Originally Posted by
number_6
Intel added the capability for newer chipsets (starting with 945GM, I think) to control this and some drivers implement a lower power memory refresh. Quite significant (I know some Vista drivers have it, and Linux is working on it but don't think it is released yet, don't think Mac has it yet). If you are interested in this significant new technology, see the intel site and look for things like Memory Row Power Management (DRPM) and Conditional Memory Self-Refresh (CMSR).
Otherwise your comments are 100% correct for the older chipsets and memory controllers; but no current T series Thinkpad uses that technology any more -- and does benefit from longer battery life even with 4GB memory. The hardware came circa 2006, the software a year later (and few people realize it, apparently).
Yes, these came from the low power DRAM designs originally used in cellphones now making it into PC memory. Starting point is the JEDEC (Joint Electron Device Engineering Council) JC42 committees for memory standards.
http://www.jedec.org/memory_program/program.htm
I suspect my T60 still don't have it. Frankly I expected more battery life from my machine. Although I have the big battery, I really hate to carry it on a trip. The X60s' some colleagues have are great on battery life but they have a tiny screen. For our work, we typically only use 1GB of RAM and I've only recently gone to 2GB.
RAM usage bit growth had not been increasing as rapidly as in the past. So the RAM pricing is in the dump this fall. Now you can buy 1GB for about $20. Order the single SODIMM option in any case to leave one empty slot for adding RAM in the future.