PDP-11 = Pentium Killer?

From: Captain Napalm <spc_at_armigeron.com>
Date: Wed Apr 22 18:16:54 1998

It was thus said that the Great Daniel A. Seagraves once stated:
>
> What would happen if we made a PC-sized PDP-11 processor using the Alpha
> technology? (On a single chip, clock it at ~300-400 MHz)

  It would be interesting. The smaller instruction set would mean you have
enough silicone left over to implement internal cache, increasing
performance, and it would probably be bug free (or nearly so) since the
architecture is old enough to have most of the bugs worked out (I would
guess).

  But I'm not sure what word size the PDP-11 was. If it's 16 bit then most
modern software probably wouldn't port that well to it, and if the word size
isn't a multiple of 8, then interfacing memory might be a bit of a problem.

  Then again, I'm a software guy anyway ...

> As the PDP-11 instruction set is MUCH better than 80x86, would it outrun
> a PC? Could this be a Pentium Killer?

  There are plenty of architectures out there with a much better instruction
set than the 80x86 (oh, the 68k, VAX, ARM, MIPS, PPC and Alpha come to mind)
but the 80x86 is still in use for two reasons: existing code base and it's
rare for programing to be written in assembly anymore (I'm talking about
mainstream stuff). Typically, there are four ways to improve speed in
software: better algorithms (which are independant of language used to
implement them generally and usually give the best improvement), inline
commonly used routines (for this to work, they typically have to be small
and used very frequently - I was able to cut the runtime in half of some C
code by doing this), faster hardware (and you can be pretty sure that
computers twice as fast as the current ones will be out within a year, two
tops) or the critical portions in assembly (usually one one or two routines,
never more than half a dozen in my experience. Doom was done this way - all
in C except for two routines).

  In three of the cases, this requires finding the routines that are
executed most often, or consume the most time and adjusting those routines,
although the easist thing is the one case not covered by this - new
hardware.

  -spc (Writing portable code is tricky ... )
Received on Wed Apr 22 1998 - 18:16:54 BST