The Idea Behind Computing

• The numbers come from somewhere. Perhaps they come from the records of your monthly spending.

  For the computer, information that comes from somewhere is called input.

• You do something with the numbers: you add them to produce a sum. The sum did not exist until you performed the addition.

  Using existing information to produce new information (or to change the content or nature of existing information) is called processing.

• The result (the sum) you obtain goes somewhere. You might add it to the records of your yearly spending.

  Sending (or saving or storing) information somewhere is called output.

Your mental computer

Over and over again throughout this process of adding numbers, you are taking in information, recording information, moving information from one place to another, and manipulating existing information to produce new information.

In our day-to-day lives, we use input and output so automatically that we have to stop and think before we realize exactly how much input and output is occurring.

We you see a number written on a piece of paper, the image of the number enters your mind. That is input. If you then turn around and write that number on another piece of paper, you move the image in your mind onto the paper. That is output.

It does stretch the imagination, but what the paper "receives" when you write down a number is input for the paper.

If you write down a series of numbers on the paper and then perform addition, you are engaged in a startling number of input-output exchanges.

Somewhere between taking two numbers into your mind and writing down their sum, the mental steps required to perform addition come into play. In these steps, your mind does what the system processing unit of a computer would do: joins two (or more) numbers to create a third number. This is processing.

	TIP: Input and output are so closely associated in the operation of computers that they are almost considered a single process: Input/Output, sometimes abbreviated as I/O.

Because the sum is important in your budget, you "output" it once again, perhaps to an accounting ledger, and record it for future use. Having recorded this important information, you are free to turn to other tasks, assured that you can retrieve the information when you need it. The computer, too, records information (in files—in its own memory, on disks, or on tape) for later retrieval.

	TIP: For the computer, "forgetting" something happens when you turn off the power or erase a file from a disk or a tape.

So a computer is....

You can think of a computer as the sum of all of its pieces of hardware. If you include all of its software in that definition, you are closer to the truth. And if you go no further, you have an entirely workable definition.

Here you are invited to consider the computer, too, as the sum of the processes (actions) that it performs.

Considered as the sum of its processes, a computer truly is whatever the computer is doing when you use it. This may sound strange. But consider what a carpenter is. A carpenter is someone who.... Now, list all the things that a carpenter does. The list could be very long.

The carpenter may also be a parent, a loving spouse, an avid photographer, an active participant in community affairs. The human being who is all of these things is doubtless a very complex individual. Yet, when you hire the carpenter to build something, you hire the knowledge, skills, and activities that make the person a carpenter. In that sense, a carpenter is what a carpenter does. In that sense—in a very restricted sense—a carpenter is a "process."

In a similar fashion, the computer follows command or program instructions in order to take on the role of report writer, document printer, accountant, record keeper, assembly line coordinator, product designer, mail deliverer.... The list goes on and on.

In its simplest activities, a computer takes and records information.

When necessary, it "remembers" what it recorded. When instructed to act, it applies appropriate rules (found in programs) to the information it has and displays or records the results. When necessary, it moves information from one place to another.

The information might be numbers, or letters of the alphabet, or words, or illustrations, or some combination of them. Some computers even work with sounds.

What is your computer right now? It is what you instruct it to do—assuming that it is able to carry out your instruction.