1.3 Operating Systems

The operating system is a crucial piece of system software that manages the computer's resources and provides services for application programs.

The operating system is responsible for several critical tasks:

• Dealing with errors that occur in applications programs
• Maintaining security of the whole computer system
• Maintaining a computer log which contains details of computer usage
• Allowing communication between user and the computer system (user interface)

User Interface is the means by which the user and a computer system interact, in particular the use of input devices and software.

There are two main types of user interfaces:

• Command Line Interfaces (CLIs)
• Graphical User Interfaces (GUIs)

A Command Line Interface (CLI) is a type of interface where the user types in specific instructions to perform tasks.

CLIs require a user to type in instructions in order to:

• Choose options from menus
• Open software
• Execute various operations

There are often a number of commands that need to be typed in, for example, to save or load a file. The user therefore has to learn a number of commands just to carry out basic operations.

Consider the task of importing data into a table called B. Using CLI, the code would look like this:

1. SQLPrepare(hStmt,
2.   (SQLCHAR *) "INSERT INTO tableB SELECT * FROM tableA",
3.   SQL_NTS):
4.   SQLExecute(hStmt);

This example shows how complex it is just to carry out a fairly straightforward operation using CLI.