Those numbers are access times and are just recommended timings for that particular speed. The numbers are in nanoseconds and are basically a measurement of the delay of the process when memory receives an instruction retrieves data and sends it back. The first four numbers stand for:
• RAS - Row Address Strobe or Row Address Select
• CAS - Column Address Strobe or Column Address Select
• tRAS - Active to precharge delay; this is the delay between the precharge and activation of a row
• tRCD - RAS to CAS Delay; the time required between RAS and CAS access
The two most important things you balance for your RAM on your BIOS settings are RAM speed and RAM timings. The box has recommended settings, but most DDR2 667 RAM can be over clocked to DDR2 800 with a slight increase in voltage and lower RAM timings.
However most articles I’ve read have pointed out that sacrificing the RAM timings for RAM speed always lead to higher gains in frames per second, and is worth the RAM timings delay.
If you want to over clock your processor, then you should have RAM that can run at DDR800. If you have an E6400, you owe it to yourself to over clock it. It is the king of OC processors and you should be able to run it at E6700 speeds. Granted you need a good mobo, but quality RAM makes a massive difference. I am currently running my E6400 at 2.84, game stable.
To over clock your processor you increase your CPU FSB speed and use that with the multiplier. For example if you set your E6400 Front Side Bus speed to 350, since it comes with a lovely multiplier of 8, you get an overall speed of 2.800. To set a bus speed that high you need to feed your CPU a bit more voltage so you up that to 1.30V, which is more than enough, and extremely safe.
Now there is something called a FSB: DRAM divider. Basically your RAM should run at at 2x the FSB for the smoothest operation.
For example if your FSB is set to 350 then your RAM should be 700 to get a divider fraction of 1:1.
Most hardware sites and gamers have their fraction set at 4:5 and it is the most accepted fraction, but they say the smoothest should be 1:1. However 4:5 is pretty standard now.
But the point of telling you all that is that as you increase your FSB, your RAM speed goes up (unless you drop the divider)… and as your RAM speed goes up, you need to increase voltage and drop the RAM timings, unless your RAM is rated to run at those timings at that high a speed.
For example if your DDR2 800 RAM is rated at 4,4,4,10… then you are beautifully set. Though even at something like 5,5,5,15 you won’t see that big a loss, since like I said it seems to come down to speed a lot more.
But say you had DDR2 667 rated at 3, 3,3,10 and you wanted to over clock your processor, while maintaining a 1:1 divide. Chances are that at that speed the RAM wouldn’t be able to handle the lower memory timings, so you would decrease the timings and run a RAM stress test called Orthos.
Over clocking takes a bit of trial and error. You can increase your memory timings bit by bit and run the RAM stress tests.
During my over clocking experiments my comp restarted maybe twice, before I was happy at 2.84. As long as you don’t do anything dangerous with the RAM or CPU voltage you will be fine.
Most RAM can safely go to 2.1V and CPUs can go to 1.34V.
If you don’t go beyond that you will never have any issues. Meanwhile you can experiment with things like RAM timings, but I played it safe.
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2802&p=2
