Input and Output devices

According to the definition given in the section 1.2 above. We need some device(s) to enter the data into the computer (input devices) and some device(s) to see the outcome (or processed information) of the computer (output devices). Both are discussed as below:

1.2.1 Input devices

Sometimes, the data is entered directly to the computer and sometimes indirectly. In the first case, the data goes directlyto the computer from the source and in the second case; we have to carry out some intermediate handling. In either case the task is to gather data to be processed by the computer. There are three general types of input hardware, namely:

  1. Keyboards
  2. Pointing devices
  3. Source data-entry devices

Keyboard: the keyboard may look like a typewriter keypad to which some special keys have been added. The keys normally available on the keyboards are numeric, alphabetic, function and additional special-purpose keys. Figure 1.2 shows the complete layout of an extended keyboard on a personal computer. It has some additional keys between the main keypad and the numeric keys, and status lights in the upper-right corner. This standard keyboard is also called “QWERTY”, which describes the beginning keys in the top row of alphabetic letters.

Function keys: the function keys are an easy way to give certain commands to the computer. The particular software we use defines what each function key does.

Main keyboard: the main keyboard includes the familiar keys found on a typewriter keypad, as well as some special command keys. The command keys have different uses/effects that depend on the software being used. Some of the most common uses are listed here:

101 –Key “Enhanced” Keyboard Layout extra buttons and keys are based on this layout.

A 101-key-Enhanced-keyboardFigure 1.2:A 101 –key “Enhanced” keyboard, showing the layout of the various key groups.

esc-key       The Escape key, is used in different ways by different programs; often It allows to “escape” to the previous screen of the program.

tab-Key  The Tab key, is used to tab across the screen and set tab stops as on a typewriter.

key_Caps_LockWhen the CapsLock key is pressed, upper case letters are produced. Numbers and symbols are not affected. The number or symbol shown on the bottom of a key is still produced. When the CapsLock is pressed, the status light under “CapsLock” lights up.

shif-key-buttonThe Shift key is pressed in combination with other keys to produce upper case letters and the upper symbols shown on the keys.

ctrl-keythe Control key is pressed in combination with other keys to initiate commands as specified by the software.

alt-keyThe Alternate key is also used in combination with other keys to initiate commands.

key-Backspacethe Backspace is used to delete a character to the left of the cursor, moving the cursor back one position. The cursor is the flashing indicator on the screen that shows where the next character will be inserted.

enter-keyThe Enter key moves the cursor to the beginning of the next line. For instance it is used at the end of a paragraph.

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