The different types of operating system used in the computer
(i) Single User and Single Task Operating System
(ii) Multi User Operating System
(iii) Multi Processing Operating System
(iv) Distributed Operating System
(v) Prominent Operating System

The Operating System provides three levels of securities to the user end. They are
(i) File access level
(ii) System level
(iii) Network level.

(i) Controlling input and output devices.
(ii) Managing computer resources such as Central Processing Unit, memory, Disk drives and printers.
(iii) Executing and providing services for application software.
(iv) Establishing a user interface.

(i) Multiprocessing is the use of two or more CPUs within a single computer system.
(ii) A system is said to be multiprocessing if it has more than one physical processors. Since it has multiple processors available, multiple processes can be executed at a time.
(iii) In Multiprocessing, processes can be assigned to a different processor for its execution.
(iv) With the help of multiprocessing system more work can be done in a shorter period of time.
(v) Multiprocessing system provides increased reliability means that if one processor fails, the other processor will continue its working. For example, if there are10 processors and 1 fails then the work does not halt, instead the remaining 9 processor will share the work of 10 th processor.
(vi) Multiprocessing system increases the Throughput i.e. if we increase the number of processors, more work can be completed.
(vii) As multiprocessing occurs by parallel processing, it is cost saving since it parallelly shares memory, buses, peripherals, etc.
(viii) Multiprocessor refers to hardware (CPU units) rather than software (running programs).

User interface:
(i) It is one of the important features of an Operating system.
(ii) User interface allows user to interact with computer effectively.
(iii) An interactive Operating system provides astonishing feature of Graphical User Interface.
(iv) GUI is one of the advanced features that have made Windows and other interactive Operating system highly popular.
(v) Some properties of GUI are display of icons, movement of cursor, etc.
Memory Management:
(i) Operating system performs the function of memory management. Memory Management is the process of controlling and coordinating with computers main memory.
(ii) The Operating system keeps a track of main memory/primary memory i.e. which portion of memory is currently being used and who is using them.
(iii) Memory Management involves allocation and de-allocation of memory blocks.
File Management:
(i) File Management is an important function of Operating System that maintains and manages file operation.
(ii) File Management manages files, folder and directory system on computer.
(iii) The process of File Management includes creating, modifying and deleting of files.
(iv) File Management of Operating system helps to create new files and place them at specific location and makes the process of sharing of files easy.
Process Management:
(i) Process Management includes creation and deletion of processes.
(ii) Process Management provides mechanism for communication and synchronization of processes.
I/O Management:
(i) The Operating system is responsible for all sorts of input from keyboard, mouse, desktop, etc.
(ii) Operating system effectively handle I/O operation to hide the peculiar behavior from the end-user.
Security Management:
(i) Operating system provides security by protecting unauthorize access to computer and uses password and other similar technique to protect user data

Time-Sharing Operating Systems
Advantages	Disadvantages
Provides the advantage of quick response.	Problem of reliability.
Avoids duplication of software.	Questions of security and integrity of uses programs and data
Reduces CPU idle time.	Problem of data communication.

(i) Process is a program that is under execution.
(ii) Process Management is the job of Operating System to manage all the running processes of the system.
(iii) Process Management algorithms are
1. FIFO
2. SJF
3. Round Robin
(a) FIFO:
1. First In First Out (FIFO) is the simplest process algorithm.
2. FIFO simply queues the processes in the order of their arrival.
3. For example, a student is standing in a queue to get grade sheet from his/her teacher. The other student who stands first in the queue get his/her grade sheet first and leaves from the queue, followed by the next student in the queue gets it corrected and so on.
4. Technically the process that enters first in the queue is executed first by the CPU, followed by next and so on.
(b) SJF:
1. Shortest Job First (SJF) is an algorithm in which the process having smallest execution time is chosen first for execution.
2. For example, consider two jobs A and B. A = 6 kilo bytes, B = 9 kilo bytes.
3. First job A will be assigned and then job $B$ will be executed,
(c) Round Robin:
1. Round Robin scheduling is especially designed for time sharing system
2. It is similar to FIFO but there is switching between processes.
3. For example, take three jobs A, B and C. First the job A is assigned to CPU then job B and job C and then again A, B and C and so on.

The Distributed Operating System is used to access shared data and files that reside in any machine around the world. The user can handle the data from different locations. The users can access as if it is available on their own computer.
The advantages of distributed Operating System are as follows:
(i) A user at one location can make use of all the resources available at another location over the network.
(ii) Many computer resources can be added easily in the network
(iii) Improves the interaction with the customers and clients.
(iv) Reduces the load on the host computer.