The various functions of operating system are as follows:
1. Process Management:
• A program does nothing unless their instructions are executed by a CPU.A process is a program in execution. A time shared user program such as a complier is a process. A word processing program being run by an individual user on a pc is a process.
• A system task such as sending output to a printer is also a process. A process needs certain resources including CPU time, memory files & I/O devices to accomplish its task.
• These resources are either given to the process when it is created or allocated to it while it is running. The OS is responsible for the following activities of process management.
• Creating & deleting both user & system processes.
• Suspending & resuming processes.
• Providing mechanism for process synchronization.
• Providing mechanism for process communication.
• Providing mechanism for deadlock handling.
2. Main Memory Management:
The main memory is central to the operation of a modern computer system. Main memory is a large array of words or bytes ranging in size from hundreds of thousand to billions. Main memory stores the quickly accessible data shared by the CPU & I/O device. The central processor reads instruction from main memory during instruction fetch cycle & it both reads &writes data from main memory during the data fetch cycle. The main memory is generally the only large storage device that the CPU is able to address & access directly. For example, for the CPU to process data from disk. Those data must first be transferred to main memory by CPU generated E/O calls. Instruction must be in memory for the CPU to execute them. The OS is responsible for the following activities in connection with memory management.
• Keeping track of which parts of memory are currently being used & by whom.
• Deciding which processes are to be loaded into memory when memory space becomes available.
• Allocating &deallocating memory space as needed.
3. File Management:
File management is one of the most important components of an OS computer can store information on several different types of physical media magnetic tape, magnetic disk & optical disk are the most common media. Each medium is controlled by a device such as disk drive or tape drive those has unique characteristics. These characteristics include access speed, capacity, data transfer rate & access method (sequential or random).For convenient use of computer system the OS provides a uniform logical view of information storage. The OS abstracts from the physical properties of its storage devices to define a logical storage unit the file. A file is collection of related information defined by its creator. The OS is responsible for the following activities of file management.
• Creating & deleting files.
• Creating & deleting directories.
• Supporting primitives for manipulating files & directories.
• Mapping files into secondary storage.
• Backing up files on non-volatile media.
4. I/O System Management:
One of the purposes of an OS is to hide the peculiarities of specific hardware devices from the user. For example, in UNIX the peculiarities of I/O devices are hidden from the bulk of the OS itself by the I/O subsystem. The I/O subsystem consists of:
• A memory management component that includes buffering, catching & spooling.
• A general device- driver interfaces drivers for specific hardware devices. Only the device driver knows the peculiarities of the specific device to which it is assigned.
5. Secondary Storage Management:
The main purpose of computer system is to execute programs. These programs with the data they access must be in main memory during execution. As the main memory is too small to accommodate all data & programs & because the data that it holds are lost when power is lost.
The computer system must provide secondary storage to back-up main memory. Most modern computer systems are disks as the storage medium to store data & program. The operating system is responsible for the following activities of disk management.
• Free space management.
• Storage allocation.
• Disk scheduling
Because secondary storage is used frequently it must be used efficiently.