External I/O Devices

External I/O Devices:
There are three categories of external devices;
i) Human readable
o  Suitable to communicate with the computer users
o  Screen, printer, keyboard

ii) Machine readable
o  Suitable to communicate with the equipment
o  Monitoring and control
o  Magnetic disk and tape systems, sensors and actuators

iii) Communication
o  Suitable for communicating with remote devices such as terminal, a machine readable device or another computer
o  Modem
o  Network interface card(NC)


Keyboard/Monitor:
·      These are the most common means of computer/user interaction.
·       The user provides input via the keyboard and the monitor displays the output.
·       The basic unit of exchange is character. Associated with each character is a code, typically 7 or 8 bits in length.
·       Each character in this code is represented by a unique 7-bit binary code.
·       Characters are of two types; printable and control characters. Printable characters are the alphabetic, numeric and special characters that can be printed on the paper or displayed on a screen.
·       Control characters do with the controlling of the printing or displaying of characters.

Figure 7.2

The nature of an external device is indicated in Figure 7.2. The interface to the I/O module is in the form of control, data, and status signals.