FSB SPEED

INTERNAL CLOCK SPEED: CPUs or processors are often graded by their internal clock speed. This speed is the number of operations a processor can perform per second. For example, the Pentium-4 3.0 GHz has a clock speed of 3000 KHz or 3.0 GHz.
EXTERNAL CLOCK SPEED: This is the speed with which the CPU can communicate the rest of the system. The CPU communicates with the rest of the system via a gateway called system bus or front side bus. Hence, the external clock speed is also called Front Side Bus (FSB) speed.
MEMORY CLOCK SPEED: This is the speed with which the RAM is given requests for data.

In old CPUs, the memory clock speed used to be the same as the FSB.

With the Athlon K7 processor, AMD introduced something new. The Athlon processor had an FSB of 100 MHz but the bus could make 2 data fetches per cycle from the RAM. So, the effective rate became 200 MHz. AMD then went on to claim that the Athlon had an FSB of 200 MHz. AMD called this Double Data Rate (DDR) FSB.