Qbus split I&D?

Christian Gauger-Cosgrove captainkirk359 at gmail.com
Tue Mar 17 14:03:30 CDT 2015

On 16 March 2015 at 23:42, Eric Smith <spacewar at gmail.com> wrote:
> Not including parity or ECC, it takes two devices to fill the entire
> 4MB address space of the PDP-11/70. Either parity or ECC will require
> another one additional device, which won't be fully utilized.
> Ordinary SRAM is cheaper, but $110.16 for enough RAM chips to max out
> a PDP-11/70 doesn't seem all that expensive, unless you're comparing
> to DDR SDRAM DIMMs for PCs.
True, SRAM would be cheaper, and you can find faster SRAM and DRAM
than the currently available MRAM (if I recall correctly). But then
you lose the benefits of MRAM in the first place: It's non-volatile,
like core memory, and doesn't need battery backup (as you'd need if
you wanted to make SRAM "non-volatile"). Plus since they're modern
devices, they would be a massive upgrade to the PDP-11/70s performance
in place of its normal MOS memory or core memory. (Whether it would be
an improvement on the speed of the PEP70, I do not know.)

Christian M. Gauger-Cosgrove
Contact information available upon request.

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