GCSE A* REVISION NOTES


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Software

Explain the need for the following functions of an operating system: user interface, memory management, peripheral management, multi-tasking and security

Memory Management

The operating system controls the memory of the computer by loading programs into memory when started and providing the processor with the address of the start of it. It also keeps track of the programs and data using address

Multi-tasking

The operating system allows multiple programs to be run at the same time and makes sure that each one gets enough processor power giving priority to more important processes. Processes are designated running for the current process, runnable if they can be attended to next and waiting if they must wait for the signal that sets them to runnable,

Peripheral Management

Peripherals – Any component outside of the process and memory

The operating system has to manage these and make sure they work with optimal efficiency. An example of this is using buffers to ensure that data is not lost when outputting or storing data to slower peripherals. Device drivers are written to allow the operating system to interact with each peripheral. When a device is required an interrupt code is sent to the CPU switching its attention. The device drivers are different on every operating system as they have different interrupt codes. Most operating systems provide the ability to fine tune peripherals such as control panel.

Security

The operating system protects processes from each other by dividing memory into pages and recording which process is using which pages to avoid conflicts. It also marks files with the privileges each user has regarding it to prevent unauthorised access to data.

User Interface

Command Line

This allows greater customisation of the operating system and makes administering a network less of an effort.

Graphical User Interfaces (GUI)

These reduce the need to learn commands but are less easily customisable

Describe the purpose and use of common utility programs for computer security (antivirus, spyware protection and firewalls), disk organisation (formatting, file transfer, and defragmentation), and system maintenance (system information and diagnosis, system cleanup tools, automatic updating)

Security

Antivirus Software

This prevents harmful programs being installed on the computer, prevents important files such as the operating system, being changed or deleted. If a virus does manage to install itself the software will detect it when it performs regular scans. Any virus detected will be removed (inoculated). New viruses are found regularly so it is important that any antivirus software gets regular updates.

Firewall

Restrict outgoing and incoming access to certain network addresses. This prevents hackers from infiltrating the network but can also be used to restrict access for certain users (e.g. blocking games for students).

File Management

Windows explorer and other utilities provide a logical view of how the files are organised to make it easier for the user

Disk defragmentation tool

After a while files on a hard drive disk become fragmented from the deletion of data and insertion of new data wherever there is space. This means that files get broken up and written to the disk in bits which makes it slower to read and open the file. A disk defragmenter improves the efficiency of the computer by moving separate parts of the files around so they can be stored together making it quicker to access them. It also groups all the free space together so any new files can be stored  in one place.

 Maintenance

System information and diagnosis

Utility usually provided by the operating system that gives information about the hardware, statistics about its use and information that will help diagnosis problems with the computer.

System clean-up tools

Searches for and removes files that are no longer needed. This will free up disk space, speed up how quickly the system boots and improve performance.

Automatic Updating

Makes sure any software installed on the computer is up to date by regularly checking the internet for updates.

Discuss the relative merits of custom written, off the shelf, open source and proprietary software.

Open source

Pros:

Cons:

Proprietary

Pros:

 Cons:

Off-the-shelf

Pros:

Cons:

Custom-written

Pros:

Cons:


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