22 Apr
1998
22 Apr
'98
7:06 p.m.
But, since Alphas must share SOMETHING in common with the PDP-11,
wouldn't it be possible to write a normal program for the Alpha,
running under NT or Linux, that would give PDP emulation at P-II-like
performance? Of course, I'm assuming that some of the PDP instructions
can go unchanged directly into the Alpha. Also, I would guess that a
G3 with an emulator could outperform the slower pentiums. But, then
again, why not emulate a Whirlwind or a Mark I for the same? It would
be much easier. I don't really see how an emulated PDP-11 outper-
forming a pentium would mean anything at all.
Now, making a VAX that would do that is a bit more interesting, though
probably already done. VAX is much more useful these days than PDP-11.
More on this subject: I have long thought that some computers that
are now mostly PD, like the C-64, should be rebuilt in kit form and
sold to kids for $20 each. Now THAT would be nice. Oh, and make them
make their own kernel, and hold a contest for the best one. The
winner gets an emulated PDP-11.
I really must stop eating sugar as well.
incremented value) and three for JSR I Z 10 (fetch 10,
write
incremented
value, stash return address at location pointed to by
incremented
value),
so I could be wrong) each of which depend on the
previous one. You're
not
going to get hot performance out of that unless you
decide that the
main
memory can be built using a 5-port register file on the
chip.
I've occasionally wondered about doing a tight hand-coded PDP-11
emulator that
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;
at reset, it loads its primary cache from an external
serial ROM and
begins
executing it. If you could fit the emulator in the
primary cache, you
could
think of the Alpha+SROM as a PDP-11 microprocessor.
Roger Ivie
ivie(a)cc.usu.edu
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