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3 CPUs plugged into a 386 Motherboard

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DelTron

New Member
Joined
Oct 21, 2007
Messages
5
Hello I'm new to this forum.

I'd like to start by saying:

I have a 386-40 that has 3 cpu's plugged in. One is an am386-40 embedded. The next is a Cyrix Fasmath-40mhz 387 CPU. The next is a second am386-40. I installed the two non-embedded ones.

Both am386-40's are running hot. The cyrix 387 is cold. I Did not run DooM or DooM II to test the cyrix 387 temperature theory, but I can. BIOS generated startup screens and windows 95c both detect the 387, but this is a side issue.

Do you think this PC supports multiprocessing?
Windows displays "80386, 80387" under my computer->properties

My system info is as follows:

• am386-40
• am386-40
• 387-40

• 20mb RAM
• baby (?) AT board (very tiny appearance)
• 1mb trident video
• creative awe64 sound
• 400mb hdd
• 8x cd-rom
• 3.5" floppy drive
• basic peripherals - mouse/keyboard/speakers/monitor
• Turbo Button feature
• AMI BIOS 1993

thanks for your comments on this interesting topic
 
It is highly unlikely that your machine is using both of the primary processors (The AMD 386-40) together. That would have been a very very high end and specialized motherboard back in 1993.

I would remove the extra 386-40 immediately - it probably does not belong there, and it is causing extra current draw through the motherboard.
 
I doubt its capable of SMP. The earliest dual socket I've seen was a 486, and even then it was pretty hit or miss. I really doubt its multiprocessing, none of the OS's of that era would have supported it anyway.
 
Vlad said:
I doubt its capable of SMP. The earliest dual socket I've seen was a 486, and even then it was pretty hit or miss. I really doubt its multiprocessing, none of the OS's of that era would have supported it anyway.
Click to expand...
NT 3.1 supports SMP 386's ;) ..

NT 3.5 however does not.
 
The 'extra' socket may be intended for an upgrade cpu, such as the DLC. When you pop a chip into the socket it should disable the onboard 386, but a standard 386 probably doesn't. There were also other processors available in the '386 era, that would work along with the main CPU, like I/O speedups, NPUs, etc. One type was from Weitek, but I don't recall any of the others...anyone else? That would be my best guess. Look in your BIOS setup and see if there's a setting to en/dis-able the Weitek processor. The NPU should be just fine though, but as others have said, remove the socketed CPU most ricky-tick before it destroys something.

Here's a wiki to get ya started: http://en.wikipedia.org/wiki/Weitek

--T
 
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Thanks guys, I will remove the extra CPU.

After I put it in, it has had a couple days of uptime, but I agree it cannot be great for its health, as there must be a great deal of current draw on the bus. This isnt a bad site afterall.
 
additionally I'd like to note that it was indeed for a weitek co-cpu. I, for some reason believed that only one type of CPU could fit into its respective socket. I hope the extra cpu isnt burnt out :blush:

However one has to be curious if both NPU's could be enabled.
 
DelTron said:
additionally I'd like to note that it was indeed for a weitek co-cpu. I, for some reason believed that only one type of CPU could fit into its respective socket. I hope the extra cpu isnt burnt out :blush:

However one has to be curious if both NPU's could be enabled.
Click to expand...

What manufacturers did sometimes was put the 387DX pins on the inner pins of a socket, Weitek coprocessor on the outer pins (due to the pin arrangements one would not use the pins of the other; It also effectively prevents the two NPUs to be used at the same time). A 386DX would however use the same pin areas in a socket, and I'm pretty sure it is a different pinout for those areas. There is nothing preventing a Weitek and 387DX NPU from functioning on the motherboard, since the means to address them, and quite a bit of the functionality, is different.
 
DelTron said:
However one has to be curious if both NPU's could be enabled.
Click to expand...

Can't help ya there. I've never even seen one in the wild, I've only heard/read of them. OTOH, a '386DX & Cyrix FastMath combo should be just about all you need for vintage computin'. I can't see where adding a second NPU would gain any noticeable performance.

--T
 
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I don't recall which variation of UNIX it was, but back in high school, we had a "mini-supercomputer" that had 8 386-387 pair's in it. (And an incredible 24 MB of RAM, and over 1.5 GB of total hard drive space! :p)
 
I highly doubt that you plugged your 386 into the weitek socket by accident. The Weitek sockets are slightly smaller, and it is not physically possible to insert a 386 chip in there. I have a 386 motherboard that is similar to yours. It has an embedded am386 40MHz, an FPU socket, and an extra 386/486DLC ceramic socket. So far, I have not been able to get my extra CPU socket to work. Unlike yours, my extra CPU does not get hot at all...I tried both 386 and 486DLC. My guess is that the CPU in the socket cannot function while the embedded one is present. I think that the manufacturer was just careless and soldered on the extra socket when it wasn't needed or usable. You have to keep in mind that these motherboards were made by el cheapo companies long after the glory days of the 386.

Concerning the Weitek chips, I have found that just because your BIOS has an option for it doesn't mean that your motherboard is able to accept one. I have several 386 and 486 boards with Weitek settings in the BIOS and no way of physically plugging it into the motherboard. There is no extra row of pins on the 387 socket, nor any additional solder pads on the motherboard. Perhaps there was some kind of adapter available. Also, it is very possible to have both Weitek and 387 FPUs installed at the same time. I found a nice italian website a few months back with a guy who did very thorough testing. See if you can find it on this page:

http://www.cpu-museo.it/

You should be able to find two setups on the page. One has a combination rapidCAD and 3167, and the other is part of a motherboard from an HP 386 machine that has 386, 385, 387 AND 3167.

...and finally, there is one other chip that can use the Weitek socket. It is called the Cyrix EMC.
 
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Thanks ananymous Coward. You must type fast because login times out a bit too soon for me. The weitek 387 is indeed 121 pins, not 132 like the 386. http://www.cpu-world.com/CPUs/3167/index.html. Confirms how the 387 works along side the weitek, which enhances CPU performance even further.

Yes, I think the mobo manufacturer was careless when placing the extra socket on the board, as 386's were budget PC's with budget components in 1993.

additionally I'd like to comment on Ananymous freak's post, that I like this machine he's talking about. when was that?

im willing to research exactly what this extra socket is, and i'll keep you guys posted. Thanks for the information, the guru here are very resourceful.
 
Two math coprocessors is not faster than one.

The main CPU is going to talk to exactly one math coprocessor. The other one is surely being disabled. If you read the Intel specs for these things, it's not possible to have two active at the same time working with one processor.
 
Just a picture of my 386's strange mobo

Just a picture of my 386's strange mobo

386d.jpg
 
DelTron said:
386d.jpg
Click to expand...

That is interesting. It's definitely not a 486 socket, definitely a 386-style socket. Yet the board includes a 40 MHz 386 soldered, and no faster 386s were ever available, so it's not like it was meant to be an upgrade socket.

You mention that it runs power, but "doesn't seem to do anything". Have you tried running some basic benchmarks with the stock chip, and with, say, a SLOWER 386 in the socket to see if it will use the socket if you have a chip in there?
 
That motherboard was designed so that they could either solder on a CPU (permanent) or leave it off and use the processor of choice.

When it was first introduced they probably use whatever processor the customer wanted, at the end of its life the 40mhz part was probably the only one available and they just had it surface mounted by defaut.
 
Unknown_K said:
That motherboard was designed so that they could either solder on a CPU (permanent) or leave it off and use the processor of choice.

When it was first introduced they probably use whatever processor the customer wanted, at the end of its life the 40mhz part was probably the only one available and they just had it surface mounted by defaut.
Click to expand...

Since they had to use the effort of surface mounting the processor at time of motherboard manufacture, why wouldn't they just leave off the socket?
 
Please also remember that at that time there was an awful lot of chip-supply-paranoia, it was only a few years earlier that IBM had bought up the whole world's supply of TTL chips, taking the price of e.g. a 7400 from about 11p to over a pound overnight. People were designing for multiple suppliers of key components just so the products could continue to be manufactured if supply of the preferred component dried up. it's true!!!!
 
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