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RAM latency confusion

Last response: in Memory
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May 10, 2012 6:18:25 AM

Hello, I recently have been reading up about RAM and it made me realize that I do not need to buy RAM that runs at 1666mhz and the difference between it and ram that runs at 1333mhz is practically non-existent.

I read that the numbers separated by dashes x-x-x-x-x represent latency and (despite being a bit tricky to understand) it all boils down to go for lower numbers, lower numbers mean faster timings. Simple enough right?

So why does slower ram have lower latency?

Corsair Vengeance 8GB (1x8GB) DDR3 PC3-12800C10 1600MHz
at latency settings of 10-10-10-27

OcUK Value 8GB (1x8GB) DDR3 PC3-10666C9 1333MHz
Cas latency: 9-9-9-24-2N

Novatech 4GB (1x4GB) DDR2 PC2-6400C5 800MHz
CAS 5-5-5-15 Timings


How do I know what is actually faster? The numbers contradict each other.

More about : ram latency confusion

a b } Memory
May 10, 2012 6:26:03 AM

you can rule out the 3rd one because the difference between ddr2 and ddr3 is large enough
May 10, 2012 6:51:14 AM

Ok, so the different ddr's are not comparable OK, that makes sense.

But how can 1333mhz ram running faster than 1666mhz ram make sense? When going for the fastest ram which numbers do I take into consideration.

I am thinking of going for the 1333mhz ram, simply because of the article I read showing that 1666mhz is not really necessary for me. I'd still like to understand what I'm reading though before I commit to the purchase.
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a b } Memory
May 10, 2012 2:02:19 PM

The real latency is not measured in clock cycles, it is measured in nanoseconds. You get the real latency by dividing the cycle count by the clock frequency: 7 / 1333MHz = 5.25ns while 9 / 1600MHz = 5.63ns

Higher clock rates provide higher burst data rates but often at the expense of higher effective latency. Memory throughput is more important for linear data processing like video encoding/decoding while lower latency is more important for non-linear applications like compiling code. Most applications such as games are a mix of both.
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