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First post, by feipoa

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I recently ordered some 128 MB EDO DIMM modules from eBay in hope of maxing out an Intel PR440FX dual Pentium Pro motherboard. The modules are buffered with parity and have 50 ns ICs. The sticker on the modules reads Smart SM572164098E6G5OE0, while the RAM IC's are OKI D51V64405E-50. I was unable to locate a datasheet for either the modules or the IC's.

On the eBay listing, they were noted to be 128 MB modules, but the motherboard reads them as 64 MB. Thus I am trying to determine if the modules are really 64 MB, or if the motherboard has some incompatibility with these modules, e.g. due to memory configuration, refresh, or whatever. Attached below is a photo of one of the modules, front and back. I did notice that the IC's on the back are flipped around, though it seems unlikely that they would be wired incorrectly.

Not sure of it matters for memory compatibility, but I am running two Pentium II Overdrive units at 333 MHz.

Smart_SM572164098E6G5OE0_with_OKI_D51V64405E-50.JPG
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Reply 2 of 63, by feipoa

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They aren't EDO SIMMs, they are 168-pin EDO DIMMs, not to be confused with 168-pin SDRAM DIMMs. The manually specifically mentions support for 128 MB async buffered EDO ECC DIMMs, for a maximum total system memory of 512 MB.

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Reply 3 of 63, by BitWrangler

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I'm fairly sure you've got 128MB on those modules, but I am not very sure on how they are arranged, at first I thought it was too many banks, but there is also a question about if it's seeing "deep" enough into each chip. For example, if they were 64Mbit, 8Mx8bits it would be 8Mbit deep on each row, if they wer 64Mbit 4Mx16bits they would be 4Mbit deep. But what I'm getting from the chip number is that they are 16Mx4bit which means 16Mbit deep, so if board only supports conventional 8Mx8 DRAMs then it's not seeing the upper 8Mbit per row.

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Reply 4 of 63, by feipoa

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BitWrangler, thank you for your reply. Indeed my fear is the board doesn't support the configuration like in your example, which may imply that the eBay listing is not necessarily incorrect and I probably would need to pay for return shipping. However, I am awaiting the spec sheet from the seller, which he said that he needs to consult with his "expert". lol. When I asked which board he tested these in, he did not reply to this effect, just that they were tested. I only have about 2 weeks left in the 60 day window to return these. They were not cheap by any means.

Based on your response, are you suggesting that I look for 8Mx8 IC's on these modules to increase the probability that they will work? Does anybody have a photo of 50 ns modules known to work on this motherboard?

EDIT: According to the motherboard's manual dated November 1996, the 128 MB modules should be of the configuration 16 MB x 72, but does not mention the acceptable row depth for the IC's.

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Reply 6 of 63, by PC Hoarder Patrol

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Datasheet & wayback page

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https://web.archive.org/web/19971022003649/ht … modules1_0.html

Reply 7 of 63, by feipoa

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PC Hoarder Patrol, thank you. The part numbers aren't identical so all I can do is speculate. The closest part number for buffered, ECC, 168-pin DIMMs is:

16Mx72         Jedec         SM5721640UUEUGU        1.250        EDO/FPM  16Mx4      -     3/5       4K/8K  

This supports BitWrangler's initial thoughts of 16Mx4 and it being "too deep", but before concluding this, we'd ideally have some case examples of known working 128 MB modules and lookup their specs.

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Reply 8 of 63, by PC Hoarder Patrol

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The legend for the "U" placeholder characters is at the end of the datasheet under 'Ordering Information'

The only 128MB module listed by Intel under tested memory seems to be this one

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Also, some 256MB modules seem to work too, according to other PR440FX threads at Vogons

Reply 9 of 63, by feipoa

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I remember there being some casual notes of 256 Mbyte modules working in past threads, but when I went looking about a year ago, I didn't find much evidence of long-term or stringent testing at 50 ns. Do you recall if there was a photo of the modules? Did the full 1024 MB work at 50 ns? Sometimes when pushing the limits like this, the speed might need to be toned down to 60 ns, which would not interest me.

Thank you for that new pdf and clarification on the part numbers. Seems odd that they would use these "U" spacers like this. Maybe I haven't seen enough memory spec. sheets. It does look like these modules are based on the 16Mbit x 4bit IC configuration. However, the other datasheet you referenced for Intel's known working modules were also based on 16mbit x 4bit. So what is the difference with those and what I have? Do you have a reference URL to those known working modules? The PDF you shared contains two 16Mx4 module possibilities, one at 4K refresh and the other at 8K refresh. Are both 4K and 8K modules listed as known working by Intel? These Smart modules appear to be 8K, however I cannot imagine this accounting for the missing memory count.

Wouldn't 8Mbit x 8bit not make sense for these modules? The memory controller is expecting 64-bits for the data (plus another 8-bits for ECC), so to arrange 64-bits, we could only have 8 ICs on the module and this would equate to only 64 Mbyte per module, not 128 MByte. For each module to be configured as 8-bits, wouldn't we need each IC to be 16Mbit x 8bit and only have 8 IC's instead of 16? 8 IC pieces x 16mbit x 8bit = 128 Mbyte.

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Reply 10 of 63, by PC Hoarder Patrol

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feipoa wrote on 2021-07-28, 07:14:

I remember there being some casual notes of 256 Mbyte modules working in past threads, but when I went looking about a year ago, I didn't find much evidence of long-term or stringent testing at 50 ns. Do you recall if there was a photo of the modules? Did the full 1024 MB work at 50 ns? Sometimes when pushing the limits like this, the speed might need to be toned down to 60 ns, which would not interest me.

Thank you for that new pdf and clarification on the part numbers. Seems odd that they would use these "U" spacers like this. Maybe I haven't seen enough memory spec. sheets. It does look like these modules are based on the 16Mbit x 4bit IC configuration. However, the other datasheet you referenced for Intel's known working modules were also based on 16mbit x 4bit. So what is the difference with those and what I have? Do you have a reference URL to those known working modules? The PDF you shared contains two 16Mx4 module possibilities, one at 4K refresh and the other at 8K refresh. Are both 4K and 8K modules listed as known working by Intel? These Smart modules appear to be 8K, however I cannot imagine this accounting for the missing memory count.

Wouldn't 8Mbit x 8bit not make sense for these modules? The memory controller is expecting 64-bits for the data (plus another 8-bits for ECC), so to arrange 64-bits, we could only have 8 ICs on the module and this would equate to only 64 Mbyte per module, not 128 MByte. For each module to be configured as 8-bits, wouldn't we need each IC to be 16Mbit x 8bit and only have 8 IC's instead of 16? 8 IC pieces x 16mbit x 8bit = 128 Mbyte.

Sorry, no pics of the 256MB modules - Re: Intel PR440FX Dual Pentium Pro 200

The Intel link (bottom of the page) - https://web.archive.org/web/20030423163818/ht … 40fx/pr_mem.htm - only lists the 1600s @ 60ns (so 4K only).

This appears to be pics of those - https://ram-co-shop.de/128-MB-EDO-DIMM-168-pi … 372F1600AK-6U_1

Assume you're on the latest BIOS (release 5.0 or later), as earlier versions seem to have had memory sizing problems.

Reply 11 of 63, by feipoa

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Thanks. That is helpful. I have a starting point now.

The refresh rate just dictates how fast the controller needs to revive the capacitative memory cell content, right? So if the motherboard is refreshing too slow for the 8K modules, then it seems like the memory would become flakey, or not work from the onset. Thus I wouldn't expect a refresh issue like this to render exactly half the memory unseen. Anyone else have experience with this? I could not locate any spec. in the motherboard manual concerning DRAM refresh rates.

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Reply 12 of 63, by PC Hoarder Patrol

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Probably loads like these as well (vendor tested) but again 60ns - https://web.archive.org/web/20010418095105/ht … FX?OpenDocument

EDIT - and clearly possible with 256MB modules @ 50ns... Another Retro Project Intel PR440FX Board

Reply 14 of 63, by Skyscraper

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This Samsung 128mb module works in my PR440FX. I also have a Siemens one with similar layout that also works. I have 4x 256mb IBM modules that I bought for this borad but I haven't tested them yet and I have no clue where they are.

The pics were taken with a phone in bad light and also got compressed (even more) by the forum software but it was the best I could do for now.

128mb edo dimm side1.jpg
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128mb edo dimm side2.jpg
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All modules I have tried can run with the 50ns setting at 70 MHz FSB.

New PC: i9 12900K @5GHz all cores @1.2v. MSI PRO Z690-A. 32GB DDR4 3600 CL14. 3070Ti.
Old PC: Dual Xeon X5690@4.6GHz, EVGA SR-2, 48GB DDR3R@2000MHz, Intel X25-M. GTX 980ti.
Older PC: K6-3+ 400@600MHz, PC-Chips M577, 256MB SDRAM, AWE64, Voodoo Banshee.

Reply 15 of 63, by Dorunkāku

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Kingston KTC-PRL/512 modules should work too. I have four of those running on a Dell PowerEdge 2100 motherboard.

This motherboard officially supports only 256MB but runs without any issue with 512MB installed.

Reply 16 of 63, by feipoa

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Skyscraper, thanks for those images. Those appear to have sixteen data 8Mx8 IC's on them. So I guess my reasoning on how the data width is added up is wrong because 16x8bit = 128 bit, not 64-bit.

It seems hard to believe that the Intel website saying that 16Mx4 work would be incorrect, so I am still confused why these OKI-based 16Mx4 modules aren't showing the full 128 MB per module.

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Reply 17 of 63, by BitWrangler

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8x8s would normally be wired as two sides (DIMM banks) of 64MB

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Reply 18 of 63, by feipoa

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I logged into eBay to return the memory and I see this note:

"Seller does not accept returns", followed by, "not elligable for eBay Money Back Guarantee", followed by, "but you can still submit a return request". 1-hour later, the seller "closed" my return.

huh? I thought all eBay purchases came with eBay's Money Back Guarantee? If the seller refuses the return, does this mean I need to go through Paypal?

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Reply 19 of 63, by maxtherabbit

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feipoa wrote on 2021-07-28, 00:29:

They aren't EDO SIMMs, they are 168-pin EDO DIMMs, not to be confused with 168-pin SDRAM DIMMs. The manually specifically mentions support for 128 MB async buffered EDO ECC DIMMs, for a maximum total system memory of 512 MB.

Whoops, I knew EDO DIMMs existed but I've never heard of actually using them so I just assumed without looking closely at the picture or reading carefully 🤣