PC vs. PC2 memory

[moot]

I've looked around and don't see what the difference is.
I only need to know what the difference is, or a link to something explaining it, but here's the context:

I'm building a cheap temporary box:
AMD64 X2 3600
ASUS M2A-VM
Kingston 1GB PC2 5300 DDR2

Does the ram have to be PC2, or can it be PC?

Thanks!

[NHawk]

In simple terms, the difference is in the speed, number of pins on the module and the way the memory is addressed. And YES the memory for that board must be PC2

And speaking of memory speed, why pair slow DDR2-667 (PC2-5300) memory on a board that supports faster DDR2-800(PC2-6400)?

[moot]

I guess I'm just cheap.. I have to stretch my expenses a lot for a moment, and 200 bucks is my budget for this thing.  Performance doesn't matter so much as finding the best parts within budget, so if you've got suggestions, I'm all ears.

Thanks again

[Skuzzy]

Thre is DDR1, DDR2, and soon, DDR3.  None of which are compatible with the other.  They are based on different silicon designs.  Each has its own positives and negatives.

Although DDR3 looks more promising than any previous RAM technology as it takes the best of DDR1 and DDR2 and combines it, while getting rid of the negatives of DDR1 and DDR2.

[NHawk]

Originally posted by moot
I guess I'm just cheap.. I have to stretch my expenses a lot for a moment, and 200 bucks is my budget for this thing.  Performance doesn't matter so much as finding the best parts within budget, so if you've got suggestions, I'm all ears.

Thanks again

It depends on how tight the budget is. The board and CPU run about $129. You can get a decent 2 Gigs of PC800 memory for between $79 and $109.

[Fulmar]

Originally posted by NHawk
And speaking of memory speed, why pair slow DDR2-667 (PC2-5300) memory on a board that supports faster DDR2-800(PC2-6400)?

Depends on FSB of the CPU.  I can't remember what it is off the top of my head for AMD processors.  Ideally you'll want to keep the FSB and DDR speed at a 1:1 ratio.  You can google for benchmarks on 533mhz vs 667 and you'll see nominal difference in benchmarks, even at the 800mhz level.  (So, if you FSB is 1066mhz, you want 533mhz to match it equally because you are using DDR2, thus double the mhz speed of the ramto formulate the ratio, in this case 1066FSB=667x2 Ram).  The benefit to say having a higher DDR speed than the FSB is overclocking.  You'd be able to set the FSB of the CPU faster to match a 1:1 ratio with the Ram.

Also with faster Ram you can upgrade if need be w/o having your ram suffer on your CPU.  Example.  My computer is a Intel E6400 (1066mhz FSB).  I use 667mhz Ram for two reasons.  My board supports quad core which I plan on upgrading to in the future.  Quad core Intels run at 1333mhz.  Thus when I upgrade my Ram will not be slowing down my computer (667mhz DDR2 ~ 1333mhz).  As of right now I also have my FSB at 1333mhz, CPU speed is upped to 2.66ghz (from 2.13 or something).

[Fulmar]

As of right now, Ram prices are dropping really fast.  I paid $220+ for my 2gb of 667mhz DDR2 back in January.  Now that same ram is around $130 last time I checked.  It doesn't hurt to spend the few extra bucks (if you're not on a serious budget crunch) to get the faster ram.  This will let you upgrade in the future w/o buying new ram.  However if you just buy new computers from scratch and do not upgrade, then ignore that and buy the Ram that matches a 1:1 ratio with your CPU FSB.

LOOK FOR GOOD MEMORY TIMINGS.  Like 4-4-4-12 is good.  5-5-5-15 is bad.

Also warranty is good as well.  Look for Lifetime warranties and avoid off name brands.

[NHawk]

Umm... Unless I'm totally mis-reading your post I have to disagree with your equations.

DDR2-667 memory RUNS at 333Mhz, not 667. DDR stands for Double Data Rate. The memory runs at 333Mhz but transfers data at 667Mhz.

Just as DDR2-800 runs at 400Mhz but transfers data at 800Mhz.

With that info to even come close to equaling the 1066Mhz FSB you'd need DDR2-2132 (which doesn't exist) to RUN at the same speed as the FSB or DDR2-1066 to transfer data at the same rate of the FSB.

[Kermit de frog]

NHawk, read fulmar again.  Your last sentence false.

Yes DDR2-800 does run at 400MHz on each side of the stick, therefore it gets an equivalent transfer speed 800MHz as a whole.  That 1 stick of memory is capable of transfering info at 800MHz.

If you get 2 sticks and run them in dual channel, you get an effective speed of 1600MHz.

So, DDR2-533 in dual channel mode gives you an effective speed of 1066MHz, giving you a 1:1 ratio for your FSB to Memory speed.

I just repeated what fulmar said.  

[NHawk]

I saw nothing in his post about Dual Channelling.

In that case, I'd much rather have the memory waiting on the FSB than matching the FSB or having the FSB wait for the memory.

I run DDR2-800 Dual Channel memory on a 1066 FSB.

[Krusty]

Dual channel does not double the speed at which the info is trasfered to and from the RAM. It only gives you a total system boost of 15% or less.

Has to do with reducing the number of cycles that "wait" while writing/reading to the module, if I recall. Doesn't enhance the speed of the ram itself, just reduces the time that ram sits around waiting for the next free cycle.

EDIT: P.S. A lot of newer motherboards have separate frequencies for PCI busses, CPU busses, and probably for RAM busses, so it doesn't really help to have a 1:1 ratio if that is totally coincidental and provides no benefit.

[Fulmar]

Sorry, I was wrong about my facts.  I kind of mixed it up.

Yes, DDR2 at 667mhz is actually 333mhz.  The Intel C2D's use Quad-pumped FSB's.  So 1066 is actually 266mhz, thus 533mhz DDR2 is the correct match for it.

Thanks for bringing it to my attention, my logic was reversed on it.  However, the idea of maintaing a 1:1 ratio is still correct.

Dual channel does not double the speed, dual channel in lehman's terms roughly gives you about a 15% performance increase in the memory department.

[Fulmar]

Originally posted by Krusty
EDIT: P.S. A lot of newer motherboards have separate frequencies for PCI busses, CPU busses, and probably for RAM busses, so it doesn't really help to have a 1:1 ratio if that is totally coincidental and provides no benefit.

This is true, but they are all not on the same 'channel.'  The Memory goes directly to the CPU with data.  It has its own separate channel than the PCI channel.  Memory and PCI and all the other info do not travel on the same channel to the CPU.

By maintaing a 1:1 ratio you are fully utilizing the bandwidth on the channel from the memory to the CPU.  Say the memory is faster and the ratio is 4:5, the CPU is not the bottleneck for the system, and vise versa.  That's why 667mhz DDR2 will not see any major performance difference between its 533mhz brother when the CPU FSB is 1066FSB.

[Kermit de frog]

Due to the timing, it's best to achieve a 1:1 or 1:2 ratio.  You may not get an improvement with a 4:5 ratio or 3:5 ratio.  Underclocking memory can be a good thing.  As a general rule, you don't want to under clock by a huge margin of it's rated speed.

Underclocking can also allow lower voltages to be used and therefore help keep it cooler and in effect, help it's lifespan extend.

People think that having the memory alittle bit faster than the CPU would mean less "wait" states for the cpu, when infact it can increase "wait" states because of timing issues.  I can't prove this myself, but will look for document that I can bring to this forum to show to others.  My college books are of no use because they don't cover Duo Core Processors .  In the mean time, just search for the hundreds of benchmarks on the web.

NHawk, I see that fulmar was talking about 2 ram sticks, which he was thinking dual channel, but he never did specifically say dual channel.  I see your point.

Oh and as always, results vary from PC to PC.