Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!mips!sjsca4!poffen
From: poffen@sj.ate.slb.com (Russ Poffenberger)
Newsgroups: comp.windows.ms.programmer
Subject: Re: 486SX
Message-ID: <1991May9.200635.9029@sj.ate.slb.com>
Date: 9 May 91 20:06:35 GMT
References: <165722@tiger.oxy.edu>
Reply-To: poffen@SunOS (Russ Poffenberger)
Organization: Schlumberger Technologies, ATE division, San Jose, Ca.
Lines: 44

In article <165722@tiger.oxy.edu> rafetmad@oxy.edu (David Ronald Giller) writes:
>
>> >  > 486SX == 486 w/o "built in" coprocessor
>> >
>> > 486SX == 386 ?
>
>>No, no. The 486 is a complex 64-bit RISC CPU (very similar to the i860) which
>>is microcoded to do 386 instructions. The hardware is totally different.
>
>What?  64-bit?	RISC?  Not last time I looked.	The 80x86 family is about as
>far from the RISC concept as I can conceive.  The 486 is basically just a
>debugged (we hope), optimized version of the 386.  With a debugged (we hope)
>optimized version of the 387 on board.	The fact that the two are in the same
>physical package (on the same wafer) is what gives the 486 its great floating-
>point power and speed.	How could a processor that is coded to emulate another
>possibly ever execute instructions in a single cycly (as the 486 is wont to
>do)?  The 486 is really what the 386 should have been.
>

The 486 employs many of the techniques used in RISC processors to reduce the
number of clock cycles required for an instruction. This is why a 486 runs
roughly twice as fast as as a 386 at the same clock.

>>The 486sx seems to be here for marketing reasons, now that AMD has started
>>shipping their 386 clone CPUs. I think that the 486sx will perform like a 486
>>of equal speed. The question is, since it lacks the internal FPU, if there will
>>be a 487sx. If yes, the 487sx/486sx combination is likely to perform
>>drastically worse than a 486.
>
>If things at Intel haven't changed, shouldn't we expect the 486sx to be a 16-
>bit-bussed version of the 486?	The 8086/8088 and 386/386sx have been this
>route.	A marketing reason indeed, to be able to say 'Almost the same per-
>formance, at a greatly reduced price!!!'.  But for I/O intensive purposes
>(on a 32-bit bus) this is a big mistake.
>
>Indeed, if there were a 486sx/487sx combo, I can't see its marketplace.  Surely
>this combo will be more expensive than a 386/387, and will offer little if any
>performance benefit.  The 386sx really lost a bit of its punch, so much so that
>it paled when compared to a 286 at the same speed (talking in 16-bit mode, now).
>

The 486SX was conceived due to customer pressure. Many board manufacturers
wanted to "gouge" end users by offering ridiculously expensive upgrades
(487SX).