Question about dual channel ram.

Energize · 2 Jul 2006 at 01:55

I was wondering what having dual channel ram actually does to things like memory speed and such. Since people are always saying run ram in dual channel mode.

Defcon5 · 2 Jul 2006 at 09:52

Do you mean memory speed as in the DDR frequency it runs at or the latencies?

Whan running in dual channel its possible that you will have to use a slightly lower freq. but this loss is more than made up for by the benifits of dual channel

Dual channel itself is where the memory and cpu/nb can communicate with each other at the same time rather than cpu -> mem then mem -> cpu.

I think it enables info to be sent on the rise and fall of each clock cycle

Minstadave · 2 Jul 2006 at 10:31

Running dual channel means that the two memory modules are being accessed by seperate memory controller channels, theoretically doubling memory bandwidth, it doesn't affect timings or latencies. The best image I can think of is its like turning a single lane road into a dual carriage way, the cars all travel at the same speed, but now you have two lanes, twice as many cars can get from A to B.

In real world terms you see about a 2-3% increase in gaming performance on Socket A and a 10% ish performance increase on A64 when using dual channel over single channel.

Energize · 2 Jul 2006 at 15:48

So would 2 400mhz sticks be equal to 1 800mhz stick then?

Minstadave · 2 Jul 2006 at 16:06

Energize said:
So would 2 400mhz sticks be equal to 1 800mhz stick then?

Theoretically yes, you could have a single 512mb module in single channel and 2x256mb modules in dual channel. The latter solution should give twice the bandwidth, and this can be seen using synthetic tests such as SiSoft. On socket A it is far less noticeable, but A64 shows the bandwidth increase in SiSoft very noticably.

For real word apps the increase in bandwidth has a small to moderate effect on performance.

Energize · 2 Jul 2006 at 16:39

Then whats the point in ddr2 800mhz sticks?

Minstadave · 2 Jul 2006 at 16:41

Energize said:
Then whats the point in ddr2 800mhz sticks?

Because you put them in dual channel too for massive bandwidth :confused:

Dual channel DDR2 800Mhz > Dual channel DDR 400Mhz

Energize · 2 Jul 2006 at 16:43

But cpus cant utilize all that can they? I thought amd 64 cpus only had a 1000mhz htt. Unless you can overclock the fsb by 60%?

Minstadave · 2 Jul 2006 at 16:45

Energize said:
But cpus cant utilize all that can they? I thought amd 64 cpus only had a 1000mhz htt.

AM2 CPUs don't really need the bandwidth of DDR2 anyway, its Conroe that seems to benefit, it allows for massive 1:1 overclocks:

http://forums.overclockers.co.uk/showpost.php?p=7328818&postcount=1

Energize · 2 Jul 2006 at 20:27

Why did everything switch to ddr 2 surely they could have made faster ddr ram? They already had 625Mhz ddr ram didnt they and now you need new ram when you want to upgrade.

james.miller · 2 Jul 2006 at 20:35

ddr2 is cheaper to produce, apparently.

Energize · 2 Jul 2006 at 20:44

Looking at the prices ddr2 is much more expensive than the equivilent ddr.

james.miller · 2 Jul 2006 at 20:46

yes i know that. i said it was cheaper to produce

Energize · 2 Jul 2006 at 20:47

Does ddr2 clock any better than ddr?

james.miller · 2 Jul 2006 at 21:19

massively. corsair xms2-8500 for example is varified to run at 1066mhz. dd2 has the potential to be much faster, but atm its at the expense of timings.

Minstadave · 2 Jul 2006 at 21:34

Energize said:
Why did everything switch to ddr 2 surely they could have made faster ddr ram? They already had 625Mhz ddr ram didnt they and now you need new ram when you want to upgrade.

DDR2 had already started to mature on graphics card (is GDDR2 the same as DDR2 anyone? I'm not actually sure) and it was probably far more economical to switch to DDR2 than keep pushing DDR1.

Energize · 2 Jul 2006 at 21:38

So because the memory timings are slower are the am2 systems at stock are slower than the equivilent 939 systems?

Mikey1280 · 2 Jul 2006 at 22:04

Energize said:
So because the memory timings are slower are the am2 systems at stock are slower than the equivilent 939 systems?

Nope because while the timings are slacker the frequency is higher. AM2 rigs are slightly faster than 939 rigs, not by much though.

Minstadave · 2 Jul 2006 at 22:07

Mikey1280 said:
Nope because while the timings are slacker the frequency is higher. AM2 rigs are slightly faster than 939 rigs, not by much though.

Yeah a 1-2% boost at most really. S939 was never limited by bandwidth, so adding more with DDR2 is going to minor gains with current gen processors.

Energize · 3 Jul 2006 at 00:01

Oh and another question does more ram = possibly more latency because the pc has to search a larger amount of ram to find the data needed?