Theoretical RAM question...

[astroview]

Right now the new P4s are using an 800 Mhz bus w/ 200 Mhz Ram that is DDR and dual channels on the motherboard that makes it 800 Mhz.

Is this as fast as a stick of RAM that was actually 800 Mhz instead of using the DDR/dual channel "tricks?"

Theoretically they are the same right? But in reality would it be the same? I realize that RAM running at 800 Mhz w/o the DDR technology does not exist yet.

 

[Lord Evermore]

The data throughput is as fast, because it does physically transfer two times for every cycle of the clock. However DDR memory only uses one cycle for address transactions, so that only works at the actual frequency. I guess they decided it worked well enough to not implement addressing on both sides of the cycle.

I think the result is that if a transfer only takes half a cycle, then the remaining half cycle is lost because an address request can't be sent until the cycle after that. Since pretty much every transfer will take way more than one full cycle, the loss is minor. If a transfer takes 10.5 cycles (21 "bits" of data), then the last half cycle is lost, and then the next cycle begins and an address is sent.