Multi-processing is a one of the features of Operating System. It has two or more processors for a single running process (job). Processing takes place in parallel is known as parallel processing.

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

Ubuntu, Mint, Fedora, RedHat, Debian, Google's Android. Chrome OS, Chromium OS.

The GUI is a window based system with a pointing device to direct I/O, choose from menus, make selections and a keyboard to enter text. Its vibrant colours attract the user very easily.

Multi-user Operating Systems:
1. It is used in computers and laptops that allow same data and applications to be accessed by multiple users at the same time.
2. The users can also communicate with each other. Windows, Linux and UNIX are examples for multi-user Operating System.

(i) To ensure that a computer can be used to extract what the user wants it do.
(ii) Easy interaction between the users and computers

(i) Easy interaction between the human and computer.
(ii) Starting computer operation automatically when power in turned on (Booting).
(iii) Controlling input & output devices.
(iv) Managing the utilization of main memory.
(v) Providing security to user program.

A mobile operating system controls a mobile device and its design supports wireless communication and different types of mobile applications. It operates 012 smart phones Tablets and Digital Mobile devices.
(i) Google Android
(ii) Apple iOS
(iii) Blackberry
(iv) Symbian

(i) File management is an important function of OS which handles the data storage techniques. The operating System manages the files, folders and directory systems on a computer.
(ii) Any type of data in a computer is stored in the form of files and directories/folders through File Allocation Table (FAT).
(iii) The FAT stores general information about files like filename, type (text or binary), size, starting address and access mode (sequential/indexed / indexed-sequential/direct/relative).
(iv) The file manager of the operating system helps to create, edit, copy, allocate memory to the files and also. updates the FAT.
(v) The OS also takes care of the files that are opened with proper access rights to read or edit them. There are few other file management techniques available like Next Generation File System (NTFS) and ext2(Linux).

Memory Management:
(i) Memory Management is the process of controlling and coordinating computer's main memory and assigning memory block (space) to various running programs to optimize overall computer performance.
(ii) The Memory management involves the allocation of specific memory blocks to individual programs based on user demands. At the application level, memory management ensures the availability of adequate memory for each running program at all times.
(iii) The objective of Memory Management process is to improve both the utilization of the CPU and the speed of the computer's response to its users via main memory. For these reasons, the computers must keep several programs in main memory that associates with many different Memory Management schemes.
(iv) The Operating System is responsible for the following activities in connection with memory management.
(v) Keeping track of which portion of memory are currently being used and who is using them.
(vi) Determining which processes (or parts of processes) and data to move in and out of memory.
(vii) Allocation and de-allocation of memory blocks as needed by the program in main memory. (Garbage Collection).

The following algorithms are mainly used to allocate the job (process) to the processor.
(i) FIFO
(ii) SJF
(iii) Round Robin
(iv) Based on Priority
(i) FIFO (First In First Out) Scheduling :This algorithm is based on queuing technique Assume that a student is standing in a queue (Row) to get grade sheet from his/her teacher. The other student who stands first in the queue gets his/her grade sheet first and leaves from the queue (Row). Followed by the next student in the queue gets it corrected and so on. This is the basic logic of the FIFO algorithm.
(ii) SJF (Shortest Job First) Scheduling : This algorithm works based on the size of the job being executed by the CPU. Consider two jobs A and B.
1) A = 6 kilo bytes
2) B = 9 kilo bytes
First the job "A" will be assigned and then job "B" gets its turn.
(iii) Round Robin Scheduling : The Round Robin (RR) scheduling algorithm is designed especially for time sharing systems. Jobs (processes) are assigned and processor time in a circular method. For example take three jobs A, B, 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.
(iv) Based On Priority :The given job (process) is assigned based on a Priority. The job which has higher priority is more important than other jobs. Take two jobs A and B. Let the priority of A be 5 and priority B be 7. Job B is assigned to the processor before job A.