View Full Version : Memory speeds versus rating

10-09-02, 04:27 PM
This may sound like a dumb question to you video card experts, but:

On every card Ive owned (GF2s, 3s, 4), the memory was clocked significantly slower than its actual rating. Why is this?

For example, if my GF4 TI4600 has 2.8 ns DDR=714 MHz (approximately), why does it come factory-clocked at 650?

Ive heard its for stability reasons, but isnt that exactly what the rating means? So if its rated to run at 714 MHz, why would it be unstable at that frequency?

2nd part of the question is: assuming above is true, is it really considered "overclocking" for me to to push that slider to 700 MHz? What possible risk do I run by setting the frequency to its actual rated speed?

Bigus Dickus
10-09-02, 04:49 PM
I'll offer one possible explanation: have you ever encountered the effect of a system scoring higher on tests with its system ram running at 133MHz Cas2 vs. 140MHz Cas3? The same could well be true on video cards... that is, manufacturers could have aggressive memory timings that have a better overall performance than a combination of less agressive timings and higher memory clock speeds.

And combined with the explanation that it is for stability reasons (that, with the agressive settings, they aren't comfortable running the memory at its maximum rated speed), I that probably covers it.

I could be entirely wrong though... perhaps they just don't like numbers like 714? :D

10-09-02, 04:57 PM
Yeah, 714 is an awkward number. But 700 would put the card at just under its rated speed, thereby helping stability as well as making the card a bit faster.

And yes, I see what youre saying about the memory; a friend and I have almost same systems, except that I have DDR 266 and he has 333. However, mine tests better because I run mine at 2-2-2-5 (Crucial), whereas he cannot (bargain-bin crap).

10-09-02, 05:50 PM
i would say, incrementally overclock your memory and do extensive testing. then stick with whatever is the highest setting that you can keep the card running stable at.

also, when evaluating information from other threads, it seems like even though video memory is rated at a certain speed, not all memory can actually achieve that speed. so that could be due to several different factors like: immature process, "cheap" high end memory, or aggressive timings that destabilize at higher frequencies.

for example, supposedly many early GF3 users couldn't overclock their memory that much, but GF3Ti500 users(which used memory of the same spec) could overclock further, and indeed the memory was clocked higher at default than the original GF3's memory was.