An operating system has various components that perform different tasks for proper execution of programs. Following are main components of the operating system.
A process can be a program in execution that needs resources like CPU time, memory, files and I/O devices to accomplish its tasks. The operating system is responsible for……
⭐ Creating and terminating user and system processes
⭐ Suspending and resuming processes
⭐ Providing mechanisms for process synchronization
⭐ Providing mechanisms for process communication Providing mechanisms for deadlock handling
Main Memory Management
Main memory is a large array of words or bytes. These bytes are called memory locations and range in size from hundreds of thousands to billions. Every word or byte has its own address. Main memory is a repository of quickly accessible data shared by the CPU and I/O devices. It contains the code, data, stack, and other parts of a process. The central processor reads instructions of a process from main memory during the machine cycle. The OS is responsible for the following activities in connection with memory management.
⭐ Keeping track of free memory space
⭐ Keeping track of which parts of memory are currently being used and by whom
⭐ Deciding which processes are to be loaded into memory when memory space becomes available
⭐ Deciding how much memory is to be allocated to a process
⭐ Allocating and deallocating memory space as needed
⭐ Ensuring that a process is not overwritten on top of another
Secondary Storage Management
The programs to be executed, along with the data they access, must be in the main memory or primary storage during their execution. Since main memory is too small to accommodate all data and programs, and because the data it holds are lost when the power is lost, the computer system must provide secondary storage to backup main memory. Most programs are stored on a disk until loaded into the memory and then use disk as both the source and destination of their processing. Like all other resources in a computer system, proper management of disk storage is important.
The operating system is responsible for the following activities in connection with disk management-
⭐ Free-space management
⭐ Storage allocation and deallocation
⭐ Disk scheduling
⭐ The input and output subsystem consists of-
⭐ A memory management component that includes buffering, caching and spooling
⭐ A general device-driver interface
⭐ Drivers for specific hardware devices
Computers can store information on several types of physical media, e.g. magnetic tape, magnetic disk and an optical disk. The operating system maps files onto physical media and accesses these media through storage devices. Operating system is responsible for the following activities pertaining to file management
⭐ Creating and deleting files
⭐ Creating and deleting directories
⭐ Supporting primitives (operations) for manipulating files and directories
⭐ Mapping files onto the secondary storage
⭐ Backing up files on stable (non-volatile) storage media
If a computer system has multiple users and allows concurrent execution of multiple processes then the various processes must be protected from each other’s activities. Protection is any mechanism for controlling the access of programs, processes or users to the resources defined by a computer system.
A distributed system is a collection of processors that do not share memory, peripheral devices or a clock. Instead, each processor has it own local memory and clock, and the processors communicate with each other through various communication lines, such as high-speed buses or networks.
The processors in a communication system are connected through a communication network. The communication network design must consider message routing and connection strategies and the problems of contention and security.
A distributed system collects physically separate, possibly heterogeneous, systems into a single coherent system, providing the user with access to the various resources that the system maintains.
Command Line Interpreter
One of the most important system programs for an operating system is the command interpreter. Which is the interface between the user and operating system. Its purpose is to read user commands and try to execute them. Some operating systems include the command interpreter in the kernel. Other operating systems (for example UNIX, Linux, and DOS) treat it as a special program that runs when a job is initiated or when a user first logs on (on time-sharing systems). Examples of shells for UNIX and Linux are Bourne shell (sh), C shell (csh), Bourne Again shell (bash), TC shell (tcsh), and Korn shell (ksh). You can use any of these shells by running the corresponding command, listed in parentheses for each shell.