Machine Language Program

There are at least two sensible programs for the toothbrush. Here is one program:

Address	Machine Instruction	Meaning
0	0000 0001	Rotate bristles left
1	0000 0010	Rotate bristles right
2	0000 1000	Skip next instruction if switch is off
3	0000 0100	Go back to start of program
4	0000 0000	Stop running

In the electronic memory of the toothbrush the program is stored as a sequence of bits:

0000 0001 0000 0010 0000 1000 0000 0100 0000 0000 

The processor starts at the beginning and performs the action described by each code. This is, of course, a stupid example. Electric toothbrushes are not controlled by computer processors. And, the machine instructions of actual processors are much more detailed. But the essential ideas of the example are these:

• A machine language program is a sequence of machine language instructions in main memory.
• A machine instruction consists of one or more bytes (in the example, only one.)
• The processor runs a program one machine instruction at a time.
• All the little machine operations add up to something useful.

If toothbrush user leaves the switch "on" for a while, the program repeats its operations many times. This is how most programs in real computers run--many little operations add up to a useful function, which is then repeated many times.