Memory bandwidth tests... any real differences (PC4300 vs. PC7100)

[graysky]

Common sense tell you that higher memory bandwidth should mean faster results, right? I set out to put this thought to the test looking at just two different memory dividers on my o/c'ed Q6600 system. At a FSB of 333 MHz, the slowest and fastest dividers I could run are:

 

1:1 a.k.a. PC5300 (667 MHz)

3:5 a.k.a. PC8888 (1,111 MHz)

 

 

Just for reference, as they relate to DDR2 memory:

PC4300=533 MHz
PC5300=667 MHz
PC6400=800 MHz
PC7100=900 MHz
PC8000=1,000 MHz
PC8500=1,066 MHz
PC8888=1,111 MHz
PC10600=1,333 MHz

 

The highest divider is 1:2 aka PC10600 (1,333 MHz) and it just wasn't stable with my hardware @ 333 MHz.

 

All other BIOS settings were held constant:

FSB = 333.34 MHz and multiplier = 9.0 which gives an overall core rate of 3.0 GHz.

DRAM voltage was 2.25V and timings were 5-5-5-15-4-30-10-10-10-11.

 

You can think of memory bandwidth as the diameter (size) of your memory's pipe. Quite often, the pipe's diameter isn't the bottle neck for a modern Intel-based system; it is usually much larger than the information flow to/from the processor. Think of it this way, if you can only flush your toilet twice per minute, it doesn't matter if the drain pipe connecting your home to the sewer is 3 inches around, or 8 inches around, or 18 inches around: the rate limiting step in removing water from your home is the toilet flushing/recycling and the pull of gravity, not the size of your drain line. The same is true for memory bandwidth.

 

After seeing the data I generated on a quad core @ 3.0 GHz, I concluded that this toilet analogy is pretty true: the higher memory bandwidth gave more or less no appreciable difference for real world applications. Shocked? I was.

 

Further, I should point out that in order for my system to run stable in PC8888 mode @ a FSB of 333, I had to boost my NB vcore two notches and raise my ICH to the max (both of which the BIOS colored red meaning "high risk.") The increased voltage means more heat production, and greater power consumption -- not worth it for small gains realized in my opinion. Anyway, the test details and results are below if you want to read on.

 

 

Relevant test hardware:

 

Motherboard: Asus P5B-Deluxe (BIOS 1215)

CPU: Intel C2Q - Q6600 (B3 revision)

Memory: Ballistix DDR2-1066 (PC2-8500)

 

"Real-World" Application Based Tests

 

I chose the following apps: lameenc, x264, winrar, and the trial version of Photohop CS3. I ran these tests on a freshly installed Windows XP Pro SP2 machine.

 

Lame version 3.97

Edited October 31, 2007 by graysky

[Waco]

This is why I almost always advocate buying "cheap" memory. Enthusiast memory is nice if you are competing for crazy benchmark scores but in general you'll never see the difference on any newer platform.

 

It's nice to see numbers though, thanks for taking the time to show this to people.

[graysky]

Glad you found it useful.

[Verran]

Glad you found it useful.

I certainly did too! Everyone's always making a big deal about memory that'll clock stupid high, but it just doesn't seem that useful. In most cases, you could swap it out for a $50 pair and they'd never know the difference.

 

Nice info you've got here.

[romeo55]

It depends, when you start OCing you'll probably want DDR2 1000. For example, nrgs OC on his C2D at 468 gets pretty close.

 

 

A lot of people pass 500FSB, thus requiring better ram, at least if you want to run 1:1.

 

EDIT: and isn't PC2 7100 something like 8xx mhz, not 1111? PC2 8500 is 1066, and PC2 4300 is 533 as well...

[Waco]

A lot of people pass 500FSB, thus requiring better ram, at least if you want to run 1:1.

When 1:1 nets you nearly nothing and costs a hell of a lot more to pull off...I'll go with saving that money for a better video card or something.