CompTIA A+ Certification All-in-One Exam Guide

By placing machine language commands—called lines of code—onto the
EDB one at a time, you can instruct the Man in the Box to do specific tasks.
All of the machine language commands that the CPU understands make up
the CPU’s instruction set.
So here is the CPU so far: the Man in the Box can communicate with the
outside world via the EDB; he has four registers he can use to work on the
problems you give him; and he has a codebook—the instruction set—so he
can understand the different patterns (machine language commands) on the
EDB (see Figure 3-8).
Figure 3-8 The CPU so far
Clock
Okay, so you’re ready to put the Man in the Box to work. You can send the
first command by lighting up wires on the EDB. How does he know when
you’ve finished setting up the wires and it’s time to act?
Imagine there’s a bell inside the box activated by a button on the outside
of the box. Each time you press the button to sound the bell, the Man in the
Box reads the next set of lights on the EDB. Of course, a real computer
doesn’t use a bell. The bell on a real CPU is a special wire called the clock