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RAM speed vs CAS timing

  • Memory
  • DDR2
  • RAM
Last response: in Memory
March 7, 2009 12:48:00 AM

I currently have 4GB of DDR2 800MHz 4-4-4-12 RAM. I am looking to upgrade to 8GB of RAM (yes, I have a 64-bit OS) and can either add another 4GB of the same or upgrade to 1066MHz DDR2.

The difference is that the 1066MHz RAM has 5-5-5-15 timing.

Is there a big enough difference for me to buy 8GB of the 1066MHz 5-5-5-15, or is the difference so small that I'm better sticking with the 800MHz with the better CAS latency timing?

More about : ram speed cas timing

a c 115 } Memory
March 7, 2009 1:51:51 AM

You'd have to run benchmarks to detect the additional performance of 1066 MHz RAM.
a b } Memory
March 7, 2009 7:24:49 AM

You are better off with the DDR2 800. You can slightly OC the DDR2 800 to reach the same performance as the 1066 at a cheaper price.
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a b } Memory
March 7, 2009 10:06:33 AM

Why do you need 8 gig of memory....?
a b } Memory
March 7, 2009 4:29:31 PM

It's not always about need :) 
March 7, 2009 5:05:08 PM

As my new best friend Bilbat learnt me this morning.

At 1066, a ram bus cycle, rising edge to rising edge, is 1000/1066, or .936 nanoseconds; at 1333, it is 1000/1333, or .75 nanoseconds; (CAS)5 x .936 = 4.68 nanoseconds per memory transaction; (CAS)9 x .75 = 6.75 nanoseconds

But in your case it would be 1000/800 = 1.25 ns * 4 = 5 ns per memory transaction.


1000/1066 = 936 nanoseconds * 5 = 4.68 ns per memory transaction.

So very very close on a theoretical latency basis.

I'd say stick with the DDR2 4-4-4-12 at 800MHz.
March 9, 2009 12:16:19 AM

Thank you all for your responses, and thank God I comprehend the maths...

I'll be sticking with the 800.

And as far as 8GB is concerned - 64-bit OS, no pagefile.

Oddly enough, this now means that this computer has as much ram as my first computer had hard drive...
a b } Memory
March 9, 2009 8:26:26 PM

honolululu - Not disagreeing with you in end result.
Math alittle off but comes out in the wash. @ Clock freq for DDR2-800 is 400 MHz
which is 2.5 nansseconds. With DDR that means 1 transaction on leading edge and on transaction on laging edge. equivalant to SDR runing at 800 MHz. The 2 in DDR2 doubles that as the two sticks are effectively operating in Parallel - hense Fronside bus = 1600.

Overall excellent comparrison. Don't forget that while the first digit(4-4-4-12) is most important the other numbers also effect performance
March 10, 2009 2:54:08 AM

Indeed they are all important - after starting this thread, I went on an information bender and found a number of reviews on my RAM (2x2GB kit of Crucial Ballistix DDR2 800MHz 4-4-4-12) some on Tom's.

It's apparently one of the most overclockable RAM kits in its class:

I made an awesome choice, and I wasn't even trying for it...

(note that the review I linked is an older one, and states that the ram I have runs at 2.10v for the 800MHz 4-4-4-12 timing - the ram has since been upgraded and runs stable at that speed and timing at 2.00v)