Can anyone explain in layman's terms CAS latency?

JoshBrowne · 29 Jan 2011 at 01:16

What does it actually mean in terms of performance?

What're good timings and what're bad timings?

Why for example 9-9-9-24 - what do the 9s mean, and what does the 24 mean?

When someone refers to "tightening up the CAS timings", they are obviously doing it for a reason, but how does it translate to what the RAM is actually doing?

Thanks!

hansp · 29 Jan 2011 at 01:41

Nothing happens instantanously. When your ram module is given a command, it takes x number of cycles to complete. Those number describe how fast (or how slow) it can do those things.

HangTime · 29 Jan 2011 at 01:41

OK here goes, not really an explanation but hopefully tells you what you need to know:

Lower is better in terms of performance. Generally speaking there is a tradeoff between memory speed and timings. So for example (random made up numbers, don't take them too seriously) 7-7-7-21 @ 1600mhz may be comprable to 9-9-9-24 @ 1900mhz.

Different architecture behaves differently, but in my experience the real world performance gain from 'tight' vs 'loose' timings is around 10% max. So you want tight timings, but don't pay a hefty premium for it.

As for what the numbers mean, you can read about it here: http://en.wikipedia.org/wiki/Memory_timings

95thrifles · 29 Jan 2011 at 01:57

Havent read HangTimes link, but bear in mind anyone can write anything they want in wikipedia whether its accurate or not, theres a link here which is actually Anandtechs review of the Asus Rampage Formula mobo, but features an indepth discussion on memory, timings and its effects, just ignore the specifics to do with the actual board, the factual content is there, its an older board which uses DDR2 rather than DDR3 so the speeds are lower as are the timings but again the principles the same

JoshBrowne · 29 Jan 2011 at 09:07

Haha nice to see you back here 95Thrifles. Found your other reply this morning. Yeah, thanks for the link hangtime I'll definitely read it, but I also question bullsh*tipedia's accuracy.

1Day · 29 Jan 2011 at 09:29

http://www.anandtech.com/show/3851/...now-about-sdram-memory-but-were-afraid-to-ask

A good read and not too technical. Will explain what CAS is.

j.col · 29 Jan 2011 at 15:56

95thrifles said:
theres a link here which is actually Anandtechs review of the Asus Rampage Formula mobo, but features an indepth discussion on memory, timings and its effects, just ignore the specifics to do with the actual board, the factual content is there, its an older board which uses DDR2 rather than DDR3 so the speeds are lower as are the timings but again the principles the same

good link, i understood some of it, but then it went way over my head

also i am surprised there is not a sticky about the basics of ram, as i have asked questions in here before.
also there is a lot of threads about mixing different ram dimms together.

just a friendly hint, that you (95thrifles) or big wayne or setter or hangtime might consider as the ram FAQ hasnt been updated since 2006