CompTIA A+ Certification All-in-One Exam Guide

Figure 3-10 The CPU often needs more than one clock cycle to get a result.
The maximum number of clock cycles that a CPU can handle in a given
period of time is referred to as its clock speed. The clock speed is the fastest
speed at which a CPU can operate, determined by the CPU manufacturer. The
Intel 8088 processor had a clock speed of 4.77 MHz (4.77 million cycles per
second), extremely slow by modern standards, but still a pretty big number
compared to using a pencil and paper. High-end CPUs today run at speeds in
excess of 5 GHz (5 billion cycles per second). You’ll see these “hertz” terms
a lot in this chapter, so here’s what they mean:
1 hertz (1 Hz) = 1 cycle per second
1 megahertz (1 MHz) = 1 million cycles per second
1 gigahertz (1 GHz) = 1 billion cycles per second
A CPU’s clock speed is its maximum speed, not the speed at which it must
run. A CPU can run at any speed, as long as that speed does not exceed its
clock speed. Many CPU models have the clock speed printed clearly (see
Figure 3-11). Other models might have a cryptic code.