1. Lesson Objectives Aims You should be able to:
Understand the function and purpose of an operating system including:
User Interfaces
Memory Management
Multitasking
Peripheral Management
Drivers
User Management
File Management

2. What is a computer? A collection of hardware
Made by many different manufacturers…
…with different specifications and capabilities
It’s actually a bit of a nightmare.

3. Computers these days are general purpose and we expect to be able to:
It gets worse
Computers these days are general purpose and we expect to be able to:
Plug in any device we like…
…From any manufacturer
Install any application we need
Interact with networks and the internet
Use new things when they come out (that don’t even exist yet!)

4. Why does it all work?
Something has to connect all this hardware and software together and make it:
Behave
Talk to other components
Let you use it in a nice, friendly way (it’s pretty desolate and scary in hardware land)
That something is…. Software!
But a very special piece of software – an Operating System

5. An operating system
Hardware
Kernel
Drivers
Interface

6. Operating System An Operating System is: Software
Which controls and manages ALL hardware in a computer system
Provides a platform for software to run on
Provides a user interface
Encapsulates hardware and its workings to abstract these from the user (makes it so you don’t have to worry about how hardware works or what it’s doing)

7. Lets break it down
We need to go in to detail, to do this we will look at 3 distinct sections:
Hardware and resource management
User Interfaces
User and file management

8. Hardware and resource management

9. Examples of resources are:
Any hardware in your computer is a “resource” – something that can be used.
Examples of resources are:
CPU time
Memory (space/allocation)
Storage

10. Resources
The operating system Kernel is responsible for allocating these resources:
How much time can a task use the CPU for?
Which program should run next?
How much memory is a program allowed to use?
Where in storage should that file go that you just saved?

11. Multi Tasking Let’s establish some facts:
1 core (CPU) can ONLY perform ONE task at a time.
Yet we appear to be doing lots of things at once on a PC
This is because of a trick called time sharing where we flick between tasks really quickly to give the APPEARANCE they are happening at the same time

12. Multi-Tasking
Running (or appearing to run) more than one task at any one time
Each core will run one task each at any one time
If more tasks are running then the operating system will share the time each core spends on a task so it appears each task is running simultaneously

13. Memory Management
Multi tasking requires the operating system to manage the memory
Memory is split up into segments or pages
These pages can then be allocated to programs as necessary

14. The clever thing here is that a program:
Doesn’t have to be all together in RAM
Can be moved around by the operating system
Cannot interfere with other running programs
Can be swapped in and out of physical memory if necessary
The operating system will ensure that each program goes in its own space in memory

15. Drivers and Peripherals
As we saw previously, a computer is a collection of hardware
All of which will work in different ways
Even devices of the same type – two different SSD manufacturers will use different techniques for storing and organising data

16. Drivers
To make peripherals work, they require a driver
A driver is a piece of software which sits between the device and the OS
It is like an interpreter…

17. Drivers
Drivers will receive “calls” from the OS – “print a page” for example
It is up to the driver to work out HOW that happens and to control the specific piece of hardware it is designed for
This means an OS does not need to try and include code for EVERY device ever made
Manufacturers must provide these driver files so their hardware works on your computer!

18. User Interfaces

19. What is an interface?
You cannot physically interact with the components of a computer
Can you put a byte in memory? Can you ask the CPU to perform a task for you?
No… so how do we tell a computer what to do and see what it’s doing?

20. Interface
An interface is how we interact with a computer
It usually consists of some hardware (keyboard, mouse, screen) and some software.
Our focus here is on the types of software interface that are common

21. CLI
In 1982 if you turned your new £500 computer on, this is what you’d see:

22. And later in 1990 if you spent £3000 on a top of the range, super fast 386 20mhz beast:

23. How does it work? You can perform all computing tasks using commands
These are short words or abbreviations that perform a specific task such as:

24. Command Line
The CLI is powerful and can do many things that are difficult through a GUI:
Switches
Piped output
Batch/Script files

25. Can perform tasks not possible in a GUI
Advantages
CLI interfaces do not require powerful hardware to run or use many system resources
Suitable for embedded systems
Low power systems
Administrator/power users
Can perform tasks not possible in a GUI
Batch or scripts to set up users for example

26. Disadvantages Not intuitive
Novice or new users would find it difficult to use
Error messages can be short and unhelpful
Complex learning curve
Not obvious how to use it at first

27. GUI = Graphical User Interface
Meaning it uses images to help the user understand what’s going on
You have used these your whole life

28. Generally we describe a GUI as having four main components:
Components of a GUI
Generally we describe a GUI as having four main components:
Windows
Icons
Menus
Pointer
You need to be able to describe each and what it allows a user to do.

29. GUI’s allow us to visually:
Uses of a GUI
GUI’s allow us to visually:
Multi task
Load programs
Organise user areas
Organise a file system
Install and use programs
Launch and interact with programs

30. Advantages and Disadvantages
Intuitive / user friendly
Visual cues make it easy for users to work out how to use the system
Visual representation of real world objects (a bin icon for the recycle bin for example)
It’s natural to “point” at things you want and to drag and drop
Uses a lot of system resources
Memory, graphics RAM/GPU time, CPU time
Not suited to repetitive tasks

31. Menu Driven/Voice Controlled
Some OS’s use a purely menu driven interface for all interactions
Or voice controlled
Alexa
Google Home
Siri

32. User and File Management

33. File Management
A hard drive or SSD is literally just a massive box you can put data in
How that’s organised is up to you! Or the OS at least
The way an OS organises this space is called a File System
FAT32
NTFS
APPLEFS
EXT4

34. File Systems
There are lots of ways a file system can organise the space and each has advantages and disadvantages such as:
Security (encrypted or not?)
Redundancy (is there any kind of error recovery in the file system?)
Error checking
Method of file access
Fragmentation control
How efficiently space is used/allocated

35. User Management An operating system may be:
Single User
Multi User
OS’s like Unix, Linux, OSX are based on multi user code
Users normally:
Have their own area for personal storage
Can have access to files/folders and programs as directed by an administrator
Can be added to groups which affect what they see and can do on a system