Be careful when buying ram, it's not what you think it is!

[mike-s]

Obviously this goes without saying, but my little adventure has a twist i wasn't expecting.

I have an IBM R30, i went and bought some low density ram as i figured that this was my best shot for getting 1gig of ram in my laptop. Unfortunately the ram wouldnt work when i popped it into my laptop. Initially i started worrying about faulty memory and started some serious Investigation into any alternate possibilities last nght and as of five minutes ago i FINALLY have my answer, Density. It's not that im trying to put high density memory in a low density laptop, but rather the other way around!!!

The memory i was putting in was 32M x 16 (8 chip x 2 sodimms = 1gb), however according to this
document and this pdf, i need High density ram instead. The irony is i deliberately AVOIDED High Density ram for a fear of a compatability issue.

From IBM:

Technical specifications
Performance specifications as known at time of announcement
* PC133 Synchronous DRAM (SDRAM)
* Non-parity mode organized as 8M x 64, 16M x 64, 32M x 64 and 64M x 64 respectively
* Serial presence detect/decode
* 144-pin JEDEC/JEDIA standard SODIMM interface
* Gold-plated leads



From the PDF

Features:
¨ High density: 512 MB (64M x 72) ECC



Now to try and convince the seller i need a swap or refund........

[proaudioguy]

I don't know enough about the subject so I always go to crucial's website as well as others and enter in the computer model and see what they recommend. If they all concur then I know I'm on the right track. To be even more sure, I'll visit this forum and ask. There are plenty of folks on this site that have near expert knowledge on the subject.

[I Use Dial]

And don't forget about the ThinkWiki!

[sjthinkpader]

There is no reason why a 512MB module of this type doesn't work. The only anomaly is that this module use TSOP chip packages that 16 chips doesn't fit a SODIMM board size. So they use a 2nd substrate then bond it and the main substrate together. Kentron calls it FEMMA.

Other manufacturers normally use BGA to mount 16 chips on a single substrate. Kentron's approach necessitate longer PWB trace length which can contribute to poorer signal quality.

[mike-s]

And don't forget about the ThinkWiki!

First place i went, had NOTHING on this kind of thing.

There is no reason why a 512MB module of this type doesn't work. The only anomaly is that this module use TSOP chip packages that 16 chips doesn't fit a SODIMM board size. So they use a 2nd substrate then bond it and the main substrate together. Kentron calls it FEMMA.

Other manufacturers normally use BGA to mount 16 chips on a single substrate. Kentron's approach necessitate longer PWB trace length which can contribute to poorer signal quality.

for what it's worth, this is the ram i purchased. Markings on the chips are as follows

32X16SDRAM WT
Q824
And there are 4 per side, in a dual sided configuration.

What leads me to believe i may have incompatible ram is that there is reference to * x 64 within the IBM memory guide. In any case i have contacted the guys i bought the ram off and have given them all the details and they are looking into the next appropriate action.


[CLARIFICATION] i realise i put in a link to Kentron, however that is not the ram i used. I was looking at different memory companies to see what sort of memory arrangements are available and what they class it as. I only linked to kentron only as they referred to the * x 64 arrangement as "high density" whereas the arrangement within the ram i purchses was 32X16. Apologies i didn't make it clearer when i put my initial post up, but it was rather late at night and i was on a nightshift and the obvious evidently totally eluded me. I have included a link to the ebay auction so you can see exactly what i purchased.

[sjthinkpader]

PC RAM are either x4, x8 or x16bits wide. Very few are x32bits. None are x64bits. The DDR SODIMM are organized as x64bits or 8 bytes wide.

This module appear to use 32Mx16 each chip x4 chips x2 banks; which is pretty normal.

A high density version would have used 64Mx8 each chip x8 chips x1 bank.

[mike-s]

A slight misscommunication between the tech dept and myself. They advised that they looked into my laptops requirements and the ram should have worked. I immediately got a RMA approved and sent the ram back this morning.

They are going to send me new memory (that they will check manually to ensure it works) and im just going to cross my fingers and hope. If it doesn't work i'll just swallow my pride and buy more ram from a local supplier and fling this stuff on ebay (or here perhaps) so that some other sod with a less picky laptop can get a relatively cheap upgrade.

funny enough the cost of sending the RMA back registered post cost exactly one third of what i paid for the ram, including postage!!