I am planning to replace my 3 year old computer. Currently my e6750 runs on DDR2 800 with CAS 5.
Since I'm planning to get the i7-870, I was looking at 1333Mhz sticks.
Can someone tell me if this calculation is any good:
800Mhz CAS4 = 1/400 = 2.5ns/tick = 12.5ns/transfer
1333Mhz CAS 9 = 1/666 = 1.5ns/tick = 13.5ns/transfer
I find it very hard to believe that DDR2 beats DDR3. So what am I missing here !?
You are comparing low latency DDR2 with high latency DDR3. It would be more fair to compare your old RAM with Cas 7 DDR3-1333. There might be some archetecture advantages also. In any case the jump from DDR2 to DDR3 is not that big of a deal. You also dont have any choice so it doesnt really matter.
It looks like your math is close, but as dndhatcher points out, 800 MHz CAS 4 is pretty much top of the line DDR2, while 1333 MHz CAS 9 DDR3 are bargain bin sticks (mostly). Comparing to CAS 6 or CAS 7 would be a more appropriate comparison.