In microprocessors, the clock rate is decisive for the operations that can be executed in one second, the operations per second( ops). A distinction is made between the internal and external clock frequency.
The internal clock frequency is the frequency at which the central processing unit( CPU) internally processes instructions, also known as the CPU clock. These clock frequencies have evolved over the last two decades from a few megahertz( MHz) to several gigahertz( GHz). The external clock frequency, also known as the system clock, is the frequency at which the microprocessor accesses the Level 2 cache and memory. The internal and external clock frequencies are directly related to each other.