# How Do People Tell Computers What To Do?

Computers don’t understand words, but they do understand numbers. So when a computer operator wants to tell a computer what to do, he or she has to translate any instructions into numbers.

The number system that computer operators use to “talk” to computers is called the binary system. It is different from our number system, the decimal system, which is based on the number ten, with each “place” ten times higher than the place to the right of it. For example, in the number 173, the 1 stands for 100, because it is in the “hundreds” place; the 7 stands for seven tens, or 70; and the 3 stands for three units, or three.

In the binary system, there are only two numbers, one and zero. Each place in a binary number is two times higher than the place to the right of it. So, the binary number 111 stands for one 4, one 2, and one 1, for a total of seven. Counting to ten in binary numbers, we have: 1, 10, 11, 100, 101, 110, 111, 1000, 1001, 1010.

In the binary system, large numbers require many digits. But the binary system has one big advantage for use in computers. A computer is an electronic machine, and can read a one or a zero as an “on” or “off” electric switch.

A computer operator can tell a computer anything he or she wants to by using these numbers. A computer punch card with holes in it contains that information: Each hole stands for a one, and the lack of a hole in a certain place on the card stands for a zero.

Some computers can perform 36 million operations in just one second!