PDP-11 = Pentium Killer? - test-drb@ccmp.vtda.org

23 Apr 1998

...
 <>fits in the primary cache of an Alpha. If
possible, you'd be using the 
<Alpha
<>essentially as a programmable microengine and programming it to be 
<PDP-11.
<>The reason to fit it in the primary cache is because of how the Alpha 
<boots;

Huh?  a PDP11 emulator for alpha would be written as PAL to get the best 
results.  Caching it is pointless as it's still a 16bit machine and 
would still flog itself to death trying to manage a data file greater 
than fits in ram (4mb max on PDP11 and some of that would be code!). 
You misunderstand. I'm not talking about caching any PDP-11 code or data,
just the Alpha code which executes the emulator. Any memory fetch which
fetches Alpha code is overhead; a real PDP-11 wouldn't have to make that
memory fetch. If you can build a PDP-11 emulator small enough to fit in the
primary cache, all of your memory fetches can be payload.

It wouldn't really be PAL code because it would be executing in the chip's
boot environment; loaded from SROM into primary cache and staying there.
It owuld have a lot of the characteristics of PALcode; the extra registers
which Palcode depends upon would be visible, the MMU would be off, etc., but
it wouldn't really be PALcode because it wouldn't be called by a PAL trap.

Roger Ivie
ivie(a)cc.usu.edu