4GB 2X2GB RAM Memory for Lenovo ThinkPad X Series X61 (76734NU) Black Diamond Memory Module DDR2 SO-DIMM 200pin PC2-4200 533MHz Upgrade System Specific Memory - Newegg.com
How to upgrade the RAM and SSD on the Lenovo ThinkPad X1 Extreme
2GB Memory RAM Upgrade for the Lenovo Thinkpad R61 Series, T60 Series, T61 Series, X60 Series and X61 Series Laptops (DDR2-667, PC2-5300, SODIMM) at Amazon.com
2GB RAM Memory for Lenovo ThinkPad X61 Tablet Black Diamond Memory Module DDR2 SO-DIMM 200pin PC2-5300 667MHz Upgrade System Specific Memory - Newegg.com
Slow Computer? Don't Replace, Revive! – Y42K.com – Ray Charbonneau
Upgrading the CPU in ThinkPad X61 — Wenting's Web Page