|You can only run dual channel configuration if your motherboard supports it.|
Here's the mathmatical theory behind it (hang in there)...
1st, you have to understand that the P4's FSB is "quad-pumped" so even though the FSB for your CPU is called 533MHz, it's actual setting is 133MHz. (4 x 133MHz = 533MHz). The 533MHz is the "effective" FSB speed.
At 533MHz FSB, the CPU's bandwidth is approx 4267MB/sec. This is calculated by mutiplying the "effective" FSB by 8. At 400FSB, the CPU's bandwidth is 3200MB/sec (400 x 8), & at 800FSB, the bandwidth is 6400MB/sec (800 x 8).
DDR-SDRAM is rated for the amount of bandwidth it can handle at a given speed...this is more appropriately called the RAM's "throughput". Throughtput is calculated by multiplying the "effective" RAM speed x 8. Remember that DDR-SDRAM is "double-pumped":
DDR266 (PC2100) = 133MHz x 2
DDR333 (PC2700) = 166MHz x 2
DDR400 (PC3200) = 200MHz x 2
For example, PC2100 can handle 2100MB/sec at 133MHz, but if you run it at 100MHz, it can only handle 1600MB/sec (100MHz x 2 x 8).
Hopefully this is making sense...if not, it should all fall into place in a minute...
The most important thing to know is that for best performance, the CPU's bandwidth & RAM's throughput should be in balance.
Using your 533FSB CPU as an example, there is no RAM that runs at 133MHz & has a throughput of 4264MB/sec. However, if your board supports dual channel mode, two sticks of PC2100 running at 133MHz have a combined throughput of 4200MB/sec**. You can run either PC2700 or PC3200, but to keep it in balance with the CPU, they should be run at PC2100 speed. If your board only supports single channel mode, there is no way to balance the CPU & RAM...no matter what you do, the RAM will always be the system's bottleneck.
Does that make sense?
** The true troughput of PC2100 RAM is 133.3333MHz x 2 x 8 = 2133.33MB/sec...in dual mode, that would be approx 4267MB/sec
1800+ @ 8.5 x 200MHz
768MB PC3200 2.5-3-3-7
Asus A9550GE/TD 128MB