Upper stick memory comes from dual ppro mobo.
It has slightly shifter first notch.
Anyone have knowledge about replacements, proper naming of them and are there different brands which match this standard?
The proper name is: buffered SDRAM or registered SDRAM.
Other registered sticks which I have then have notches in the same standard place.
One notch position determines voltage 3.3/5
The other buffered / unbuffered
I don’t remember how ecc worked but many times especially Compaq buffered of a certain age were also EDO
https://github.com/raszpl/sigrok-disk FM/MFM/RLL decoder
https://github.com/raszpl/FIC-486-GAC-2-Cache-Module (AT&T Globalyst)
https://github.com/raszpl/386RC-16 ram board
https://github.com/raszpl/Zenith_ZBIOS Zenith Z-386 MFM-300 ZBIOS disassembly
Dorunkāku wrote on 2026-05-24, 12:55:The proper name is: buffered SDRAM or registered SDRAM.
...except neither of those modules are SDRAM of any kind, and no Pentium Pro chipset supports SDRAM. Pentium Pro chipsets such as the i440FX don't support SDRAM, at most EDO or if older than the i440FX just FP.
Also, buffered SDRAM isn't a thing. SDRAM is registered (or not), buffered DIMMs (like this one) are older FP or EDO technology.
So if it really is for a PPro, for starters you don't want SDRAM, instead EDO or FP. Not everything in 168p DIMM form factor is SDRAM 😮
That Compaq DIMM is - as rasz_pl's diagram shows, is 3.3V buffered memory. What I'm struggling with is figuring out if it's FP or EDO - Googling those Hitachi chips isn't getting me anything useful.
The other IBM DIMM with Hyundai HY51V16404A chips is unbuffered and definitely is EDO (data sheet mentions "Extended Data out"). Great, but if unbuffered completely incompatible. In any event you need buffered 3.3V DIMMs.
As for whether you need EDO or FP buffered 3.3V DIMMs, unless someone else can unambiguously ID those Hitachi chips we need more info: which Compaq dual PPro motherboard are we talking about here? Or if you can't ID that, which Compaq system did it come from? Or failing even that, which chipset is on the motherboard?
This brings back memories! I had the exact same model back in the day. I remember the noise from the hard drive was insane, but it was bulletproof. Yes ,its SDRAM,and most of them are less than 128MB
It support CPU Pentium---PentiumII----PentiumIII
genuin66 wrote on 2026-05-25, 10:33:This brings back memories! I had the exact same model back in the day. I remember the noise from the hard drive was insane, but it was bulletproof. Yes ,its SDRAM,and most of them are less than 128MB
Neither of the DIMMs in the pic is SDRAM. And how do you know that you had the exact same model if OP hasn't shared which model he has?
