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I've already got 1 gig of ram. If I buy two sticks @1 gig each, can I add them?

Or do I need 2,4,8, etc. Will 3 work or will it only count 2?

Also, can I mix DDR2 and DDR3 RAM?

I have a Dell Dimension E521

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up vote 3 down vote accepted

According to Dell's product page on the Dimension E521, you can upgrade up to a maximum of 4GB.

The service manual shows you have four DIMM slots, so you can install an additional pair of 1GB sticks. I doubt your system has four 256MB modules in it, so you shouldn't have to remove anything. You probably currently have either one 1GB module, or two 512MB modules.

To answer the second part of your question, no, you cannot mix DDR2 and DDR3. Your computer only supports DDR2, so make sure you purchase the right type. According to Wikipedia:

DDR3 SDRAM is an improvement over its predecessor, DDR2 SDRAM, and the two are not compatible.

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But can I just put 3 or do I have to do 4? – Citizen May 31 '10 at 5:28
I must have missed the important bit of your question there, sorry. I found the service manual and added findings to my answer. – Stephen Jennings May 31 '10 at 8:00

This has nothing to do with the operating system. You will need to read the motherboard manual in order to discover what combinations may be supported.

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Which question are you referring to? I'm on a Dell Dimension E521 – Citizen May 31 '10 at 5:17
A​ll o​f them​. – Ignacio Vazquez-Abrams May 31 '10 at 5:35

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