PowerMac Processors

[Don Cherry]

What is the difference between, let's say a 1.8GHZ single and Dual processor, besides the obvious?

A Dual 1.8, is that two 900MHZ processors or two 1.8GHZ?

What is the performance gap between these?

[Sun Baked]

The SP PowerMac is a iMac in a PowerMac case -- so the single processor chipset (U3-Lite+Shasta) is the consumer chipset with the FSB running at a third of the CPU clock (600MHz.)

The DP PowerMac has the dual CPU capable XServe/PowerMac chipset (U3H+K2+PCI-X Tunnel) run their FSB at 1/2 the 1.8 (900MHz) -- in addition the 2.0/2.5 have a faster HT bus and HT PCI-X Tunnel that the DP 1.8 doesn't include.

The DP are basically twice as fast as the SP machines that take advantage of SMP -- and faster than the SP machines that don't because the OS will split threads between the two CPUs, so an monolithic app that hogs a CPU won't bring everything else to a crawl.