Posted by Anisha Jaiswar at May 1, 2021
The operating system controls and coordinates the use of hardware among various application programs for various users . Various functions of operating system are
Basic Terms Associated With Operating System
Kernel is defined as a program running at all times on the computer. It is the part of operating system that loads first. In simple word kernel provides the communication between system software and hardware.
For a computer to start running for instances when it is powered up or rebooted, it needs to have an initial program to run. This initial program to run. This initial program is known as bootstrap program.
Bootstrap program is stored in ROM or EEPROM which is known as firmware.
System call provides an interface to the service made available by operating system.
Types of Operating System
Single processor system
there is one main CPU capable of executing a general purpose instruction set, including instructions from user processes.
(Parallel system or tightly coupled system)
The kind of system have to are more processor in close communication, sharing the computer bus and sametime the clock, memory and peripheral devices.
In cluster system, computer share storage and are closely linked via LAN.
Operating system structure
In multiprogramming system, the operating system keeps several jobs in main memory simultaneously. This set of jobs can be a subset of jobs kept in jobs pool. Job pool contains all jobs that enter in the operating system.
The operating system picks and beings to execute one of the jobs in memory, when the selected job goes to waiting state for some, the operating system simple switches to execute another job.
In multitasking system, the CPU execute multiple jobs by switching among them but the switches occur so frequently that the user can interact with each program while it is running.
A process is simply defined as program under execution. Thus, the difference between and program is that program is a passive entity whereas process is active entity.
When a process executes, it changes its state. The state of process is defined as part of the current activity of the process. Each process may be in one of the following states.
Interrupts cause the operating system to change a CPU from its current task and to run a kernel routine. When an interrupt occurs, the system needs to save current context of the process currently running on the CPU, so that it can restore that context when its processing is done, essentially suspending the process and then resuming it by switching the CPU to another process require performing a state, save of current process and a state restore of a different process. This task is known as a ‘context switch’. When context switch occurs, the kernel saves the context of the old process in its PCB and loads the saved context of the new process schedule to run.
In a single processor system, only one process can run at a time, any other must wait until the CPU is free and can be rescheduled. The goal of multiprogramming is to have some process running at all times, to maximize CPU utilization.