System Clock :

A system clock or system timer is a continuous pulse that helps the computer clock keep the correct time. It keeps count of the number of seconds elapsed since the epoch, and uses that data to calculate the current date and time.

Bus Clock :

In a simple computer architecture with a single active CPU connected to RAM and other passive peripherals by a bus, then there is a timing signal (typically produced by a quartz oscillator) that synchronises the internal operation of the CPU. This clock signal is the system clock.

There may also be a separate timing signal that synchronises the activities of writing to and reading from the bus. This is the bus clock. Because the speed at which data can be reliably transmitted across the bus may be lower than the internal speed at which the CPU runs, the bus clock signal is usually at a lower frequency than the system clock. The bus clock signal may be produced by passing the higher frequency system clock signal through a frequency divider.

• Main difference between system clocks and bus clocks as follows:

                 The system clock regulates the CPU and other components (including the buses). there are however, some bus clocks which                      regulate themselves or, in other words, function according to their own clocks.