Ok, I've a question. I was in contact with Crucial....

[FIRSTJONTAR]

This morning for this reason:
I just purchased a T20 and I've been searching high and low for a decent price on 256mb memory cards. That is how I stumbled across this fantastic site. Reading the sticky regarding memory and how pc133 will actually work in this laptop, etc.

the link for the T23 chip:

http://www.crucial.com/store/listparts. ... &submit=go

And the link for the T20 chip:
http://www.crucial.com/store/listparts. ... &submit=go

the units appear to be similar. Hence me contacting Crucial, and the "On-line Chat" person said the difference was the refresh rate was faster on the T20 chipset.
The question I pose is this.. does it make a difference?

[rkawakami]

Welcome to thinkpads.com!

The T20 originally was provided with PC100 (100Mhz) memory. In the ensuing years, PC133 (133Mhz) has replaced it. You CAN use the faster PC133 module inside the T20 as long as you make sure that it is of the "low density" variety (as opposed to the "high density" versions). How can you tell which is which?

For a 256MB module, the low density version will have a total of 16 memory "chips" on the board (usually 8 per side). A 256MB module that has only 8 chips is a high density version and will not work in the T20. The Crucial apps person had it somewhat correct that the "refresh rate" is different between the two. The real difference is that the T20 chipset requires the use of memory that has a 4096 refresh cycle specification, whereas the T23 chipset generates 8192 cycles. This means that you can plug in a low OR high density module into a T23, but the T20 can ONLY use a low density version.

Low density 256MB modules can be sourced from eBay anywhere from $15 to $50 depending upon how lucky, patient and/or desperate you are.

edit: You can find them by the IBM part numbers (33L3069 or 33L3070), but as pointed out before, those auctions tend to have higher closing prices than a generic 256MB PC100 listing for a Dell or an HP system, for example.