What A Computer Can And Cannot Do?

Amazingly, a computer can only do one simple thing: It can subtract one binary number from another and replace the original one with the result. Its power is that it can do this simple thing four billion times per second.  Programming provides a pattern of such numbers, so that the computer always has a new number to subtract and a place to store the result.  When connected to a storage device such as a hard drive or memory chip, the computer can store and manipulate all sorts of information; connected to a monitor or printer or speaker, it can display the information in the form of language characters or colored pixels or sound waves.  Because it can display all this through a network to another computer on the other side of the world, it is a powerful communication tool.  It can also control machinery by turning switches on and off, but only as it is programmed to do; it never invents new ideas.