1. LO2 – Understand Computer Software
2.4 – Operating Systems

2. Operating System In any computer, the operating system:
Controls the backing store and peripherals (hardware) such as scanners and printers.
Deals with the transfer of programs in and out of memory.
Organises the use of memory between programs.
Organises processing time between programs and users.
Maintains security and access rights of users.
Deals with errors and user instructions.
Allows the user to save files to a backing store.
Provides the interface between the user and the computer - for example, Windows Vista and Apple OSX. For more information, see the User Interfaces study guide.
An operating system is the core software that allows a computer to run as a useful device. It manages the hardware, the user interface and all other software running on the computer. Without an operating system, a computer is just a collection of components heating up the room as no-one would be able to make any practical use of the machine.
A large number of operating systems have been developed over the years; each designed with a certain kind of computer in mind:
Windows or Linux for personal computers
MacOS for Macs
Unix for mainframes
Symbian, Android for mobile phones

3. Operating System Single User Operating Systems
Single user operating systems can be split into two types:
Single User – multi-tasking
Found on a personal computer. The operating system is designed mainly with a single user in mind, but it can deal with many applications running at the same time; e.g. you might be writing an essay while searching the Internet, downloading a video file and also listening to a piece of music.
Example operating system include:
Windows
Linux
Mac OS X
The difference compared to the Single-user, Single application system is that it must now handle many different applications all running at the same time. The memory available is also very different, for example it is quite normal to have Gigabytes of RAM available on a personal computer which is what allows so many applications to run.
Single User – single application
This type of operating system only has to deal with one person at a time, running one user application at a time e.g. found on a mobile phone. There can only be one user using the mobile and that person is only using one of its applications at a time.

4. Operating System cont…..
Multi user, multi tasking operating system
Personal computers can multi-task very well when you want to do tasks like reading s, writing letters, working on spreadsheets, listening to music, surfing the web, watching videos etc
However some times only a really powerful computer will do the job, for example:
You are an engineer or scientist and want to run a very complicated simulation
You are a weather scientist and want to run a forecast
You are a financial person and want to work on thousands of stock market share movements
You work in a bank and want ot handle customer accounts
You are an architect and want to see your full design
You work at a University as an academic along with hundreds of other academics
You are a film animator and want to work in 3D
Most computers can’t handle these kind of tasks. Instead, a mainframe or supercomputer is required for this kind of work.
But there is a problem. A supercomputer or mainframe costs millions to buy and maintain. There is no way that such an expensive machine could be used by just a single person. To make it economic, this computer has to be shared. This means it needs a multi-user operating system which means more than one user is logged on and can use the computer at the same time. Each person needs to be able to run more than one application at a time, so it needs to be multi-tasking as well.

5. Operating System cont…..
Network operating system
All machines on a network of computers need to have an operating system that can deal with the network.
Examples of network operating system include; Windows and Mac OS X and all the mainframe operating systems
A network operating system has to have the following features:
Deal with users logging on
Maintain the network connection to the server(s)
Expand the file system to view folder on other computers
Provide security to separate user accounts from each other
Single Processor systems have only a single processor or CPU, which is shared between users by dividing the CPU time into time-slices and allocating one of these to each user in turn.
Most systems use single processor systems.
They perform only one process at a given time, and it carries out the next process in the queue only after the current process is completed.
OS monitors the status of them and also sends them next executable instruction.
It relieves CPU of disk scheduling and other tasks.
It is suitable for general purpose computers , as it cannot run multiple processes in parallel.
Multi Processor System Also known as parallel or tightly coupled systems as they can run multiple process in parallel to each other efficiently. Two or more processors will be in close communication with each other with shared memory, storage and power supply.
In these days rather than using multi processor systems, people tend to buy single processor with multiple cores. This can be more efficient as internal on-chip communication is faster than communication between different processors.
Multi-core processors also use less power than that of multiple single core processors.
Advantages
Increased throughput - As there are a number of processors, more work can be done in less time. These multiple processors run parallel to each other increasing the performance of the system.
Reliability and failure-free - Failure of any processor will not affect the functionality of the system, as there are a number of processors. We can expect failure free service from multi-processor system.
Economy of scale - Multi Processor Systems cost less than a number of individual single processor system. In the case of multi processor system expenditure for system cabinet, memory power supply, accessories are saved as these systems share resources like power supply, memory and also space