Originally posted by naerskine
Why when I OC'd my E6600 with my G/skills ddr2 800mhz pc6400 ram why did the ram slow down? (tested latency with Everest went from 68n/s to 90n/s)?
It's all about synchronizing the FSB and the RAM speed. If they are not running at the same speed, the computer can't correctly do things.
The E6600 stock speed is 266 * 9 = 2394Mhz. DDR2-800 RAM is automatically set to a 2:3 multiplier to bring its speed from 266Mhz (FSB speed) to 400Mhz.
To be clear, the RAM is running internally
at 400Mhz (its design speed), but a piece of electronics (the multiplier) downscales that to 266Mhz so that the FSB sees
only 266Mhz, and thus can synchronize. This can be confusing, but if you have any questions, I'll be glad to further elaborate.
Now, you overclocked to 2817Mhz. Here's an example of what could happen. So 2817Mhz means you upped the FSB to ~313Mhz (if you kept the 9x clock multiplier). With the same 2:3 multiplier, your RAM would be pushed to ~470Mhz. That's probably too much, so the BIOS would change the multiplier to bring the RAM back to a compatible speed. It would probably choose a 4:5 multiplier, so the RAM would run at ~391Mhz (Again, this is internally. Externally, the RAM is running at 391 * 4/5 = 313Mhz, the FSB speed). There, your RAM is now running slower than before. In spite of this, you'd still expect a substantial performance increase, due to the CPU overclock.
I just guessed the values here. If you give me more details as to the initial and final speeds of CPU/FSB/RAM, the FSB:RAM multiplier and the RAM timings, we can probably make more sense out of it all.