DDR2 533 vs. DDR2 800 RAM: Which is right for me?

RBach

So I'm considering a modest memory upgrade to my computer so that I might run several virtual machines simultaneously. This is mainly just for fun toying around, but that's beside the point. I have a variant of the Intel DG965SS and according to the documentation is supports up to 8GB of RAM. Sounds great, right? Well, there's a small problem in that it is somewhat fickle in what it supposedly will accept. The board supports 533, 667, and 800 MHz DDR2 RAM, but it will only run at 533 MHz or 667 MHz if you put 8GB of memory in there. I'm using 1.5GB of 533 MHz RAM now (2 512MB dimms and 2 256MB dimms). The board has 4 slots and I'me obviously going to have to toss two or four dimms out if I upgrade (depending on whether or not I get 4 or 8 GB). So, now on to my questions.

1) As I understand it, if I were to get 4GB of 800MHz RAM and mix it with some of that 533MHz memory, it will all run at 533MHz. Is this correct?
2) What would happen if I replaced all my current RAM with 8GB of 800MHz memory? My board apparently can't run that much memory at that speed, so what will happen? Will it not boot? Will it automatically run at 533MHz or 667MHz?
3) Suppose it automatically underclocks to 667MHz. Should I manually set it to 533MHz? The system FSB is running at 1066MHz (and I believe that's the board/processor's max) so wouldn't it be best to match the RAM to that speed?

I'd just get the 533MHz memory and not worry about things, but for some bizarre reason 800MHz memory seems to be cheaper than its slower counterpart on Newegg and I see no reason to spend more if I don't have to.

Thanks for your help, guys.

By the way, here's my exact board.

ArcSyn

What are the timings of the two brands of RAM you are looking at?

1) Yes, it runs at the slowest rated speed of the RAM installed.
2) It would most likely auto-clock to something it supported, like 667MHz when it booted.
3) Possibly, depending on the timings and processor, etc. It is probably one of those things where if you're looking for a few extra calcs per second you would want to do, but really you would never notice the difference.

If the 800MHz is cheaper, it's either because the timings (2-2-2-12 vs. 3-3-3-15 or something) are worse on the 800, or the 800 is mass produced so they've reduced the cost and therefore the price. (Similar to how DDR is more expensive than DDR2 now because DDR isn't mass produced as much)

RBach

Here is the 533MHz RAM I was looking at and the then there is the 800 MHz RAM. The 800MHz memory does indeed have a higher CAS latency than the 533MHz memory. Will 4 vs. 5 make that large ($14 worth) of a difference?

ArcSyn

RBach wrote: »

Here is the 533MHz RAM I was looking at and the then there is the 800 MHz RAM. The 800MHz memory does indeed have a higher CAS latency than the 533MHz memory. Will 4 vs. 5 make that large ($14 worth) of a difference?

The one you linked has a CAS of 6, but here's the basic gist of it:

It won't matter that it has a higher CAS because the higher frequency makes up for it. So you'll end up with the same speed. (The reason I asked is if it was drastically different, like CAS2/3 vs. CAS8 or something ridiculous) If it drops the frequency, you can check (and possibly manually change if it doesn't automatically) to make sure the timings are adjusted accordingly as well to keep the latency the same.

Detailed overview if you wish to hurt your brain

From the chart posted here, DDR2 533MHz at CAS4 is roughly = to DDR2 800MHz at CAS6.

If you were to put in 8GB and slow it down to 667MHz, the CAS should change from CAS6 to CAS5 to compensate.

tl:dr - Get the cheaper stuff

RBach

ArcSyn wrote: »

tl:dr - Get the cheaper stuff

Can do!

Thanks.