Newbie questions regarding memory numbers

Please help out a computer newbie in clearing up some misunderstandings.

I’ve been reading forums and wondering what memory to get for a future 2.4c(which I’ll purchase after 26oct). I’ll get either an IC-7 or a P4C800 Deluxe. I’ve heard IC-7 is bad with memory selection so I’m willing to get the Asus. I’m also aware of the BH-5 and CH-5 problems on 875. But anyways.

My real problem is with memory/memory ratios and speeds. I see numbers everywhere and I don’t understand what they mean. What is 1:1 ratio? What is 5:4 or 3:2? Which is better? Memory for example is displayed as PC3200 400MHZ. How do people come out with 230-250 FSB when it says 400? I’m really confused. Would someone please explain what the ratios, memory frequency and cas timings have in common and what do they mean?

1:1 Ratio means that the memory runs synchronously with the CPU on the FSB. For example on my Abit i run my board at 217 FSB at a 1:1 ratio. This in turn translates to my memory running at 434mhz (217 x 2) since the RAM is DDR (Double Data Rate = multiply the FSB x 2 to get your RAM Speed according to your FSB). Then take the 217 and multiply it times your CPU multiplier and you will get the speed of your CPU. Mine is at a 10 multi currently so i get 2170 mhz on the CPU.

Due to the high overclockability of the 2.4C, the locked multiplier of 12, and the FSB limitations in order for you to run it at speeds higher than 3.0 ghz you are forced to use a 5:4 or 3:2 ratio. Even with PC4000 (500 mhz DDR) if you were to run in synch (1:1 ratio) at stock settings the highest the 2.4C would go is 3.0ghz (12 x the 250 FSB). So in order to get the high 3.6ghz that alot of people have been getting with the 2.4C it is necessary to run the memory asynchronously to take advantage of the processors overclockablility. For example at 300 FSB the Processor will run at 12 x 300 - 3.6ghz but theres hardly any RAM that will run at that speed sychronously (Yes it exists but requires very lax memory timings and good RAM). So to use PC4000 that runs at stock 500 mhz (250 mhz DDR) at that FSB you have to use a 5:4 Ratio. A simple equation such as this can be used to figure it out:

((FSB X 4) / 5) X 2 = Speed of RAM at 5:4 Ratio

((FSB X 2) / 3) X 2 = Speed of Ram at 3:2 Ratio

Use that within the limits of what your P4 2.4C can run at and tweak as need be with the Ratio's and the FSB. Im sure someone with a P4 system such as Larva could enlighten you even further.

The 400 mhz you are seeing on the RAM is simply what the RAM is rated at. People using a high FSB such as 220-230 are overlclocking their RAM to 440-460 mhz.

For CAS Timings check this out:

http://forum.oc-forums.com/vb/showthread.php?s=&threadid=62006