How is CPU speed calculated?

Answer 1

CPU speed is calculated off of the Front Side Bus (FSB) speed and the CPU Multiplier. Don't confuse HyperTransport (HT) or Quad Data Rate (QDR, aka Quad Pumping) with FSB. HyperTransport and QDR have "replaced" FSB, but they too rely on the FSB. FSB was formerly used as a transport medium for data between the processor, memory and northbridge chipset and is now used more just as a reference clock frequency.

FSB * Multiplier = CPU Speed

For example, my Sempron 3400+ runs at 2.0 GHz with an 800MHz HyperTransport bus. It runs on a 200 MHz FSB bus and has a multiplier of 10. The HyperTransport multiplier is 4.

200 MHz FSB * 10x Multiplier = 2,000 MHz CPU

200 MHz FSB * 8x HT Multiplier = 800 MHz HyperTransport bus