Define the terms user interface. Distinguish between a command line interface and a graphical user interface?

User Interface: 
A user interface is combination of hardware and software that you use to communicate with and control the computer. Through the user interface, you are able to make selections the computer, request information from the computer and respond to message displayed the computer. Thus, a user interface provides the means for dialog between you and the computer.

The two broad categories of user interface supported by various operating systems are:

1. Command Line Interface
2. Graphical user interface(GUI)

Command Line Interface

1. In command line interface, the user give instruction to the computer by typing commands. 
2. They use less RAM and secondary storage capacity. 
3. They do not require graphics display. 
4. It execute the command very fast. 
5. Simple task can be performed easily. 

Graphical User Interface

1. Instead of typing command, selection is achieved by moving a pointer with a mouse and clicking a mouse button. 
2. They use more RAM and secondary storage capacity. 
3. They require a more powerful processor and a better graphical display. 
4. They are slower when executing a command because a much more interpretation takes place. 
5. They can be irritating to use for simple task because a greater number of operations is required.