Computer Science Unit 2 - Operating Systems


Role of Operating Systems

An operating system is used to manage the complexities of hardware from the user. The operating system manages hardware resources in order to provide an orderly and controlled allocation of resources to the various applications competing for those resources.

In short:

- Manages complexities of hardware

- Manages hardware resources to applications

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Modes of Operation

Single-user, Single Task 

Only one user using the device accessing one item at a time. There are not many of these operating system available now old mobile phones or old MSDOS based systems 

Single user Multi-Tasking 

Windows and Linux are examples of this, with multiple things happening at once, printing whilst writing a document 

Multi user, Multi-Tasking 

Multiple users carrying out a large number of tasks at once, Windows Server edition and UNIX is an example of this.

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Managing Resources

The OS manages the resources of it's hardware which commonly includes a processor, RAM, backing store and input/output devices. All these devices are used in different ways.


The processor manages memory read/write, control signals, scheduling while the OS ensures that those tasks appear to run simultaneously. The processor also ensures that program don't interfere with each other and crash. The OS also manages interrupts.


The operating system will manage operations memory read or write. The OS also makes sure that all data stored in memory is in the correct address in memory and keeping track of free memory locations. In the cases where virtual memory is needed, the OS will manage it. The OS also insures that data stored does not overlap and memory space is allocated appropriatley in memory.

Backing Store

The OS makes sure data can be retrived from any disk drive and creates and maintains a filing system of blocks and organised into a hierarchical directory structure.

Input / Ouput Devices

The OS will manage any data received and interpret it. The OS also manages data being outputed to the correct peripheral at the correct time.

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OS Interface

An operating system will give the user an interface to be able to interact with the OS more easily. There are three types of interfaces that an operating system can provide.

Command Line Interface (CLI)

A CLI is an interface that allows a user, who has knowledge of the commands, to navigate an operating system with text commands entered. This uses far less resources because of the minimal graphics. Requires training or educating on the command functions but are effeicent and are used commonly in server operating systems.

Graphical User Interface (GUI)

A GUI is an interface that allows a user to easily navigate an OS, without prior training. Most PCs use GUI because of the ease of use to reagular users.

Menu Based Interface

A menu based interface shows the user preset text based menus for the user to select. This is commonly used in an OS to allow a user to change settings in the BIOS.

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Managing Backing Store

The operating system manages the backing store through the use of a hierachical directory structure. A hierarchical directory structure allows a user to locate files by navigating logically linked directories while allowing the physical location of the file can be anywhere on the disk. The File Allocation Table (FAT) is a system that keeps track of physical locations on a disk are for each file.

hierarchy structure

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File Attributes

The attributes of a file are settings associated with that file which can allow or deny access to reading the file, writing over the file or listing the file in the user directory.

file attributes

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Choice of OS

A company wanting an OS for their many employees PC would want a relatively cheap OS to save cost when an OS on mass. Although, a company would most likely pay more for a one-off purchase of a client server OS.

A graphics design company would want an OS that is compatible with their software needed for work. Whereas, a small retail shop would only need their OS to be compatible with very common software for such things as calculating and storing finance information.

Customisation requirements
An individual user wanting a PC for leisure would most likely want an OS that can be customized visually, such as backgrounds or cursor icons. Where as, a PC for work wouldn’t necessarily need lots of customization and would benefit from simplicity.

If a national banking company wanting an OS for their server they would want it to be able to perform with speed when handling multiple users. Whereas a small blog run by one person could do with minimal performance.

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Utility and Application Software


Utility software is system software used to help optimise, analyse, configure or maintain a computer. I.e. software that does not to take for the user but the hardware/system. Utility software would include disk defragging software, anti-viruses software and disk compression software.


Application software is a software used by the user for everyday things such as entertainment or work. Application software would include Microsoft Office, Steam, web browsers.

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