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_at_cc.usu.edu
>
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Received on Wed Apr 22 1998 - 18:06:19 BST