Xref: utzoo comp.misc:2449 comp.arch:4920
Newsgroups: comp.misc,comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Japanese 32-bit micro can be a 68020 or 80386
Message-ID: <1988May22.023131.17892@utzoo.uucp>
Organization: U of Toronto Zoology
References: <2006@sugar.UUCP>
Date: Sun, 22 May 88 02:31:31 GMT

Let's see, what's a microprogrammable machine?  Well, it uses a simple
and often rather bizarre instruction set, running one instruction per
cycle, to interpret a different instruction set.  Now, name three important
differences between that and something like a Mips machine, except that
the Mips machine can run programs in "native" mode too.  The original
Stanford MIPS project looked a whole lot like a microengine running
microcode out of main memory, and I seem to recall seeing it explicitly
explained in those terms.  The MipsCo machine looks rather less like a
microengine, mind you.  (I'd imagine there are good reasons for the change,
since MipsCo doesn't seem to choose the color of the box without systematic
evaluation of the alternatives... :-))

You can make some gains by specializing the hardware for emulating other
machines.  On the other hand, running the programs "native" is usually
faster, so why bother?  Microprogramming looks, right now, like an idea
whose time has come AND GONE.