Help with my 486 system

[Mameotron]

First, this really doesn't have anything to do with MAME, but I know a lot of people here have extensive computer expertise.  Any help wouold be really appreciated.

Recently I was given a fully working 486SX system.  This is interesting for me, since back in the day (1990) I had a very similar system I worked on daily.  I have a software collection I legally purchased way back then (AutoCad release 14 and lots of surveying software) and I thought it would be cool to get it all running on my new 486SX.  I've installed everything from my * 5" floppies!! * and it all looks like it is intact.  Now for my questions.

AutoCad won't run, because apparently it looks for a math coprocessor.  It won't even try to run if it can't find one.  According to the manual that came with my 486sx, you can't just plug in a coprocessor.  You have to upgrade to a 487SX chip, which has the built in coprocessor.

I haven't been able to find a 487SX chip anywhere, even on e-bay.  Are they really that rare?  If they are, I don't want to spend a lot on it.

Another thing I wanted to try:  I remember back in the day you could find a software hack to make autocad think you had the coprocessor installed when you really didn't.  I have also had no luck finding this today.  Anyone ever heard of it?

Along those same lines,  just for fun I tried installing that old version of Autocad on my p4/2.0 Ghz box, and it wouldn't run because it couldn't find a math coprocessor!  Is there a way I could get this to run on my current setup?  I'm not really trying too hard on this, it's just one of those 'just because I can' type things.

Thanks in advance for your input.

[Tailgunner]

Does the board support 486 DX chips? DXs also have the built in co-processor and you'l have much better luck finding one of them. I picked up a complete 486DX-133 system for $10 at a thrift shop recently.

[Mameotron]

Ah! Yes, I just checked the specks for the board.  There are four jumbers to set, depending on the type of processor you install.  It does support 486 DX.

Thanks, I didn't know the 486 DX had the built in coprocessor.  I have seen lots of them on e-bay.

[Tailgunner]

As I remember, Intel started building the FPU into the processor with the 486 series chips. They had some issues with the early 486 chips that led to the SX and DX designations. Chips that failed the floating point test had the co-processor burned out and the chip was sold as an SX. Chips that passed were sold as DX chips at a higher price. The SX chips were continued for laptops and such after Intel solved the FPU problem, but they were never popular and are quite rare.

While you're at it, I'd suggest archiving everything you've got on 5.25" floppy to either CD or at least 3.5" floppy. I'm not surprised that the disks are still good, I've still got boxes of 8" floppy disks holding data that's over 20 years old. Working 5.25" disk drives are tough to come by these days, and once the drive is dead the disks are useless.

[Trenchbroom]

The best site for CPU history, Red Hill, calls it this way:

"The 486SX was a strange beast. Essentially, it was a 486DX with the maths co-processor disabled. This involved one extra step in the manufacturing process, so the 'cheap' 486SX actually cost more to make than the 'expensive' 486DX! The SX was developed mostly for marketing reasons

[Mameotron]

Wow.  Thanks for the history.  It seems incredible that those chips sold for $400, and I just bought one on e-bay for $2.

[Tailgunner]

I remember being more than a little preturbed when my bro's AMD 386DX-40 got better frame rates in Strike Commander than my Intel 486DX-33.

That $400 is in Aussie dollars, they were around $200 here in the states. Also, at the time $300 would buy you 8 megs of system memory, and $200 would buy you a 200 meg hard drive.

[jlampc]

On some MB's they had 2 sockets one for the SX chip and one for the optional Co-processor. The real funny thing is that a 487sx chip is not a Co-processor at all but a 486dx chip. When you put it in the second socket, the board disables the first socket  and the 487sx takes over as the CPU. You said your system takes a DX...That should be a lot easier to find...Good Luck.

[Mameotron]

AHHH!  Got my 486DX chip in the mail today.  After resetting the jumpers, installing the correct VGA drivers, and reconfigureing AutoCad, I'm good to go!!  Now I just need to throw on some Frankie Goes To Hollywood, boot up Donkey Kong on my Mame cab, and I'm right back in the 80's!!!!

[Pipercub]

Depending on the power handeling, multipliers, and freqs, you may be able to use an AMD DX4 100 or one of the various AMD and Cyrix etc. pentium class chips that fit the socket.