6.1: Operating Systems
Eduqas / WJEC
What is an Operating System?
An operating system (OS) is software that helps to manage the resources of a computer system.
There are eight main roles of an operating system:
Manage the CPU
A critical role of the OS is to manage the CPU so that applications and processes can be run efficiently.
The CPU is effectively managed by performing three further roles:
Manage Memory (RAM)
The OS reserves memory space in RAM for stored programs to be copied into. The FDE cycle is executed continuously to carry out the instructions.
The OS also ensures that programs are appropriately managed so that data is stored in correct memory locations and not corrupted.
A interrupt is an alert signal sent to the CPU when an application or hardware device requires immediate attention.
The OS must efficiently manage interrupts so that a problem can be dealt with quickly if one occurs.
The OS manages tasks so instructions can be executed by the CPU in turn - this is called scheduling.
The OS prevents processes from interfering with others and crashing. Tasks should appear to run simultaneously even though only one process can be executed at a time.
The backing store is another term for secondary storage devices such as the magnetic hard disk drive, optical drives or solid state memory sticks.
The OS ensures data is stored correctly and can be efficiently retrieved from the backing store. Files are organised in a hierarchical (logical) structure.
A peripheral is an external device connected to a computer system to input or output data.
The OS manages the receiving of data from input devices (such as a keyboard or mouse) and the transfer of data to output devices (such as a monitor or speaker).
The OS allows users to create, manage and delete accounts with different permissions. It also permits multiple users to log in and change passwords.
Antivirus and firewall software is managed by the OS as well as some data encryption processes.
Manage the User Interface
The final function of an operating system is to provide a user interface. The most common type of user interface is a graphical user interface (GUI) which can be presented in the following ways:
Icons are displayed to represent shortcuts to applications and files.
Multiple windows can be opened at the same time and switched between.
A folder and file system is displayed and manipulated allowing for copying, searching, sorting and deleting data.
The interface can be customised, such as changing font sizes and the desktop background.
The taskbar allows shortcuts to be pinned for quick access.
Menus can be opened from the Start button to display files and shortcuts.
System settings can be accessed such as network and hardware options.
Other types of user interface do exist, such as a command-line interface (CLI). This type of interface is entirely text-based and requires users to interact with the system by typing commands. This is a complicated process and mistakes could easily accidentally delete data. There are many commands to learn so only experts who have been trained to learn this interface will be able to efficiently make use of it.
6.1 - Operating Systems:
1. Describe each role of the operating system:
1. Manage the CPU 
2. Manage memory 
3. Manage interrupts 
4. Manage multi-tasking 
5. Manage backing store 
6. Manage peripherals 
7. Manage security 
8. Manage the user interface 
2. Describe 5 different ways the operating system can provide a user interface.