A computer is a machine that performs computations.

In a simple computer model, the computer takes input, does computations, and produces output. There are more involved models.

A calculator is a manual calculating device. Question: How is a computer different from a calculator?

A computer is a calculator that pushes its own buttons.

It does this by a stored program code of instructions.

The computer will do exactly what the instructions say.

The computer will do exactly what you tell it to do. How can that cause a problem?

At one time, computers were called electronic digital computers.

Question: What was a computer before the advent of electronic digital computers?

Before the advent of electronic digital computers, a computer was a profession.

A person could work as a computer (using a calculator), much like a person could work as a printer, a doctor, a lawyer, etc.

All of the jobs for human computers have long since disappeared.

A general DFD (Data Flow Diagram) of a computer model includes

• input,
• output
• storage, and
• processing.

Even a wristwatch has input, output, processing, and storage.

Does anyone still use a wristwatch? What is the input for a wristwatch?

Computers can be very useful.

Have you heard the following saying?

You should do it right the first time.

Can you actually do this? Why or why not?

If you believe in always "doing it right the first time", then try writing a paper with a manual typewriter, from beginning to end, in one try.

What is a more realistic philosophy?

A more realistic philosophy is as follows.

Try do to it right the first time, while making it easier to do over the second time.

This is where the storage aspect of computers is critical.

You can work on a document, save what you were doing, and then, later, pick up where you left off.

Traditional adage: Measure twice, cut once.

In programming terms: Think about what will happen before changing your program. Be ready to go back to the previous version.

Generalization: Keep doing it until the result is acceptable or until a fixed point is reached.

Hardware consists of physical entities, such as computer chips, display monitors, printers, etc. A device is a piece of hardware.

Originally, hardware was hard to change. Today, it is easy to change.

A computer program is a specification of a computation.

A computer program contains the instructions that the CPU of the computer follows in order to accomplish the desired actions.

A computer is like a calculator that pushes its own buttons.

Software is a collection of one or more computer programs containing computer instructions that (should) provide value to the user is called software. Software in the form of programs are the instructions that allow a computer to push it's own buttons.

Originally, software was easy to change (i.e., as in molded). Today, it is hard to change.

Hardware is "hard" because it is difficult to change. Software was originally called "soft" because it was easy to change. ... this notion that software is easy to change has become one of the most pernicious ideas in software development. ... requirements changes - attempts to take advantage of software's supposed softness ... can destabilize a product to such a degree that it can't be finished at all. McConnell, S. (1999). After the gold rush: creating a true profession of software engineering. Redmond, WA: Microsoft Press., p. 19.

Input devices get data into the computer.

What are some examples of input devices? Here are some examples of input devices.

• keyboard
• mouse
• scanner
• camera
• microphone

Output devices display data/information to the viewer.

What are some examples of output devices?

• screen (produces soft-copy)
• printer (produces hard-copy)
• speakers
• plotters