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I have an old notebook which I use from time to time and would like to upgrade its RAM since it's really slow... It has two slots and only one is used, so I want to buy another RAM to put into the other slot.

Right now, the notebook has 1 x DDR2 PC2-4200 533MHz 512MB.

I have 2 options for the second slot:

a) DDR2 PC2-4200 533MHz 1024MB
b) DDR2 PC2-5400 667MHz 1024MB

Which one should I choose, so that the performance of the notebook will be the best possible?
If I mix two RAMs with different speeds, is the RAM with the higher speed gonna operate at a lower speed of the other RAM?

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closed as off topic by Brad Patton, Simon, 8088, Joe Taylor, laurent Apr 24 '13 at 19:01

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up vote 1 down vote accepted

Whenever you put in RAM that have different speeds, the lowest one will set the "standard" for the other memories. In your case, even if you put in the 667MHz ran, it will perform at 533MHz.

Is there any reason why you don't put in both a and b and remove the 512MB of RAM?

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the 512 could be soldered on? – surfasb Jan 1 '12 at 11:16
I've seen that on much much older laptops but not ones that supported 2gb Max. Interesting. – kobaltz Jan 1 '12 at 15:39
Or really small laptops. My Dell XT2 has 1GB soldered, and one slot free. – surfasb Jan 2 '12 at 0:10

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