Introducing UNIX and Linux

The Computing Environment

Overview
What is a Computer?
Hardware
      Processors
      Input Devices
      Output Devices
Software
      Input and Characters
            Control Characters
      Application Programs
            Programming Languages
      The Operating System
      System Administration
History of UNIX and Linux
Conventions
Summary

Output Devices

Output devices are also varied, and we will focus primarily on the screen or monitor (or even VDU (Visual Display Unit) - to use a somewhat out-of-date expression) that typically comes as part of the package with the processor and the keyboard.

In the past, people used so-called dumb terminals, which are largely redundant now. A dumb terminal consists of a keyboard and a screen, and can display only the same sort of text and simple characters as a typewriter. On the screen is a cursor, which is either a block (a filled rectangle the size of a letter) or an underscore, marking the point on the screen at which typed characters appear, and also where any message the computer writes will begin. The equivalent of a dumb terminal is now more commonly referred to as a command window in many systems.

These days, modern computers are typically made up of a screen (to display both the input that is provided through keyboards, for example, and any results of the processing performed), a keyboard and a mouse. The configuration is sometimes referred to as a graphics terminals, to distinguish it from a dumb terminal. These are capable of much more sophisticated output. In particular, the screen is a high-resolution display (nearly always colour), allowing complex graphics to be drawn as well as simple characters. Usually, a system is employed by which the screen is divided up into rectangular areas called windows, with which to communicate individually. The computer itself may be a PC, a workstation or a laptop, but that is not important. We will assume the use of a command window, which applies to all equally. If you are using any of these, you can create such a window, which behaves as if it were itself a dumb terminal, having its own cursor. Typically, there is also a global cursor that moves each time you move the mouse; you can select which window the keyboard will communicate with by moving the global cursor so that it is within the chosen window.

The look and feel of the various kinds of computers can vary enormously, as can the way in which windows on a screen are manipulated. Either a window manager or a desktop manager can be used to control the windows on a screen, and though the distinction between the two kinds of software is somewhat blurred, a desktop manager typically has more features and capabilities than a window manager. We will go into more details about these later.

These basic components of processor, screen and keyboard are the key pieces of the modern computing system, and their combination underlies all of the details that follow in this book.