1. Software - Operating Systems
Year 11 Computer Science
Software - Operating Systems

2. Operating Systems - Starter Activity
Windows 10 is an example of an Operating System. What other “OS’s” can you think of?
What do all Operating Systems have in common?
Which is the best Operating System, in your opinion?

3. Operating Systems
Mac OS X
Linux
Windows
Android
iOS

4. Computer Systems - Hardware and Software
Computer Systems consist of both hardware and software.
Software is the set of programs that run on a computer system. There are two types of software:
System Software
Application Software
These are “apps” or programs that do particular jobs for us, such as:
Microsoft Word (to create documents)
iTunes (allows us to play music)
IDLE (allows us to create Python programs)
This is software that enables us to use the computer and application software, by providing a user interface and tools to manage the hardware.
This includes Operating Systems and Utility software, such as Antivirus software

5. What is an Operating System?
The Operating System (or ‘OS’) is the main software that controls the general operation of a computer, and provides an easy way for us to interact with computers and run applications.
Examples include Microsoft Windows 10, Microsoft Windows 7, Mac OS, and LINUX, which are all used on computers.
Android and iOS are examples of operating systems used on SmartPhones.

6. What are the main functions of an Operating System?
The main functions of an operating system include:
User interface - provides a user interface so it is easy for users interact with the computer
multi-tasking - allows multiple applications to run at the same time via a process called scheduling
memory management - transfers programs into and out of memory, allocates free space between programs
provides device drivers - which allow a computer to communicate with peripheral devices, such as a printer.
organises - creates a file system to organise files and directories
security - provides security through user accounts and passwords

7. User Interfaces
An important feature of Operating Systems is to provide a user interface for the user to interact with the computer.
A GUI (Graphical User Interface) is the most common type of interface and provides windows, icons, menus and pointers (WIMP)

8. GUI – Graphical User Interface
A GUI (Graphical User Interface) is the most common type of interface and provides windows, icons, menus and pointers (WIMP)

9. CLI – Command Line Interface
A command line interface (CLI) uses text based commands to carry out tasks.
They are difficult to use as they require the user to know a range of commands.
They are generally intended for expert users.
They are extremely fast as they do not require much processing power.

10. Multi-Tasking / Scheduling
Multitasking is where you have more than one program open and running at the same time.
They are not really running at the same time, the processor is allocating a small amount of time to each process.
This happens so quickly, it feels as if they are running simultaneously.

11. Multitasking / Scheduling
The processor is actually executing instructions from each of these applications one after the other.
It is happening so quickly, that it appears that they are running simultaneously. This is known as scheduling.
Word
Chrome
Spotify
The CPU is switching between applications over time

12. Multitasking – Scheduling (2)
Effectively, there is a queue of processes that are waiting to be executed by the processor.
The Operating system switches between processes (applications).
The Operating System can prioritize particular processes over another.
Word
Chrome
Spotify
The CPU is switching between applications over time

13. Memory Management
The operating system also has to manage memory (RAM) carefully.
When a program is loaded from the hard disk, the Operating System puts into a specific place in the RAM for access by the CPU.
The Operating system will remove any programs that the user closes from memory locations in RAM.

14. What happens when memory (RAM) is full?
When memory is full (due to too many applications being open at the same time), the Operating system has a trick up its sleeve.
It creates a section of  virtual memory (virtual RAM) on your storage device (such as a hard drive).
This means a section of your hard drive is used as RAM!
This is known as virtual memory.
CPU
RAM
Hard Drive

15. What happens when memory (RAM) is full?
A process called swapping/paging is the process the OS uses to move data between RAM and virtual memory.
The OS moves data from processes that are not immediately needed out of the RAM and stores them in virtual memory. It copies the data back into RAM when the process is needed again.
Using virtual memory slows the computer down because copying to a hard disk takes much longer than reading and writing RAM.
CPU
RAM
Hard Drive

16. Device Drivers The Operating System provides device drivers.
Device drivers are small pieces of software that allow peripheral devices, such as printers to communicate with your computer.
They translate OS instructions into commands that peripheral devices actually understand.

17. Device Drivers

18. User Management
Operating systems allow for different users to log into a computer with their own usernames and passwords.
The OS will retain individual settings for each user, such as their icons, desktop backgrounds.
Each user may have different access rights to files and programs.

19. File Management
The Operating system provides a logical structure for file management.
This means files can be organized into folders, and users can rename, delete or copy and move files around easily.