Hi
I have a few 72 pin simms around and I cannot make any PC work with them
I have googled a bit and they seem to be assossiated with IBM PS/2 machines
So does it mean that these are specific for PS/2 systems and are incompatible with normal IBM PCs ?
that is so weird
thanx for the help
These are 72p SIMMs. They are rather old, slow ones though, which might be a problem, and in newer systems SIMMs need to be placed in identical pairs yet this is a mixed bag.
72p SIMMs were first used in PS/2 systems, so were at one point referred to as "PS/2" memory. IBM PS/2 systems can be very picky regarding their memory. One of these SIMMs is IBM-branded and may be from PS/2s, but the others definitely aren't, one being 'Topless', the other is Siemens-branded. I know those Topless SIMMs. They are technically unimpressive, but are broadly compatible with anything that runs slow enough to work with them.
Not sure what to do with your comment about the IBM PC. The IBM 5150 PC is much older than the PS/2 and this memory and uses DRAM DIP chips stuck directly on the motherboard. That's probably not what you are referring to as "normal IBM PC", but it's not clear what it would be. It would help us help you if you could tell us exactly what system you are trying to use this memory in.
dionb wrote on 2025-03-07, 22:15:That's probably not what you are referring to as "normal IBM PC", but it's not clear what it would be.
By "Normal IBM PC", I took it as meaning IBM compatible, which means pretty much any PC that takes (in this case) 72 pin SIMMs. Can't answer the original question though, other than to say that it's pretty common to find SIMMs that are dead.
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dionb wrote on 2025-03-07, 22:15:These are 72p SIMMs. They are rather old, slow ones though, which might be a problem, and in newer systems SIMMs need to be placed in identical pairs yet this is a mixed bag.
72p SIMMs were first used in PS/2 systems, so were at one point referred to as "PS/2" memory. IBM PS/2 systems can be very picky regarding their memory. One of these SIMMs is IBM-branded and may be from PS/2s, but the others definitely aren't, one being 'Topless', the other is Siemens-branded. I know those Topless SIMMs. They are technically unimpressive, but are broadly compatible with anything that runs slow enough to work with them.
Not sure what to do with your comment about the IBM PC. The IBM 5150 PC is much older than the PS/2 and this memory and uses DRAM DIP chips stuck directly on the motherboard. That's probably not what you are referring to as "normal IBM PC", but it's not clear what it would be. It would help us help you if you could tell us exactly what system you are trying to use this memory in.
Hi !
thank you for you reply guys
Yeah, when I am referring to IBM PC I am of course referring to all the clones compatible with the IBM PC architecture
My question is simply if someone recognizes this Simm modules as exclusive to PS/2 models or all Simms are the same
I cannot make them work on any motherboard of "clone" PCs being it a 486 or pentium
I see information online mentioning the PS/2 machines are picky about their RAM, what I cannot understand is if it is the SIMM module that has to be specific to PS/2 or it is the other way around, i.e. all "clone" PC simm modules run on most PCs but only certain ones are accepted on PS/s systems
I know that broken simms is a thing but I find it strange that "weird" looking simm modules like this ones are all broken and all my "normal" looking simms work more or less ok
thanx ! 😀
Yes, the IBM branded SIMM is definitely compatible with certain IBM PS/2 Models.
It hat parity and presence detect what makes it compatible.
It will at least work with the 486 Models 76, 77, 90 or 95.
The 386 model 70 uses smaller and slower 2MB 85ns modules, not sure about the sx and slc Models 55, 56 and 57?
https://eprm.ardent-tool.com/eprm/f232.htm says tit will work in the 56/57
Topless means the chips do not have complete/any housings, often the die is glued directly on the pcb with just a blob of glue covering the chip.
These were often made from second choice chips and therefor cheaper than branded modules.
Nunoalex wrote on 2025-03-11, 13:39:Hi ! […]
dionb wrote on 2025-03-07, 22:15:These are 72p SIMMs. They are rather old, slow ones though, which might be a problem, and in newer systems SIMMs need to be placed in identical pairs yet this is a mixed bag.
72p SIMMs were first used in PS/2 systems, so were at one point referred to as "PS/2" memory. IBM PS/2 systems can be very picky regarding their memory. One of these SIMMs is IBM-branded and may be from PS/2s, but the others definitely aren't, one being 'Topless', the other is Siemens-branded. I know those Topless SIMMs. They are technically unimpressive, but are broadly compatible with anything that runs slow enough to work with them.
Not sure what to do with your comment about the IBM PC. The IBM 5150 PC is much older than the PS/2 and this memory and uses DRAM DIP chips stuck directly on the motherboard. That's probably not what you are referring to as "normal IBM PC", but it's not clear what it would be. It would help us help you if you could tell us exactly what system you are trying to use this memory in.
Hi !
thank you for you reply guys
Yeah, when I am referring to IBM PC I am of course referring to all the clones compatible with the IBM PC architecture
My question is simply if someone recognizes this Simm modules as exclusive to PS/2 models or all Simms are the same
I cannot make them work on any motherboard of "clone" PCs being it a 486 or pentium
Arguably the PS/2 is PC compatible too 😉
But when it comes to RAM, it pays to be specific. Exactly which 'any' motherboards are you using?
This is 70ns RAM, so anything over 60MHz won't work. The Siemens-branded topless SIMM is non-parity so won't work if parity is required, the other two are parity SIMMs which should work whether or not parity is required, but some BIOSs refuse parity memory if set to non-parity. And Pentium? The vast majority of Pentium chipsets require memory to be installed in identical pairs. and these are three different (4MB with parity, 4MB without parity and 8MB with parity).
I see information online mentioning the PS/2 machines are picky about their RAM, what I cannot understand is if it is the SIMM module that has to be specific to PS/2 or it is the other way around, i.e. all "clone" PC simm modules run on most PCs but only certain ones are accepted on PS/s systems
PS/2 systems can be picky with their RAM, but so can other systems. With zero information on the other systems can't comment here. PS/2 defined the 72p SIMM spec, so normally SIMMs that work in PS/2 systems will also work in non-PS/2 systems.
Aside from regular 72p SIMMs, some PS/2 systems used proprietary 30p SIMMs (the early 808x models) and some used proprietary ECC SIMMs. But please, stop using vague generalizations. Specific machines have specific requirements and specific SIMMs work in them. There are very many PS/2 systems, each with their own idiosyncrasies. Only one of these three SIMMs is an IBM one.
You can look up the P/N of that SIMM and see it's a regular parity SIMM. No ECC weirdness, so it will work in other systems.
I know that broken simms is a thing but I find it strange that "weird" looking simm modules like this ones are all broken and all my "normal" looking simms work more or less ok
Again, please specify the exact boards you were trying these SIMMs in and at what speeds. They are old and low-end, trying to run them past their limits is more likely reason they fail than because they look "weird".
In particular the 'Topless' SIMMs are pretty bulletproof in my experience. I utterly abused a pile of them a couple of decades ago (made a necklace out of them, found a willing young lady, did a photo shoot 😉 ) and every single one still worked fine.
