system without the MMU installed
can access physical memory above the 28KW mark.  I may have to try that.

Eric