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Latency question

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  • Memory
  • DDR2
  • Latency
Last response: in Memory
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August 13, 2006 1:25:10 AM

For DDR2 800, is 5 5 5 12 a good latency? Is higher better, or lower? I read the sticky and it gave the definition, but I did not see anything else about it. (Ok, so I browsed the sticky).

More about : latency question

August 13, 2006 1:55:57 AM

In numbering, 5-5-5-12, the first 5 refers to the CAS latency. The lower this number is, the better for speed. If you want a fast DDR2, look for a CAS of 3, or 4 at the worst.
August 13, 2006 2:05:19 AM

Thanks...but what about the next 3 numbers? Lower is better with them, too?
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August 13, 2006 2:43:27 AM

Quote:
Thanks...but what about the next 3 numbers? Lower is better with them, too?

For all numbers (5-5-5-12), lower is better.
August 13, 2006 3:00:23 AM

Quote:
Lower is better with them, too?

Yes. The DDR2-800 is really popular because of Socket AM2, and regular CAS5 stuff is pretty affordable (less in some cases than 2GB of DDR). CAS4 stuff is another $50 bucks. But CAS3 @ 800MHz will cost you big.
Note: Just about any PC2-6400 (800MHz) memory is CAS3 at a lower speed. For example, running a Conroe using 1:1 FSB:RAM (synchronous) gives a memory speed of 533MHz (which is PC4200 speed). This in dual-channel perfectly matches the CPU's 8.4 GB/s bandwidth. In theory, more memory bandwidth shouldn't be any faster, and there is also a latency (or time delay) introduced because of asynchronous operation.
So I am running my CAS4 OCZ @ 533MHz with very tight CAS3 timings.
Now, the Athlon guys can run a full 1:2 ratio - at which point the enormous bandwidth makes a little asynchronous latency nothing to worry about.
As a new Intel Guy (still an AMD guy also) but as an Intel guy I say, Show me PC2-8400 @ 1066MHz! Then I too will run 1:2 ratio.
But that stuff costs BIG, even CAS5...
Regards
August 13, 2006 3:27:29 AM

Latency is always better lower, and Freqeuncy is better higher.


And a bit off-topic:
Quote:
As a new Intel Guy (still an AMD guy also) but as an Intel guy I say, Show me PC2-8400 @ 1066MHz! Then I too will run 1:2 ratio.
But that stuff costs BIG, even CAS5...
Regards


Doing that, BW is about 14GB/s (78%) in the sandra buffered test. :p 
August 13, 2006 1:08:17 PM

Quote:
Lower is better with them, too?

Yes. The DDR2-800 is really popular because of Socket AM2, and regular CAS5 stuff is pretty affordable (less in some cases than 2GB of DDR). CAS4 stuff is another $50 bucks. But CAS3 @ 800MHz will cost you big.
Note: Just about any PC2-6400 (800MHz) memory is CAS3 at a lower speed. For example, running a Conroe using 1:1 FSB:RAM (synchronous) gives a memory speed of 533MHz (which is PC4200 speed). This in dual-channel perfectly matches the CPU's 8.4 GB/s bandwidth. In theory, more memory bandwidth shouldn't be any faster, and there is also a latency (or time delay) introduced because of asynchronous operation.
So I am running my CAS4 OCZ @ 533MHz with very tight CAS3 timings.
Now, the Athlon guys can run a full 1:2 ratio - at which point the enormous bandwidth makes a little asynchronous latency nothing to worry about.
As a new Intel Guy (still an AMD guy also) but as an Intel guy I say, Show me PC2-8400 @ 1066MHz! Then I too will run 1:2 ratio.
But that stuff costs BIG, even CAS5...
Regards

Thanks, but I have no idea what the hell you are talking about! I am new to this! Can you simplify please? Are you talking about overclocking?

I will OC a little...I'll be getting an E6600 and will push it to 3.2-3.4ghz.
August 13, 2006 3:57:04 PM

Get cas 4 - that way, you'll get better performance, but not at expensive as cas 3.
August 13, 2006 4:40:17 PM

Quote:
Thanks...but what about the next 3 numbers? Lower is better with them, too?

For all numbers (5-5-5-12), lower is better.

If lower is better for all numbers than why is the last number for OCZ platinum 15 and 12 for the OCZ gold? (Gold is 5-5-5-12, platinum is 4-5-4-15)
August 14, 2006 2:50:10 AM

Quote:
Thanks...but what about the next 3 numbers? Lower is better with them, too?

For all numbers (5-5-5-12), lower is better.

If lower is better for all numbers than why is the last number for OCZ platinum 15 and 12 for the OCZ gold? (Gold is 5-5-5-12, platinum is 4-5-4-15)

This is a common misconception. The last number is the time between active to precharge. Here, and here only, sometimes a larger number is better. Think of it as an amount of time to read a page of a book before the book gets closed and then reopened so you can read again. The longer the time, the more you get to read before the book closes. If the other timing numbers are sufficiently fast, then the last number can go down and still be good. The OCZ platinum would be the better ram in this case.
!