Hackers & Painters

Chapter 10. Programming Languages Explained

Any machine has a list of things you can tell it to do. Sometimes the list is short. There are only two things I can do to my electronic kettle: turn it on and turn it off. My CD player is more complicated. As well as turning it on and off, I can turn the volume up and down, tell it to play or pause, move back or forward one song, and ask it to play songs in random order.

Like any other kind of machine, a computer has a list of things it can do. For example, every computer can be told to add two numbers. The complete list of things a computer can do is its machine language.

Machine Language

When computers were first invented, all programs had to be written as sequences of machine language instructions. Soon after, they started to be written in a slightly more convenient form called assembly language. In assembly language the list of commands is the same, but you get to use more programmer-friendly names. Instead of referring to the add instruction as 11001101, which is what the machine might call it, you get to say add.

The problem with machine/assembly language is that most computers can only do very simple things. For example, suppose you want to tell a computer to beep 10 times. There’s not likely to be a machine instruction to do something n times. So if you wanted to tell a computer to do something 10 times using actual machine instructions, you’d have to say something equivalent to:

 put the number 10 in memory location 0 a if location ...