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From: basker@diku.dk (Tom Thuneby)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: 486SX - Intel now telling lies
Message-ID: <1991May31.210116.16012@odin.diku.dk>
Date: 31 May 91 21:01:16 GMT
References: <1991May29.191233.18863@cunixf.cc.columbia.edu> <1991May29.212337.7684@thyme.jpl.nasa.gov> <1991May29.230433.10095@maverick.ksu.ksu.edu> <1991May30.164751.16585@thyme.jpl.nasa.gov> <1991May31.034938.21083@maverick.ksu.ksu.edu>
Sender: basker@freja.diku.dk
Organization: Department of Computer Science, U of Copenhagen
Lines: 41


A lot of people seem to disagree about Intels reasons behind making
the 486. I'd like to throw in my 'two cents' worth.

Several people have pointed the following things out (I don't know
if they're all facts; but it sounds OK to me):

1) The yield of a batch of 25 MHz 486's is around 14%
2) More than half of the silicon is used by the coprocessor
3) The coprocessor has a relatively high probability of errors
4) Some of the chips that fail a 25 Mhz test will not fail 20 Mhz
5) The coprocessor is disabled by removing its connection with the
   rest of the chip. Once the chip has been made, it is impossible
   to disable/reenable these connections.

From these informations, the following picture appears:

The yield of the 486sx is far better than that of the 486. A wild
guess on my part is, that the percentage of failed chips is
decreased by 1/3. This means a yield of 43% for the 486sx. Compare
that to the 14% of the 486.

The 486sx is NOT a 486 that has failed its coprocessor test. It's a
486 with a disabled coprocessor, that has only been tested for 20
MHz. It is utterly impossible (with the technology of today) to
re-enable the coprocessor, even if it would have functioned
perfectly.

End of reasoning, my own thoughts follow.

I suspect, that the pin incompatibility (and thus the need for a
487) is a marketing issue. When comparing the cost of the 486sx to
the cost of the 386-33, one should also consider the cost of
external cache, memory, and the like. A 33 Mhz motherboard (without
processor) costs somewhat more than a 20 Mhz motherboard. Thus, the
total cost of the computer might be less for a 486sx-based system.

Constructive criticism appreciated. I apologize for errors in
spelling and grammer; English is not my native tongue.

			Tom Thuneby (basker@diku.dk)