In a computer, the clock cycle is the time between two adjacent pulses of the oscillator that sets the tempo of the computer processor. The number of these pulses per second is known as the clock speed, which is generally measured in Mhz (megahertz, or millions of pulses per second) and lately even in GHz (gigahertz, or billions of pulses per second). The clock speed is determined by a quartz-crystal circuit, similar to those used in radio communications equipment.
Some processors execute only one instruction per clock cycle. More advanced processors, described as superscalar, can perform more than one instruction per clock cycle. The latter type of processor gets more work done at a given clock speed than the former type. Similarly, a computer with a 32-bit bus will work faster at a given clock speed than a computer with a 16-bit bus. For these reasons, there is no simple, universal relation among clock speed, "bus speed," and millions of instructions per second (MIPS).