How do I calculate which Ram speed to use?

[Hywinder]

I'd like to know if this is the correct way to determine which speed Ram to use.

When determining which speed Ram, is this how?
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Intel P4 Processor

(Example) P4/2.40Mhz/512k/533
Buss speed of processor is 533Mhz = 266Mhz Ram (PC 2100)
Since the processor buss speed is 533Mhz, you'd halve the speed and use that speed Ram.

*****
AMD Processor

Would you use the buss speed as the Ram speed also?

(Example) Athlon XP2600+ (Barton core). Buss speed is 333Mhz, then you'd use 333Mhz Ram modules (PC2700).
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Is this correct? I'm not a tech, but I'm somewhat familiar with working computers, and want to build one. I just don't remember the calculation for determining the Ram speed to use as a it relates to the Processor Buss speed.
Thanks in advance.

[pam123]

You're leaving out the motherboard which has to support the ram.
You can choose ram that's faster than the processor bus speed, in my signature I have 3200(400) ram though the processor bus speed is 2700(333).
Since my motherbord supports it that means that I can over clock the processor.
Intel uses a quad pumped bus, so 200 becomes 800 and 133 becomes 533.

[Negeva]

Works for me!
In your first example of the P4, it has a quad-pumped FSB meaning that it is 133x4=533 thus using DDR 266 is enough, since DDR266 is actually 133x2=266 (due to its double data rate of SDRAM).

Most of the time the motherboard will dictate the highest speed of the memory you can use. Thus using your second example of the Athlon it would, in my opinion be a waste of money fitting DDR400. However I have heard a few people doing that so they overclock the FSB of the chip because they have the extra 'headroom' on the memory speed.

[alfie2]

use micron's website

www.crucial.com

use their website tool to determine your RAM speed for which motherbd.

[Hywinder]

Just what I was looking for!!

Thanks alfie2, and to everyone else that responded. You all help a lot.