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Pentium 133 board question

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KD2IXL

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Hello all again,
I received a 1997 pentium 133 machine and have a question about the motherboard. I can’t find any model code online. It has 3 SIMM slots but beneath it it also appears to have 2 DIMM slots. Was this common for this generation of Pentium? Can all the slots be populated or is it either the SIMM or the DIMM? Does anyone else have a machine like this?
Thanks,
Ian
 
It can't have 3 SIMM slots as SIMMs work in pairs. So it's either 2 or 4 SIMM slots.

I have a board with both SIMM and DIMM slots. The manual shows some configurations with both SIMM and DIMM memory together however it notes that the manufacturer does not recommend mixed mode usage.
 
KD2IXL said:
Hello all again,
I received a 1997 pentium 133 machine and have a question about the motherboard. I can’t find any model code online. It has 3 SIMM slots but beneath it it also appears to have 2 DIMM slots. Was this common for this generation of Pentium? Can all the slots be populated or is it either the SIMM or the DIMM? Does anyone else have a machine like this?
Thanks,
Ian
Click to expand...

Try matching it up here: https://stason.org/TULARC/pc/
 
A picture and the chipset information may help the rest of us identify the board.

Is one memory slot separated from the rest? It may be a COAST socket for cache instead of a RAM socket.
 
Stone said:
It can't have 3 SIMM slots as SIMMs work in pairs. So it's either 2 or 4 SIMM slots.
Click to expand...

This was only true of 30 pin SIMMs, but is not true of 72pin simms. I have some 486 boards that can run with a single 72pin SIMM in them.

In general most boards that have support for both generally won't allow for both to run together, and even if they do there would be some sort of tradeoff, usually in performance (ie the faster DIMM modules would be forced to run at the speed/refresh rate of the SIMMs). OP plan on one or the other, but I'd recommend the DIMMs and not the SIMMs.

EDIT: As Stone points out below, in general Pentium boards needed 72pin SIMMs to be installed in pairs. If your board has 3 of these sockets, then it maybe one of the few exceptions to this rule.
 
Last edited:
Stone said:
Pentium boards require pairs and this is what the OP has.
Click to expand...

That's not entirely true. Maybe it applied on early Pentiums chipsets or was the most common case, but definitely not a generic rule. Also this is clearly a late socket 7 motherboard as it has DIMM sockets.
I've only seen this on boards with 2 SIMM + x DIMM sockets like lutiana said to be fair, I've never seen 3.
 
Last edited:
konc said:
That's not entirely true. Maybe it applied on early Pentiums chipsets or was the most common case, but definitely not a generic rule. Also this is clearly a late socket 7 motherboard as it has DIMM sockets.
I've only seen this on boards with 2 SIMM + x DIMM sockets like lutiana said to be fair, I've never seen 3.
Click to expand...
Yes, it is true. The 'pairs' referred to SIMMs and all Pentiums require two SIMMs to complete a bank. DIMMs were not part of the discussion here.
 
Stone said:
Yes, it is true. The 'pairs' referred to SIMMs and all Pentiums require two SIMMs to complete a bank. DIMMs were not part of the discussion here.
Click to expand...

Maybe I wasn't clear, I've had a very late socket 7 motherboard with 2 SIMM sockets (+DIMMs but as you said it's irrelevant) that works with 1 SIMM installed. Uncommon? Sure. But it exists.
 
Though without more information from the OP, it will be difficult to ascertain the specifics of that board. Might be a mistake in the description, might have a slot to nowhere or a slot that isn't for main memory, or might have a memory controller able to use of an odd number of SIMMs.
 
Stone said:
Pentium boards require pairs and this is what the OP has.
Click to expand...

Some chipsets can run in "gimped" mode with one stick and half the memory bus width at a significant cost in speed. I've had several 386/486/Pentium boards which could do this.

The performance impact was pretty noticeable, it's not something I'd recommend today since those old memory modules are generally pretty cheap.
 
I miscounted since one was hidden. It does have 4 SIMM slots, though I didn't know that they had to work in pairs since I have used exclusively DIMMS. It is late and I would have to open the machine back up to take pictures of board to attempt to ID it. I'd like to figure out more about the board since it is in a bit of an obscure PC. I will post pictures of it tomorrow afternoon.
Thanks,
Ian
 
It is quite simple actually.

The required number of bits depends on the processor chipset:
- 80286, 80386SX: 16 bit wide memory bus
- 80386DX, 80486, Pentium Overdrive: 32 bit wide memory bus
- Pentium, Pentium Pro: 64 bit wide memory bus

The 486 processor (not the 386!) supports 8/16/32 bit wide busses natively, so chipset support for narrower accesses is trivial. I have never seen a mainboard support this, though.

The provided number of bits depends on the memory module:
- 30-pin modules cover 8 bits. SIP or SIMM, FPM or EDO.
- 72-pin modules cover 32 bits. SIMM, mostly EDO (older ones FPM).
- 168-pin modules cover 64 bits. DIMM, SD-RAM.

Easy to distinguish as well:
- 30-pin modules have no notch
- 72-pin modules have one notch
- 168-pin modules have two notches
 
Don't forget about the weird memory modules that look like or are similar enough to normal memory modules but aren't.

64/68 pin SIMMs. Former was a special weird memory used on the Macintosh IIfx, latter was used as display memory on several Mac 68k machines. These modules are rare enough today to be hard to stumble upon by accident.

168 pin EDO DIMMs. Also a weird Apple specific memory, used in the Power Macintosh 6400/6500 and several other models. These are identical to normal 168 pin DIMMs except for the notch in the middle of the stick being in a slightly different position. A dedicated person could force this into a normal memory slot, which would result in fire/smoke. Likewise, installing a normal DIMM in a mac will yield a similar result.

Also, many 486 chipsets do not like EDO memory and either only work with FPM or have compatibility issues. Some systems may fail to boot with EDO, not be able to count all available memory properly or have a reduced maximum memory capacity. I have one 486 machine which only supports 32 MB of EDO (2 x 16M), but 64M of FPM (2 x 32M.)
 
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