Hi, I have a HP DV9700 laptop that I bought about 1 and half year ago. The RAMS need to be replaced, and what's the maximum RAM speed (The Mhz, not the amount of GB) can I use in this laptop?

The old one was PC5300 667 Mhz 2 x 2GB RAM

Can I use PC6400 RAM?
because It's more easily available than the old PC5300.

You can try, good case is that the memory would clock down to 667mhz and still run, worst case is that the comp will not boot.

Specs call for PC5300 as you already know. Hit and miss when trying to move up ram speed.

cheers ...

Really not so hit or miss. Only issue on enthusiast notebooks. And since an Asus C90? That didn't even like the correct RAM if not the right brand have not heard of many real issues.

JEDEC standards require the backward compatibility of all DDR/DDR2/DDR3 to meet the standards. So really not an issue and for the same reason other than systems using RAM running out of spec's mixing speed does not even cause issue. HP's are mainstream

For the newer members compatibility is within type not that you can mix DDR/DDR2/DDR3 because you can't.

OP if PC-6400 SO-DIMM's are cheaper buy them. Trust me.

They will down clock but will run fine.

Go to crucial.com and answer the questions.