Originally posted by QCassidy352
"OK, this is kinda funny. The 970 is announced with a double pumped 450MHz bus and mac users go insane over it. The Pentium 4 is announced with a quad pumped 200MHz bus, and everyone goes 'oh, it's not actually 800MHz, it doesn't matter'. "
agreed. whatever it is technically
It is NOT a technicality, and dismissing it as such simply demonstrates the complete lack of information that is circulating out there.
The following is undoubtedly something of a simplification, but hopefully the basic point is nevertheless clear.
There are two dimensions that effect memory performance: bandwidth and latency. Bandwidth you can think of as being the total amount of information that can be moved in a unit of time, and latency you can think of as being how long it takes to find and begin transferring that information. If you think of it in terms of a hard drive, bandwidth corresponds to the peak transfer rate (e.g. 40 MB/sec) and latency corresponds to the access time (e.g. 6 ms).
The key thing is that double-pumping (or quad-pumping) doubles (or quadruples) the theoretical peak bandwidth, but does essentially NOTHING to improve latency. The bus can now transfer twice as much information with each clock cycle, but the clock cycles aren't coming any faster. Therefore, for applications in which latency is more important than bandwidth, using a 167 mhz bus can actually be faster than using a double-pumped 133 mhz bus (what you would erroneously refer to as "266 mhz"). These applications would be ones which need to access lots of different pieces of information.
The bottom line is that all other things being equal, a double pumped 400 mhz bus is better than a quad pumped 200 mhz bus because they both have the same theoretical bandwidth but the former has better latency than the latter. Likewise, an 800 mhz single data rate bus would be better than either.
Now, in this specific case I believe it doesn't matter as much because the fastest DDR memory currently available, DDR400, is just double pumped 200 mhz memory, and presumably having your bus run at twice the frequency of the memory is not all that useful in terms of reducing latency (they use dual-channel to get the memory bandwidth to match up with the FSB bandwidth). But in general it is important to note that double-pumping is NOT exactly the same as just doubling the clock speed, because latency DOES matter!
