Clock speed
From The Glossary of Digital Photography
The speed in cycles per second, or hertz, at which a computer operates. Different sections of a computer will have different clock rates. By convention, clock speed usually refers to CPU clock speed, although the clock speed of the internal bus is very important to the overall speed of a computer. The earliest personal computers had a clock speed of 2 MHz, or two million cycles each second. Modern computers have clock speeds of 2 GHz (two billion cycles per second) and higher. Clock speed is commonly used in comparing computers that have similar chips and architecture, but it is not very useful for comparing computer families. Other factors, including bus speed, will have a great impact on the overall speed of the computer. For example, clock speed is useful for comparing different Macintosh computers, but not as useful for comparing Macintosh computers to PCs.
