RAM suitability

[JBUK]

I have just acquired a 256mb stick on ebay. It wont work in the T20. The T20 wont boot and just freezes after initial power on. No beeps, no floppie access, nothing.
If I put it into a 390e then it will work but as if it was a 128mb stick. In a 390X it fails in the same way as in the T20

So is it faulty above 128mb or is it just not compatible. The seller is saying T20 needs high density - [quote "Thanks for the info. It's well known to me that the T20 is among a group of laptops that need high-density, which is usually identified by 8 chips each side. It seems to be because of a bank addressing limit of 128mb, so if a 256mb module has a single bank of 256mb, rather than 2 banks of 128mb, which the 16-chip modules tend to have, then the T20 won't address over the total 128mb. Trust me, whatever the cause, I've often come across this spurious compatibility and I've found the 16-chip modules are the only ones that work, rrespective of what's marked on the chip."]

The stick supplied has 4 chips per side as do all the other sticks in my Thinkpads.

Anyone have any input to help me persuade the seller that the SDRAM is faulty ??

[rkawakami]

My understanding is that the T20 is setup to use PC100 (or some PC133) modules. I would say that the system should use LOW density modules (16 total, 8 per side) as opposed to the high density version. (For more information about the differences between them, consult this thread. Ignore the silly stuff towards the end... ).

The 390E uses PC66 memory, while the 390X uses PC100. Both "errors" appear (to me) to be due to the fact that the 256MB high density module you just purchased requires a different refreshing specification than what the 390E, 390X and T20 systems use. If you replace that module with a PC100 CL2 (CAS latency 2) low density version, you shouldn't have any problems.

By the way, what are the markings on the module? Part number, written descriptions, etc. would be helpful.

[tfflivemb2]

Ray is correct. It should be PC133 or PC100 Low Density sticks (16 chips, 8 on each side) The other sticks that you use have 4 on each side, but are they only 128MB sticks? 128MB Low Density sticks will only have 4 on each side. The reason that the 390 might read it, is because the FSB is 66MHz, and you are most likely using 133Mhz chips. It will sometimes read half of it, because 133 is twice that of 66mhz. Make sense? I took me a while to learn that one.

[JBUK]

Thanks for your input guys.

It seems to me that you are saying that the 256 stick should have 8 chips per side and be low density.

Well looking at the Crucial site.....
http://www.crucial.com/store/mpartspecs ... 24A5CA7304

The ram there is shown as 32mbx64 per chip and 4 per side. I know that ram suitability is a minefield but I have a 256 stick in my 390X - this has 4 chips per side at a density of 32mb per chip. I do not doubt that this stick would work in my T20.

My failing (?) ram has V54C3256804VT8 and Vitelec on each chip

[rkawakami]

My failing (?) ram has V54C3256804VT8 and Vitelec on each chip

Ouch! (Full disclosure: I work for Mosel Vitelic, a merger of two separate companies Mosel and Vitelic over a decade ago). I'll have to dig out an old datasheet and find out what's on that puppy. Are there any other labels on the module?

[rkawakami]

I looked at our 2001 CD databook and found that the V54C3256804VT8 part is a 32M x 8 SDRAM (i.e., 256Mbit or 32Mbyte). So eight of them on a module would make it a 256Mbyte module. However, the refresh spec for this part is 8192 cycles/64ms, which I think puts it outside of the 390 and T20 machines. I believe that those chipsets use the "low density" refresh spec of 4096 cycles/64ms.

I think I may have misled you by saying you have to have "x" number of chips on the module. The number of chips on the board only is important when talking about the TOTAL memory size (128MB, 256MB, 512MB or 1024MB). You have to take into account the number of chips AND the total memory size to determine if you have "low" or "high" density memories. For example, a 256MB low density module will have 16 16Mbit memories on it. A 128MB low density module could ALSO have 16 devices on it (16 x 8Mbit). More likely, the 128MB low density module will have 8 16Mbit devices. If you have a 128MB module with only 4 devices on it, then that would be considered a high density module (4 x 32Mbit). The important point in all of this math is the realization that low density equals a 16Mbit device (or smaller) and high density is 32Mbit (and larger) memory chips. Again, it gets back to the difference in the refreshing specifications between those two densities.

I don't believe that the rated speed (PC66, PC100, PC133, etc.) has anything to do with how much memory is addressed (or "found" by the system). Not knowing exactly what the BIOS and/or chipset is doing inside the laptop, I can only say that the bus speed of the memory system merely says how FAST it's being accessed, not how much. That some laptops report "half" of the actual memory seems to me to be directly related to the refresh specification. The 16Mbit memory requires 4096 refresh cycles every 64ms. The 32Mbit memory requires double, 8192, within the SAME 64ms. What happens when you put a memory that requires 8192 cycles in a system that only generates 4096 cycles? HALF of the memory is being refreshed correctly. Well, actually, truth be told, ALL of the memory is being refreshed at TWICE the maximum refresh specification. In other words, you are violating the tested operating parameters of the device and no guarantee can be made of retaining data properly.

[vlyne]

This is all getting a bit much for my limited memory so I've tried to summarise:

Model T20 T21 T22 T23
PIII CPU 650-750 750-850 800-1000 866-1200
Chipset 440BX 440BX 440BX 830MP
Type SDRAM SDRAM SDRAM SDRAM
Pins 144 144 144 144
Form SODIMM SODIMM SODIMM SODIMM
Base 128Mb 128Mb 128Mb 128/256Mb
Max 512Mb 512Mb 512Mb 1024Mb
Latency CL2 CL2 CL2 CL3?
Speed PC100 PC100 PC100 PC133
(crucial.com PC133 works)
Chip/side 16Mbit ( multiply by 2 for 8Mbit - uncommon)
128Mb 4 4 4 4
256Mb 8 8 8 8

Drats! The columns all line up when I type it in the editor but they don't display properly?? Not sure what's going on...someone please correct this for me!
As for content, correct/add as necessary.

Cheers

[JBUK]

I have now returned the ram to the seller. He is going to"test" it and let me know the results.

Thanks all for the comprehensive help. It is refreshing to know that expertise exists on this arcane subject.

It seems to me that the memory industry has not really got its act together as far as standardising their products. This results in the user/buyer being unable to know if a stick of ram will actually work in their PC. That is unless it is bought new from the likes of Crucial.

[cinemafia]

I'm about to score a pair of 256MB Micron MT8LSDT3264HG-133's for my T20. From the spec sheet on the site I'm not sure whether they're low or high density. Otherwise, the only difference I can see between this and what Crucial offers for the T20 is that it's CL3, as opposed to CL2...though AFAIK that shouldn't matter. I hope they work...