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CMS 8GB (2X4GB) DDR3 8500 1066MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Lenovo® Thinkpad T400 2764, 2765, 2766, 2767, 2768 - A35 at Amazon.com
Tutorial: How to Upgrade T410/T420/400 Thinkpad Laptop to 8GB - YouTube
Used Lenovo ThinkPad T400 Notebook - Core 2 Duo 2.40GHz - 4GB DDR3 - 160GB - DVDRW - Windows 7 Pro 64bit - Walmart.com