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RAM 101 HELP!

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February 25, 2011 10:44:34 PM

I'm confused about DDRs and PC#-####s in regards to compatibility. Can I install DDR2 modules on boards with DDR3 modules and vice-versa? Can I install PC2-5300 modules on boards with PC2-8500 modules and vice-versa? Finally, can I put PC3 modules on boards with PC2 modules and vice-versa?

For example: If my laptop uses a PC3-8500 RAM can I install a PC2-5300 module on it? If I have a module how can I tell what machines will it work with? Likewise, if I know the RAM that is installed on my machine, how can I determine what other RAMs will work on it? Crucial.com has a good compatibility check feature but I'd like to understand the concept in general rather than having to go to the site each time.

More about : ram 101

a b } Memory
February 26, 2011 12:29:35 AM

This topic has been moved from the section Storage to section Motherboards & Memory by Tecmo34
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a b } Memory
February 26, 2011 1:05:06 AM

DDR2 and DDR3 RAM have different physical connectors. They cannot be interchanged, unless the board is specially designed to have both types of slots. Even then, you cannot use both types at the same time.

You can put different speeds of the same type of memory in the board, but the faster memory will run at the speed of the slower memory.
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February 26, 2011 5:01:51 AM

Thank you for the reply Leaps-from-Shadows. So now I know that I cannot interchange between DDR2 and DDR3 and that I can upgrade to a faster speed, but only the lower speed will be used if I have two different speeds running at the same time. But how about between the PC2 and PC3's? Can I use a PC2 on a PC3 and vice-versa?
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a b } Memory
February 26, 2011 5:38:27 AM

PC2 = DDR2
PC3 = DDR3

So, the answer is ... no.
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February 26, 2011 6:32:58 AM

Great. That was easy. So it's really just a matter of speed then. THANK YOU Leaps-from-Shadows!
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February 27, 2011 6:21:28 AM

Leaps-from-Shadows said:
DDR2 and DDR3 RAM have different physical connectors. They cannot be interchanged, unless the board is specially designed to have both types of slots. Even then, you cannot use both types at the same time.

You can put different speeds of the same type of memory in the board, but the faster memory will run at the speed of the slower memory.


not sure this is 100% correct. ddr2 and ddr3 both come in form factor 204pin sodimm (and others).

my hp 100z only has two mem slots and is ddr2 and ddr3 compatible.

with boards that have mem controller that interleaves (most if not all chips today) say 2/4/6 slots it may be possible to run ddr2 in one channel and ddr3 in the other, likely depends on the memory controller. but is it the norm to use the same type and speed ram.
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a b } Memory
February 27, 2011 1:45:12 PM

You cannot use both types at the same time. If you've read that somewhere, it was wrong.

The "key" slot is in different positions on DDR2 and DDR3, so despite the fact that they have the same number of pins (240), they cannot be interchanged.

I looked at the site for your HP computer. That's likely a typo on their part. I know for a fact that normal 240-pin DDR2 and DDR3 DIMMs cannot be interchanged.

Edit: DDR2 SO-DIMMs are 200-pin, and DDR3 SO-DIMMs are 204-pin. They also cannot be interchanged.
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March 9, 2011 7:32:49 AM

Best answer selected by medyo.
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