OPERATING SYSTEMS

S.NEEBAR

Functions of an Operating System,

Memory management

Device input and output management

Security control

Program management

File management

Logging events

Memory management

An operating system manages memory by allocating memory to programs that need it. It also removes programs from memory when they are not being used.

Device and I/O management

The operating system is an essential interface between applications and hardware components of a computer. For example the operating system will allow a word processing application to connect to a printer to print a hardcopy of a document. The operating system controls the flow of data from input devices to the processor and sends the data to the appropriate output devices when needed.

Security Control Confidential information stored on computers may be at risk in organisations where there are many computer users. Operating systems provide security features that require to log on to a system using a username and a password.

Operating systems keep track of users that log on to a system. They record the amount of time they use the computer and what resources they accessed. A computer administrator can access this data

Program Management

The operating system will launch a program when you tell it to. It will abort programs that are not working properly

File Management

The operating system keeps track of all files in a computer. It locates and retrieves stored files and saves files to memory when you tell it to. The operating system allows you to copy, erase, rename and back up files.

Logging of Events

The operating system keeps a log of all tasks that were executed on the computer. These logs are useful for spotting and diagnosing problems and to monitor users .

Managing Processes & Tasks

The computer manages many processes and task at the same time. To make the computer faster and more efficient and multifunctional the computer may implement the following:

Multitasking

Multiprocessing

Multiprogramming

Multitasking This is when one processor performs several tasks at the same time.

Multitasking involves performing multiple tasks in parallel. Usually, CPU processes only one task at a time but the switching of CPU between the processes (also known as Context Switching) is so fast that it looks like the CPU(or processor) is executing multiple processes at a time. Example of multitasking, we listen to music and do internet browsing at the same time (they execute in parallel).

Multiprocessing This is when two or more processors run one program.

Multiprocessing is a method of computing in which different parts of a task are distributed between two or more similar central processing units, allowing the computer to complete operations more quickly and to handle larger, more complex procedures.

Multiprogramming Multiprogramming is when one processor runs more than one program at the same time.

Multiprogramming is basically a type of parallel processing that can be used in many different environments. It makes it possible for a few programs to work at the same time. In multiprogramming, more than one program lies in the memory i.e. in terms of operating system, the scheduler selects the jobs to be placed in ready queue from a number of programs. The ready queue is placed in memory and the existence of more than one program in main memory is known as multiprogramming.

Multiprogramming continued

Example of multiprogramming, we open word, excel, access and other applications together but while we type in word other applications such as excel and access are just present in main memory but they are not performing any task or work. Or we can say that are not being used at the same time.

Multiprogramming

Processing Modes

Data can be processed in four ways :

Batch processing

Online processing

Real-time processing

Time sharing

Batch processing

Batch processing is when a number of transactions or jobs are processed in one go and require little or no user intervention. An example of this are when utility companies generate bills for their customers.

Online processing

Online processing requires the computer to be online. As soon as the transaction or job occurs the data is processed immediately or is stored and processed a short time later. For example if you pay using a credit card at a supermarket the transaction will be recorded immediately but it may take a few hours before it appears on your account

Real-time Processing

Real-time processing is just that, processing calculations right now, in real time. Tasks are processed as they come in, on a first come, first served basis.

Time Sharing

In time sharing, the operating systems shares the time between the tasks. If the OS is given two tasks to perform, it performs the first job for a predefined time, and then takes up the next job for the same time, continuously switching tasks until they are complete. This way the OS shares its time between all the jobs arriving.

User Interfaces

The system that people use to interact with a computer (to give it commands, to see the results of those commands, etc.) is known as the user interface. The main software user interfaces are:

•Command-Line Interface (CLI)

•Graphical User Interface (GUI)

Command line interface Many years ago when computers were not very powerful they could not display the colourful graphics required for a GUI. The only interface available to most computer uses was the ‘command line’. The user would see nothing but a black screen. They would have to type a command to make anything happen. The user would have to learn a whole set of strange commands so that they could make use of the computer system. Plus it was not very interesting look at; no visual clues to tell you what to do next. This meant computers used to be quite difficult to use. In expert hands however, the command line is a powerful tool to interface with the computer.

Graphical user interface A GUI is an interface built around visual (graphical) things:

• Commands are issued by clicking on icons

• Icons are small pictures that are used to represent folders, software, etc.

• Menus are lists of options the user can select from.

Windows 10 is an example of an operating system with a GUI. GUIs are quite easy to use due to the visual nature of the interface – the user has lots of visual clues as to what things do. However, to display all of the nice graphics required by a GUI takes a lot of computing power so a more powerful computer is needed.

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