X201, I think from about 2010 or 2011. It's a little slow, but with the ssd, 8gb ram (instead of 4) and running Linux Mint, it sure isn't bad for a 10+
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OFFTEK 4GB Replacement Memory RAM Upgrade for IBM-Lenovo ThinkPad X201 (All Types) (DDR3-8500) Laptop Memory at Amazon.com