Could someone quickly explain DDR2 Ocing values?

keogh · 6 Apr 2007 at 21:28

Howdy,

I understand most things bout overclocking... but I am still a bit confused on one with with clocking RAM?

I understand timings, thats all good... but the actual clock speed I don't get?

For example, my last PC took DDR PC3200 and was labelled as 400mhz. But when I was clocking it I had to keep its around 200mhz... I had it as 220mhz. So what I am confused about is all these numbers? 3200, 400mhz... so where does the 200mhz come from? Why wasn't I suppose to clock it to 400mhz+ opposed to 200mhz+?

Was it cos I had 2 sticks, so 2x 200=400mhz? Or is it some maths where you basically have to half it?

My new PC has GeIL 2GB (2x1GB) PC6400C4 800MHz Ultra Low Latency DDR2 Dual Channel Kit (GX22GB6400UDC) so I assume I would have to keep this to 400mhz+ right? Or do I have to clock this to 800mhz?

Please help me with this cos I am confused?

also whilst I'm here, if I say got my timings to 4-4-4-12 1T and got that stable at the stock mhz speed... would that mean that those timings would run fine with any stable clock speed? I'm asking cos I would set my timings up first, once I have those stable I would then start clocking the speed of the ram... if it dies would I know its the speed change/DDR volt that is killing it? Or could it be that the DDR will run fine at that speed, just it doesnt like those timings at that speed? Does that make sense?

Please explain anything you can about RAM overclocking... I need help!

thanks

w3bbo · 6 Apr 2007 at 22:04

The data transfer rate for DDR RAM is twice the memory clock speed because it performs two data transfers per clock. For DDR2 it is four times the memory clock speed because it transfers twice the data during the same clock cycle as standard DDR.
e.g

DDR2-400 = 100 MHz(memory clockspeed) 200 MHz (Memory data bus speed)
DDR2-800 = 200 MHz(memory clockspeed) 400 MHz(Memory data bus speed)

You have yours set correctly (400) which in effect is 200x4 =800mhz - confusing I know.

So...

PC6400 = bandwidth
800mhz advertised is 200mhz memory clockspeed x 4 (as its ddr2) = 800mhz

Hope you can follow that

keogh · 6 Apr 2007 at 22:22

Wow that is a lot to take in... why make it so confusing huh

I understand it though... so my PC6400 in my PC now I should keep around 400mhz, and see if I can clock that up by 10mhz above 400... id that makes sense?

What about my question on the timings and speeds? Do tighter timings not work with higher bus speeds? Or would timings work at any STABLE bus speed on the RAM... if you know what I mean?

Thanks w3bbo, appreciate your help!

w3bbo · 9 Apr 2007 at 07:53

keogh said:
Wow that is a lot to take in... why make it so confusing huh

I understand it though... so my PC6400 in my PC now I should keep around 400mhz, and see if I can clock that up by 10mhz above 400... id that makes sense?

What about my question on the timings and speeds? Do tighter timings not work with higher bus speeds? Or would timings work at any STABLE bus speed on the RAM... if you know what I mean?

Thanks w3bbo, appreciate your help!

It is all RAM dependent m8, there are no set rules on how far memory will overclock just as there are none for cpu's. Buying the best overclocking memory available will obviously help and at the minute these are modules with Micron D9 chips (Cellshock/TeamXtreme/GSkill HZ). Getting these modules to 500(1000)mhz seems entirely possible going by a lot of folks results and at tight timings aswell.

Your Geil sticks sadly are not the best when overclocking. They are not bad by any stretch of the imagination but don't expect them to clock as good as the ones above.

To answer your Q: The faster the bus speed over stock the slacker you will most likely have to put your ram e.g if you have your memory running at 50mhz(100) over stock such as 900mhz then you may have to slacken your timings to 5-5-5-15. CAS is generally considered the one to change first as it is the one that has the most effect so try 5-4-4-12 and run a memory benchmark such as memtest or superPI. If it fails then raise the other values one at a time. If you put your memory on a divider and thus keep it around the stock 400(800)mhz mark then you can keep the timings at stock to (4-4-4-12) or maybe even tighten them (4-3-3-8).

As always you should run benchmarks of your favourite programs to see what effect the memory overclock has on them as some programs benefit from higher bandwidth/slack timings and others prefer nominal bandwidth with tight timings. Ideally you want to find a middle ground. Overcloking memory is much harder than CPU as there are a lot more variables to contend with.

Good luck