What is the difference between 800MHz front side bus and 1066MHz front side bus?

Think of the front side bus in your computer as if it were a highway. The faster the bus, the wider the highway. The cars represent the data being sent between the processor and the memory. If you have an 800mhz bus, it is like having, say 10,000 cars on a 4 lane highway. If you have a 1066mhz bus, the highway is widened to 6 lanes with the same amount of traffic. Therefore with the faster bus, there are more lanes for cars to travel on so the traffic moves faster than on the narrower (slower) highway (bus). If you could really use the extra speed (gaming, video editing, CPU intensive work), then you should opt for the faster bus. If two cpus have the same clock rate, architecture and cache size with the only difference being the bus speed, the one with the faster bus will be better. Hope this helps.