which memory: faster clock or lower latency?

[AlpineCarver]

i'm thinking about a possible new build, using:

• motherboard - Asus M4A785TD-M EVO
  CPU - AMD Phenom II X4 965 Black Edition Deneb 3.4GHz Socket AM3 125W

no overclocking.

i have two 2x2GB ECC memory choices from crucial:

• CT2KIT25672BA1339 • CL=9 • Unbuffered • ECC • DDR3-1333
  CT2KIT25672BA1067 • CL=7 • Unbuffered • ECC • DDR3-1066

they're exactly the same price. which would perform better in the target system?

there's also this one, which is a bit less expensive:

• Kingston DDR3-1333 ECC Unbuffered KVR1333D3E9SK2/4G (CAS latency 9)

are there any other DIMMs you would recommend over these?

thanks.

[swivelguy2]

Faster clock speed generally produces more memory bandwidth than tighter timings. However, it's very possible that the two kits are the same memory chips, but with different XMP settings (the unit on the memory that tells the motherboard's BIOS what the rated speed of the memory is).

[theycallmebruce]

Memory latency is tricky, because it is specified in terms of clocks.

So:

a CAS latency of 7 @ 1066MHz equates to 6.56 nanoseconds
a CAS latency of 9 @ 1333MHz equates to 6.75 nanoseconds

The CL7 RAM is only 2% faster to access a memory column in absolute terms.

As for real world performance, I don't know, but I'd guess swivelguy is right. Bandwidth is probably more important than latency for most applications. Either way, I suspect the differences would be imperceptible unless your application is long running and RAM-bound, which is probably not the case for most commonly used software on desktop PCs.

Personally I'd go for Kingston, simply because I've had a good run of reliability from their RAM and they are well priced.

[Cistron]

How about simply buying more generally cheaper RAM? Wouldn't that have the most effect?

[dragonfire]

I don't think you'll see much benefit past 4GB of RAM in most situations. With the exception of video encoding, it is very difficult to max out the full 4GB with desktop apps or games.

[swivelguy2]

If you're concerned mainly with pure blistering memory speed, don't use more than 1 DIMM per channel in order to go past 4 GB. You generally can't run as high speeds or as tight timings with 2 DIMMs per channel.

Then again, if you're concerned with memory speed that much, get an i7-920, because having a third memory channel blows away all speeds of 2-channel RAM.

[smilingcrow]

The trade-off between speed and latency varies depending on what applications you are using. In your case the DDR3-1333 CL9 makes more sense as it has a higher bandwidth and the ‘actual’ latency of the two sticks is very similar.

[AlpineCarver]

thanks, everyone, i really appreciate the help.