When I upgraded my RAM quite a while back I told the shop keeper that I wanted to buy 4 2Gb RAM sticks.
He made some phone call and couple minutes later they came up with 3 Kingston memory stick made in Malaysia and another 1 Kingston memory stick made in China. All four are supposed to have the same spec but when I looked at the circuit board you can see quite a lot of differences in layout.
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I've no big problems aside from weeks a year of windows crashes but not sure what's causing those.