Help identifying an unusual expansion slot

I've been out dumpster diving again... and this time I ended up lucky and scored a 386/486 hybrid motherboard that has both a 386 slot, and a 486 slot, which is currently populated with an intel 486 DX2-50.

Anyway, the point of this thread is this motherboard seems to have an unusually long ISA slot, which I have never seen before in my years of looking at computer motherboards.
My first thought was that this might be for some kind of riser card, but typically motherboards that are designed to use riser cards only have one expansion slot: the riser card slot, and this one has several normal 16-bit ISA slots as well, so I'm kind of stumped here.

An image of the motherboard is below.
If the image is too large for forum standards, I can re-size it down further, just let me know.
The odd slot in question is circled red.



Any help would be appreciated.

EDIT: If you want to see a rather large high-resolution image of this, you can click here, but be warned, it's 2.2mb: http://www.outfoxed.net/386-486/r_DSC00474.jpg

That slot looks like it is for a 32-bit memory expansion card, very common on 386 motherboards. See http://artofhacking.com/th99/m/C-D/32957.htm for a Diamond Flower model with a similar connector. I haven't seen too many 486 motherboards with that type of slot. I wonder how it would perform.

Hrmm, I've had 286 systems in the past and an old MFM-based system that was very early 286 based but this is my first actual 386-era motherboard I've ever owned, and so I have limited / no experience with 386 systems and as such have never heard of memory expansion boards for 386's. Did they add more 30-pin SIMM slots some how to expand system RAM?

And it works perfectly, came with a 16-bit video card, 8-bit serial card, and a 16-bit IDE card and It booted up and ran windows 95 that came pre-installed on the hard drive.

And apparently it supported 16mb simms too because it came fully populated with 96mb of ram (16mb x 6). I've since swapped the memory for 4x1mb simms and plan on selling the 16mb ones on ebay, and possibly selling this board as well but I'd like to figure out just what I actually have here before selling it.

A 386/486 motherboard that supported 96MB of RAM and looks like it should go to 128 MB with the memory slots on the motherboard. Wow. That is one impressive board.

A memory expansion card would as befits the name are filled with memory sockets or slots. Some had cheaper older memory than was on the motherboard so a motherboard similar to yours might be outfitted with 8MB in SIMMS and a card stacked to the gills with 16MB of socketed chips. It was a strange time. Some systems could not use the memory card if the motherboard had large capacity SIMMs; the system would only recognize so much memory and the expansion card gets ignored. Basically, works the same as expansion cards for the 286 but the wider bus keeps from starving a faster CPU.

I was not expecting the system to support that much memory. Usually, 386/486 supported 64MB or less and often only 32MB of that was on motherboard which means another 32MB might be on the expansion card. It is possible that I was wrong and the slot is a more general purpose one like a VLB precursor. It should still be a 32bit slot and finding a matching card will be very challenging.

Oh c'mon...just look at the outlines in TH99 and match it up.

You've got a NIC Technology UNH433L motherboard. If you look at the notes, the "long" slot is a proprietary 32-bit expansion slot. I suspect it's for a disk controller or a video card, but I don't think we'll ever know. This board probably came before the adoption of VLB.

Chuck(G) said:

Oh c'mon...just look at the outlines in TH99 and match it up.

You've got a NIC Technology UNH433L motherboard. If you look at the notes, the "long" slot is a proprietary 32-bit expansion slot. I suspect it's for a disk controller or a video card, but I don't think we'll ever know. This board probably came before the adoption of VLB.

Click to expand...

I saw that and it's similar.. but no embedded 386 processor on mine. CONFIGUS ms-dos utility reports this motherboard's BIOS ID string as SIGMA COMPUTERS, I don't find much googling that so I'm not really sure if that's who made the motherboard or what, but.. bleh.

And a 32-bit slot this long? I've never heard of or even seen such an animal, but I suppose it might be possible.

krebizfan said:

A 386/486 motherboard that supported 96MB of RAM and looks like it should go to 128 MB with the memory slots on the motherboard. Wow. That is one impressive board.

<snip>

I was not expecting the system to support that much memory. Usually, 386/486 supported 64MB or less and often only 32MB of that was on motherboard which means another 32MB might be on the expansion card. It is possible that I was wrong and the slot is a more general purpose one like a VLB precursor. It should still be a 32bit slot and finding a matching card will be very challenging.

Click to expand...

Yeah.. I know most of these boards support 64mb max, imagine my surprise when I powered it on and the ram kept counting past 64 mb, on into the 70's, 80's.. then stopped at 98,304 kb.

I'm reading some of the labeling on this motherboard and one of the jumper settings says.... 80487SX... what actually is a 487? I found some info on it on CPU WORLD, and it's some kind of math co-processor? Is it possible this motherboard supports using a 386 DX AND a 487 for floating point at the same time?

I don't see the difference other than the one shown on TH99 uses the SMT version of the 386DX and yours has a socket for a 386DX. No practical difference since you have to change jumpers. Otherwise, as far as I can tell, the jumpers and connectors are the same.

The 32-bit slot as stated is proprietary. That means that NIC manufactured something to go into the slot, but that's lost in the murk of time. It might well be that plans for an expansion card were scrapped by the time the board hit the market.

There's nothing "embedded" about the 386--the SMT board mounts it permanently, you have a socket. You can't use both a 386 and a 486 at the same time on this board.

Don't let the "Sigma" fool you. The board was made in Taiwan and could well be OEMed to a number of companies.

I didn't ask about 486 at the same time... I asked about 487... I don't know much about the 487, but apparently it wasn't a "real" processor like the 486, it was just a math co-processor? I'm not sure and just speculating.

kithylin said:

I'm reading some of the labeling on this motherboard and one of the jumper settings says.... 80487SX... what actually is a 487? I found some info on it on CPU WORLD, and it's some kind of math co-processor? Is it possible this motherboard supports using a 386 DX AND a 487 for floating point at the same time?

Click to expand...

487SX was one of Intel's stranger ideas. It is a complete 486 including coprocessor which was designed to go into a motherboard that already had a 486SX installed and then the 486SX would be turned off and all the work would go through the 487SX. A hugely complex method of adding floating point because 486SX lacked floating point. I suspect that this motherboard was designed to fool a 487SX into thinking it was on a proper motherboard. That way, either a 486DX or 487SX could be installed depending on which was cheaper at the moment of assembly. The net result would be one reasonably fast system with floating point. Only one CPU would be active though; it might be possible to set the jumpers so that the 386 runs and 486/487/other does not.

One short aside: Not every motherboard with 32bit slots ever had any cards to go with it. Sometimes, it was more a marketing gimmick for the future because the competition had the same.

krebizfan said:

487SX was one of Intel's stranger ideas. It is a complete 486 including coprocessor which was designed to go into a motherboard that already had a 486SX installed and then the 486SX would be turned off and all the work would go through the 487SX. A hugely complex method of adding floating point because 486SX lacked floating point. I suspect that this motherboard was designed to fool a 487SX into thinking it was on a proper motherboard. That way, either a 486DX or 487SX could be installed depending on which was cheaper at the moment of assembly. The net result would be one reasonably fast system with floating point. Only one CPU would be active though; it might be possible to set the jumpers so that the 386 runs and 486/487/other does not.

One short aside: Not every motherboard with 32bit slots ever had any cards to go with it. Sometimes, it was more a marketing gimmick for the future because the competition had the same.

Click to expand...

Aha... Thank you for clearing this little bit of confusion up for me. I've never actually seen any reference to "487" until today on this motherboard so I was kind of scratching my head and trying to discover information.

The 486SX was a whacky idea. It did have a (sometimes good) NDP on it, but it was hard-disabled. Read about it.

Chuck(G) said:

The 486SX was a whacky idea. It did have a (sometimes good) NDP on it, but it was hard-disabled. Read about it.

Click to expand...

I don't think it was too wacky, kind of smart for Intel actually. The processors with a defective floating point unit could be re-sold and still make money off of them instead of outright chunking em in the bin. It did make it rather confusing for consumers though I'm sure. And I remember now thinking back my packard bell we bought brand new in 1995 came with a 486 SX-33 in it, and no cache. I remember what a big difference just adding cache to it did... and sad we ever got suckered into buying a packard bell, I knew very little of computers back then.

It was a horrible idea when word got around that Intel was selling what amounted to defective chips--working or not, corporate buyers stayed away from 486SX systems. Intel never did that again. They'd done it before with the 2109 DRAMs.