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OPERATING SYSTEM COMPONENTS
There are eight major operating system components. They are:
v Process management
v Main-memory management
v File management
v I/O-system management
v Secondary-storage management
v Protection system
v Command-interpreter system
(i) Process Management
ü A process can be thought of as a program in execution. A batch job is a process. A time shared user program is a process.
ü A process needs certain resources-including CPU time, memory, files, and I/O devices-to accomplish its task.
ü A program by itself is not a process; a program is a passive entity, such as the contents of a file stored on disk, whereas a process is an active entity, with a program counter specifying the next instruction to execute.
ü A process is the unit of work in a system.
ü The operating system is responsible for the following activities in connection with process management:
ü Creating and deleting both user and system processes
ü Suspending and resuming processes
ü Providing mechanisms for process synchronization
ü Providing mechanisms for process communication
ü Providing mechanisms for deadlock handling
(ii) Main – Memory Management
ü Main memory is a large array of words or bytes, ranging in size from hundreds of thousands to billions. Each word or byte has its own address.
ü Main memory is a repository of quickly accessible data shared by the CPU and I/O devices.
ü To improve both the utilization of the CPU and the speed of the computer's response to its users, we must keep several programs in memory.
ü The operating system is responsible for the following activities in connection with memory management:
ü Keeping track of which parts of memory are currently being used and by whom.
(iii) File Management
ü File management is one of the most visible components of an operating system.
ü The operating system is responsible for the following activities in connection with file management:
ü Creating and deleting files
ü Creating and deleting directories
ü Supporting primitives for manipulating files and directories
ü Mapping files onto secondary storage
ü Backing up files on stable (nonvolatile) storage media
(iv)I/O System management
ü One of the purposes of an operating system is to hide the peculiarities of
specific hardware devices from the user. This is done using the I/O subsystem.
ü The I/O subsystem consists of a memory-management component that includes buffering, caching, and spooling.
ü A general device-driver interface
ü Drivers for specific hardware devices
(v) Secondary storage management
ü Because main memory is too small to accommodate all data and programs, and
because the data that it holds are lost when power is lost, the computer system must provide secondary storage tobackupmainmemory.
ü The operating system is responsible for the following activities in connection with disk management:
§ Free-space management
§ Storage allocation
§ Disk Scheduling
ü A distributed system is a collection of processors that do not share memory, peripheral devices, or a clock.
ü Instead, each processor has its own local memory and clock, and the processors communicate with one another through various communication lines, such as high-speed buses or networks.
ü The processors in the system are connected through a communication network, which can be configured in a number of different ways.
(vii) Protection System
ü Various processes must be protected from one another's activities. For that purpose, mechanisms ensure that the files, memory segments, CPU, and other resources can be operated on by only those processes that have gained proper authorization from the operating system.
ü Protection is any mechanism for controlling the access of programs, processes, or users to the resources defined by a computer system.
ü Protection can improve reliability by detecting latent errors at the interfaces between component subsystems.
(viii) Command-Interpreter System
ü One of the most important systems programs for an operating system is the command interpreter.
ü It is the interface between the user and the operating system.
ü Some operating systems include the command interpreter in the kernel. Other operating systems, such as MS-DOS and UNIX, treat the command interpreter as a special program that is running when a job is initiated, or when a user first logs on (on time-sharing systems).
ü Many commands are given to the operating system by control statements.
ü When a new job is started in a batch system, or when a user logs on to a time-shared system, a program that reads and interprets control statements is executed automatically.
ü This program is sometimes called the control-card interpreter or the command-line interpreter, and is often known as the shell.
1. Main Memory
· referred to as real memory or primary memory
2. I/O modules
· secondary memory devices
· communications equipment
3. System bus
communication among processors, memory, andI/O modules.
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