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From: torvalds@cc.helsinki.fi
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Comparing 486 to 386 Systems
Message-ID: <1991Apr6.191106.5863@cc.helsinki.fi>
Date: 6 Apr 91 19:11:06 GMT
References: <40409@netnews.upenn.edu> <1991Apr4.062503.1325@agate.berkeley.edu>  <27865@neptune.inf.ethz.ch>
Organization: University of Helsinki
Lines: 39

In article <27865@neptune.inf.ethz.ch>, brandis@inf.ethz.ch (Marc Brandis) writes:
> In article <1991Apr4.204923.29300@agate.berkeley.edu> c60b-1eq@web-1c.berkeley.edu (Noam Mendelson) writes:
>>Most people also subscribe to the notion that if the number is higher it's
>>necessarily much more powerful, where in fact:
>>		(486 - 386) < (286 - 86) << (386 - 286).
> 
> Well, I guess you subscribe to a similar notion which is also wrong, like most
> performance comparisons that oversimplify. In fact, (386-286) is the smallest
> of the differences, not by far the largest as your relation indicates. Give
> me any instruction on the 386 except multiplies that are faster than on the 
> 286. I know you will not find one. Of course, I am comparing apples to apples
> and oranges to oranges, namely CPUs running in the same mode at the same clock
> frequency.

I don't think speed was the primary difference meant here between the
286 vs the 386. The main point is that "featurewise" the gap between the
286 and 386 is much larger than between the 386 and 486. Quite frankly
the x86 family before the 386 is brain-dead (I just LOVE to be flamed :-),
while the differences between the 386/486 are mostly cosmetic.
  Yes - the 486 has an in-built FPU, and some cache. Both these things
are easy to add later to a 386, and while not as fast, it becomes
functionally about 99% eqvivalent. But why do you think there are a LOT
of programs that simply won't work on a 286 or less? (windows "kind of"
works on these, but most u*ix etc want a 386 at least).
  Fos a machine running just dos, the only NOTABLE difference between
ANY x86 is speed, so there you could use a 8088 at 500MHz if they made
them. For anything else (read unix, windows, etc) you want a 386 or a
486 (yes I'm oversimplifying). The 286 just won't cut it.

> 
> While it is true that the 486 is not that much faster than the 386 on non-fp
> code running 16-bit software, you should see a larger difference running 
> 32-bit code.
>

Yes - the 486 is faster, but that's about it. It has a few new commands,
most of which are cache-controlling commands, and as such "never" used.

		Linus "God, not the flamethrower .. ahhhh" Torvalds