Intel 486SX fpu?

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PATRICK J LARKIN

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Dec 7, 1994, 11:51:50 AM12/7/94
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Is there any such thing as a math coprocessor for an i486sx25? I can't seem
to get a straight answer. Some tell me you need the sx2 overdrive, some tell
me it doesn't exist.

Could someone that does know let me know. I need to get some life from this
machine for a while yet.

Thanx.

-P.L.

Patrick J. Larkin Penn State '90
User Consultant Penn State 1994 Big 10 Champs
Lehigh University @-->-->--1995 Rose Bowl
---------------------------------------------------------------
WWW--> http://www.lehigh.edu/pjl2/public/www-data/pjl2.html
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x93...@wmich.edu

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Dec 7, 1994, 2:11:51 PM12/7/94
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You can get i487sx math coprocessor from your favorite computer store. That
simple. I just plug on to you coprocessor socket and runs almost same as
i486DX. Price about $70 (Intel) and dropping.

Seung Yup Oh

PATRICK J LARKIN

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Dec 8, 1994, 9:31:31 AM12/8/94
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In article <3c4p76$3a...@ns2.CC.Lehigh.EDU>, pj...@ns2.CC.Lehigh.EDU (PATRICK J LA
RKIN) writes:
>
>Is there any such thing as a math coprocessor for an i486sx25? I can't seem
>to get a straight answer. Some tell me you need the sx2 overdrive, some tell
>me it doesn't exist.
>
>Could someone that does know let me know. I need to get some life from this
>machine for a while yet.
>
>Thanx.
>
>-P.L.
>
>Patrick J. Larkin Penn State '90
>User Consultant Penn State 1994 Big 10 Champs
>Lehigh University @-->-->--1995 Rose Bowl
>---------------------------------------------------------------
> WWW--> http://www.lehigh.edu/pjl2/public/www-data/pjl2.html
>---------------------------------------------------------------
>
Well, as always, I've gotten no definite answer! The mail I received was
split. Some people said "buy the i487sx" and some say "there is no math
coprocessor for 486sx."

I looked up an i487 and can't find it on my Intel price list.
Does anyone know UNEQUIVOCALLY the answer to this question. Please help if
you can.

David T Hollis

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Dec 13, 1994, 9:10:17 AM12/13/94
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PATRICK J LARKIN (pj...@ns2.CC.Lehigh.EDU) wrote:
: In article <3c4p76$3a...@ns2.CC.Lehigh.EDU>, pj...@ns2.CC.Lehigh.EDU (PATRICK J LA

You will need an OverDrive chip. You should find that in any Intel
catalog/price list. Actually, you probably already have a math-co, it's
just defective so it has been disabled. All the OverDrive chip will
really do is disable your current processor and become the new CPU (with
a working fpu). You should be able to get an OverDrive at any local
computer store (CompUSA, or Computer City or any equivalent)..

Sivasankar Chander

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Dec 14, 1994, 3:25:29 PM12/14/94
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PATRICK J LARKIN (pj...@ns2.CC.Lehigh.EDU) wrote:
: Well, as always, I've gotten no definite answer! The mail I received was

: split. Some people said "buy the i487sx" and some say "there is no math
: coprocessor for 486sx."

: I looked up an i487 and can't find it on my Intel price list.

There is (or was) an i487sx. Internally it's identical to a 486DX, but the
pinout is different. I think NMI# and a few other signals have been bonded
to different pins, so you can't replace it with a 486DX (unless you have one
of those special adapter boards that some enterprising guy cooked up).

Incidentally, the guy who allegedly came up with this pinout trick for the
487sx was apparently Vinod Dham, who is one of the "spin doctors" in the
present Pentium FDIV cover-up.

Sivasankar Chander
"I speak for myself, not for my employer(s)"

Ron Newman

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Dec 16, 1994, 12:57:17 PM12/16/94
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In article <bent.60....@engr.latech.edu>,
Ben Tarver <be...@engr.latech.edu> wrote:
>So they differentiate
>all newly produced 80486s as being 80486DX (better, faster,with FPU) or
>80486SX (lesser,slower,without FPU). The ONLY difference between the two chips
>was the speed of math operations - with the 486SX doing all it's math in
>software.

Somehow, I don't think that's what you meant to say. (How could a
chip do math in software?)
--
Ron Newman MIT Media Laboratory
rne...@media.mit.edu

Ben Tarver

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Dec 14, 1994, 3:05:59 AM12/14/94
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>Well, as always, I've gotten no definite answer! The mail I received was
>split. Some people said "buy the i487sx" and some say "there is no math
>coprocessor for 486sx."

>I looked up an i487 and can't find it on my Intel price list.
>Does anyone know UNEQUIVOCALLY the answer to this question. Please help if
>you can.

>Patrick J. Larkin Penn State '90
>User Consultant Penn State 1994 Big 10 Champs
>Lehigh University @-->-->--1995 Rose Bowl
>---------------------------------------------------------------
> WWW--> http://www.lehigh.edu/pjl2/public/www-data/pjl2.html
>---------------------------------------------------------------

Ok, the story goes something like this:

Around '89 - '90 or so Intel released the 80486. There was no SX or DX suffix.
The chip ran at 25 and 33Mhz, And the only way you could get a 486 was with a
WITH a FPU. Then, a year or so later the marketing boys at Intel deside there
is an unfilled market nitche between the 386 and 486, so they come up with the
bright idea of selling a 486 without the FPU. Problem is the newer FPU-less
die will take a while to ramp up, so Intel takes an existing 486 die and
'disables' the FPU (whether the 486 FPU was simply defective, or they shorted
out the FPU, or disabled it with a laser, I don't know). So Intel now has 2
486 cpus - one with a functional FPU, one without.

To backup a bit, the DX and SX suffixes were origionally created when Intel
started making a 16 386 (the 386 origionally didn't have a suffix, either).
They dubbed the 16 bit 386 the 386sx (for single width data path) and the 32
bit 386 the 386dx (for double width data path). Sounds sensable, right?

So here Intel has two different 486 cpus. They deside (in their infinite
wisdom :) that the computer market is already familiar with the SX/DX on the
386 (with the 386SX being the lesser, slower chip). So they differentiate

all newly produced 80486s as being 80486DX (better, faster,with FPU) or
80486SX (lesser,slower,without FPU). The ONLY difference between the two chips
was the speed of math operations - with the 486SX doing all it's math in
software.

So the thing to do, if you wanted to upgrade from a 486SX, was buy a 486DX (of
the same speed) and drop it in, right? NOOOOOOOOOOOOO!!!!!!!
Intel (In Their INFINITE Wisdom :) changed the pinout (I think) on the
486SX, so you couldn't just replace it with a 486DX. So what were owners of
486SX machines to do?? Well, son, thats where the fabeled Overdrive (tm Intel)
socket came in!! Into that socket went the NEW INTEL 80487SX cpu!! What was
the 487SX, you ask?

The 80487SX was essentially a 80486DX with an extra pin that, when inserted
into the Overdrive (tm Intel) socket, would COMPLETELY DISABLE the 486SX on
the motherboard. So, in a 487SX upgraded computer you would have your 486DX
(labeled 486SX with a different pinout, and the FPU disabled - costing Intel
as much to make as a normal 486DX, if not more) sitting, doing nothing,
completely disabled, and your new 486DX chip (labeled 487SX, with an extra
pin to disable the other 486) sitting in your Overdrive (tm Intel) socket,
effectively giving you the power of a 486DX! Wow! Impressive, huh?

I think the whole concept was for Intel to force people to buy two cpus from
Intel. You couldn't just yank your now-useless 486SX out, and give it to a
friend in need, because 487SX still needed the 486SX to go through the
powerup cycle (or something like that - I forget exactly what the catch was).
The custom 486SX die did eventually come out, and from that point on, 486SXs
were significantly cheaper for Intel to make. THE JOKE WAS most motherboard
designers would have nothing to do with such planned obsolesence, and simply
designed their motherboards to accept a 486SX, 487SX, or a 486DX in the same
socket, the cpu being selected by jumpers. Our newest 486 motherboard (6
months old - a rare 486DX4/100) still has jumpers that will allow it to be
used with a 486DX,486SX,487SX, or Cyrix Cx486 as the main (and only) cpu. This
is probably why the 487SX never really took off - too many motherboards
allowed you to directly pop in a real 486DX.

So, I'm not sure how this will affect you. Yes, there was definately a 486SX
co-processor chip (the 487SX), but that is probably your least preferred
option, $$$ wise. Sounds like Intel (ITIW:) may not even make it anymore. You
may have a motherboard that will accept a 486DX directly - the best way to
know is check the manual that came with your machine, or call the guy you got
it from. Failing that, sometimes the jumper settings are silk-screened onto
the motherboard, so you may can look there to find out. Failing that, if you
have a standard footprint motherboard, you can yank out the bad old
motherboard (maybe selling it to some greatful soul with a 286/16 :) and get a
new 486DX2/66 cpu and motherboard for around $300 and get 32 bit VESA VL-Bus
slots, if you don't already have them! If you do swap motherboards, make sure
to get a motherboard that will accept your old motherboard's memory - probably
either 9 bit wide or (less likely) 36 bit wide SIMMs. But your best bet is to
upgrade to a 486DX2/66 (or AMD's great 486DX2/80, if it's out) - thats the
best bang for the buck.

Boy, I enjoyed that :) With all the bad press about the FDIV bug, I thought
this might be a good time to point out Intel's been doing silly things for a
long time. And I haven't even started about why Intel named the 486DX3/100 the
'Intel DX4'!

I better stop now, for fear of boring you to tears :)
Hope this helped.

Ben
be...@engr.latech.edu
And if my grandmother had wheels, she'd be a wagon - Scotty

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