If you take a stick of DDR ram thats CAS 2, with a RAS to CAS delay of 3 and a Precharge of 4, then that stick is rated as 2-3-4, correct? Then what am I missing here with the 4 digit ratings like 2-2-2-6?

I have always felt like i have a pretty good understanding on how the whole process works, but normal sdram never used a 4 digit quantifier, is it just a marketting thing or does the 4th digit actually mean something for DDR?

Sorry you have to hear a newbish question coming from one of your esteemed staff, but I'm pretty sure i'm not the only one that doesnt know

youre not alone....ive been trying to find that one out myself....

I think icpiper posted a nice explenation the other day (let me just find it)


EDIT
http://forums.pcapex.com/showthread....3315#post43311

more nice info
http://forums.pcapex.com/showthread....2997#post42997

ah ok, the RAS active time is the spec I was missing. I wonder why that has only been with the advent of DDR? has anyone seen an older sdram board that allowed for this setting?

I don't know that it is something new, it is possible that it was always a standard setting but never defiated so there was no need to allow control over it.

It is also possible that playing with the other settings quickly became pointless if you couldn't also change this one as well. It could have been sabotaging the tweeking of the others.

The other possibility is that it does primarily affect DDR because of the new aspects of that memory format.

Because SDRAM only sent data on the falling slope of the signal, it used the rising slop for timing. DDR uses the rising and falling slope, so they probably had to select a new "trigger" for timing and such. In effect, you might need a new setting.

I'll try and find out more.

Thanks LC