5.Operating System

5.Operating System - Process

Process: A process is basically a program in execution. The execution of a process must progress in a sequential fashion. To put it in simple terms, we write our computer programs in a text file and when we execute this program, it becomes a process that performs all the tasks mentioned in the program.

When a program is loaded into the memory and it becomes a process, it can be divided into four sections ─ stack, heap, text and data.

Program: A computer program is a collection of instructions that performs a specific task when executed by a computer. When we compare a program with a process, we can conclude that a process is a dynamic instance of a computer program.

Process Life Cycle (Start, Ready, Running, Waiting, Terminate/Exit):

Process Control Block (PCB): A Process Control Block is a data structure maintained by the Operating System for every process. The PCB is identified by an integer process ID (PID). A PCB keeps all the information needed to keep track of a process.

The architecture of a PCB is completely dependent on Operating System and may contain different information in different operating systems. The PCB is maintained for a process throughout its lifetime, and is deleted once the process terminates.

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1. Operating System - Overview

Definition: An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs. Memory Management: Memory management refers to the management of Primary Memory or Main Memory. It keeps track of primary memory, i.e., what part of it is in use by whom, what parts are not in use. It allocates and de-allocates the memory when a process requests it to do so. Processor Management : Processor Management k eeps track of the processor and the status of a process. The program responsible for this task is known as a traffic controller . It is responsible for a llocating and de-allocating the processor (CPU) to a process. Device Management : An Operating System manages device communication via their respective drivers. Device Management keeps track of all devices. The program responsible for this task is known as the I/O Controller. It d ecides which process gets the d...

8. Operating System - Virtual Memory and Input/Output

Definition: A computer can address more memory than the amount physically installed on the system. This extra memory is actually called virtual memory and it is a section of a hard disk that's set up to emulate the computer's RAM. The main visible advantage of this scheme is that programs can be larger than physical memory. Virtual memory serves two purposes. First, it allows us to extend the use of physical memory by using disk. Second, it allows us to have memory protection, because each virtual address is translated to a physical address. Demand Paging: A demand paging system is quite similar to a paging system with swapping where processes reside in secondary memory and pages are loaded only on demand, not in advance. Page Replacement Algorithm: Page replacement algorithms are the techniques using which an Operating System decides which memory pages to swap out, write to disk when a page of memory needs to be allocated Reference String: The string of memory references i...

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