my type of RAM ...

I have a thinkCenter Lenovo tower at work which memory I would like
upgrade with one more gig
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the box' manual says it should be one of the types 8288, 8297, 8326,
8329, 8342, 8380
;-)
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I read in there I should use 1.8V, 240-pin DDR2 SDRAM, but I don't
know if they should be:
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1.) FULLY BUFFERED, REGISTERED or UNBUFFERED
2.) ECC or non ECC
3.) DDR2-533, DDR2-677 or DDR2-800
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The type of RAM you use is very important and I don't want to create
any problems with the box itself
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http://www.crucial.com/ or one of these sites used to have a page
that would narrow down the options for you once you gave your type of
computer
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how can you know for absolutely sure the type of computer you need?
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thanx
lbrtchx