[quote]Originally posted by AugustWest:
<strong>That was a helpful description, nut, thanks. While you're on a roll, could you explain how the system bus speed plays into this discussion. For instance, comparing a 100MHz system bus on a cube or iMac (with equivalent chip speeds) to a 133MHz G4 tower, to, PERHAPS, a 233 MHz tower in the near future. For someone doing photo editing in photoshop and some DVD authoring, which factor matters more?</strong><hr></blockquote>
Bus speed advantages depend on how fast the processor is.
So using the example above with all processors @500Mhz, a 100Mhz Bus would be all you needed to feed the processor. The bus is split into the system bus and the memory bus. Both are measurements of how quickly each bus talks to either the memory or the rest of the system and the processor.
When processor clockspeed increases like in a G4/667, then a 133Mhz bus is needed in order to feed it the data faster. This is likely a reason why Apple keeps the lowend Powerbook G4/550 on a 100Mhz bus. There probably wouldn't be much of a distance because there isn't much of a bottleneck.
Right now, Apple's G4 systems DO have bottlenecks. But primarily in altivec enhanced operations which the G4 does so fast that it outpaces the speed at which the bus can feed it data and read the data.
It's been said that as low as a dual/533 G4 has bottleneck problems with the 133Mhz bus.
If Apple upgraded the bus speed to 266Mhz a difference would be seen only in apps that are memory intensive. Photoshop would be one, but it wouldn't be close to an overall gain. It would just be noticeable in the few operations that were bottlenecked (the heavily altivec optimized ones probably).