17 Mar
2015
17 Mar
'15
12:51 p.m.
On Mar 17, 2015, at 3:46 PM, Brent Hilpert <hilpert
at cs.ubc.ca> wrote:
On 2015-Mar-17, at 12:27 PM, Paul Koning wrote:
True, though I think in practice PDP-11s came with boot ROMs. Even fairly early 11/20s
did ? the M792 discrete diode array, programmed with diagonal cutters :-).
paul
...
MRAM is non-volatile, sure. I?m not sure its write limit is high enough to be used as a
substitute for main memory. In any case, what PDP-11 operating systems use the
non-volatility of memory? I know of one: RSTS-11. But RSTS/E dropped that (it reboots on
powerup instead). That makes sense, given that semiconductor memory appeared fairly early
in the PDP-11 product life, and none of that came with battery backup. In other words,
only some of the models in some configurations offered non-volatile memory, which made it
fairly uninteresting for operating systems to support.
Well, even if the OSs didn't support restart, non-volatility of core was useful for
retention of the bootstrap program on the front-panel/pre-boot-ROM machines, just so you
didn't have to re-toggle the bootstrap at every power-up.