1. Ch 26 & 27
User Interfaces

2. Objectives:
Identify operating systems, including those which contain a:
graphical user interface (GUI),
command-line interface
Be able to describe the features, advantages and disadvantages of the different types of user interface

3. Purpose of an operating system:
To recap, two of the purposes of an operating system are:
To provide a user interface so that we can interact with the computer
To manage applications that are running on the computer, starting them when the user requests, and stopping them when they are no longer needed

4. User Interfaces What is a user interface?
The system that people use to interact with a computer (to give it commands, to see the results of those commands, etc.) is known as the user interface.
There are two that you need to be aware of:
Graphical User Interface (GUI)
Command-Line Interface (CLI)

5. Graphical User Interface (GUI)
A GUI is an interface built around visual (graphical) things.

6. GUIs
The GUI allows the user to interact with the computer using pictures or symbols (icons).
The mouse controls a cursor, which is used to select icons to open/run windows, or to select menu items.
Each window contains an application.
Modern computers allow several windows (applications) to be open at the same time.

7. New GUI technologies
Modern devices (eg touch screen phones) use post-WIMP interactions, where users’ fingers are in contact with the screen
This allows newly developed actions such as pinching and rotating, which would be difficult with a single mouse pointer.

8. Graphical User Interface (GUI)
The most common technology used by GUIs to provide a user interface is WIMP.

9. Windows
regions of the screen used to display information

10. Icons
small pictures that are used to represent folders, software, etc.

11. Menus
lists of options the user can select from

12. Pointers
A pointer is an arrow that can be moved around the screen and is used to select things

13. GUIs Windows is an example of an operating system with a GUI.
GUIs are quite easy to use due to the visual nature of the interface – the user has lots of visual clues as to what things do.

14. BUT
displaying all of the graphics required by a GUI takes a lot of computing power so quite a powerful computer is needed, and a lot of RAM.

15. Advantages
Easier to use than a command line interface, as the icons are images that represent the functions
No special training is required: the user can usually work out what clicking on an icon will result in: it’s an intuitive system

16. Disadvantages
Icons are image files, and therefore take up a lot of space both in the memory (RAM) and the backing storage (hard disk)
This means that a modern GUI such as Windows 7 may need 2GB of RAM to be able to function properly
If a computer is older, using a GUI could be a very slow process

17. Command Line Interface (CLI)
Many years ago when computers were not very powerful they could not display the colourful graphics required for a GUI. The only interface available to most computer uses was the ‘command line’.

18. Command Line Interface (CLI)
The user would see nothing but a black screen. They would have to type a command to make anything happen. e.g. To copy a text file called NOTES from a floppy disc to the hard drive the user would have to type: > COPY A:\NOTES.TXT C:\

19. Command Line Interface (CLI)
The user would have to learn a whole set of strange commands so that they could make use of the computer system. Plus it was not very interesting to look at – no visual clues to tell you what to do next. This meant computers used to be quite difficult to use, so this type of interface is only really suitable for expert users.

20. Command Line Interface (CLI)
Command-line interfaces are still used today on many servers. These computers need to use all of their computing power running networks, etc. so they do not use GUIs.

21. Command Line Interface (CLI)
They take up much less RAM and processing power than GUIs, and are much faster to use (if you know what you’re doing!)

22. Try it:
Use this link to see how to write the command to copy a file (using DOS) – you have to type in where the file is that you want to copy, and then type in where you want to move it to (so you can imagine how much longer it would take you than simply clicking on an icon):

23. Advantages
Command line interfaces don’t contain any RAM-hungry graphics files, so they don’t require very much memory or storage
If the user is an experienced programmer, this is the fastest user interface to use: no need to open up a succession of windows in order to find the correct file

24. Disadvantages
If you don’t know the correct commands, it could be impossible to use!
A ‘normal’ computer user would find it very slow – there are many commands to learn
A simple typo would mean that a command could not be executed
It is not as intuitive as a GUI

25. Menu-driven Interfaces
This is a type of interface still used in some mobile phone applications
The user selects what he or she wants to do from a succession of menus
Each menu has several sub menus, and each sub menu has further sub menus

26. Advantages
No icons or images, so don’t require as much RAM or processing power as GUIs
No knowledge of coding necessary, so easier to use than CLIs.

27. Disadvantages
Slower to use than a GUI, as the user has to navigate through a number of menus and submenus before he is able to find what he wants.
Cannot click on an icon to open a specified file or folder.
Much slower to use than a CLI, and uses more memory too