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Main functions of an operating system are: 1. Process management: A process is a program in execution. It is the job which is currently being executed by the processor. During its execution a process would require certain system resources such as processor, time, main memory, files etc. OS supports multiple processes simultaneously. The process management module of the as takes care of the creation and termination of the processes, assigning resources to the processes, scheduling processor time to different processes and communication among processes. 2. Memory management: It takes care of the allocation and deallocation of the main memory to the various processes. It allocates main and secondary memory to the system/user program and data. To execute a program, its binary image must be loaded into the main memory. OS decides: which part of memory are being currently used and by whom, which process to be allocated memory, Allocation and deallocation of memory space. 3. I/0 management: This module of the as co-ordinates and assigns different I/O devices namely terminals, printers, disk drives, tape drives etc. It controls all I/O devices, keeps track of I/O request, issues command to these devices. 4. File management: Data is stored in a computer system as files. The file management module of the as would manage files held on various storage devices and transfer of files from one device to another. This module takes care of creation, organization, storage, naming, sharing, backup and protection of different files. 5.Scheduling: The as also establishes and enforces process priority. That is, it determines and maintains the order in which the jobs are to be executed by the computer system. This is so because the most important job must be executed first followed by less important jobs. 6.Security management: This module of the OS ensures data security and integrity. That is, it protects data and program from destruction and unauthorized access. It keeps different programs and data which are executing concurrently in the memory in such a manner that they do not interfere with each other. 7. Processor management: as assigns processor to the different task that must be performed by the computer system. If the computer has more than one processor idle, one of the process waiting to be executed is assigned to the idle processor.