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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7.Operating System - Memory Management

Process Address Space: The process address space is the set of logical addresses that a process references in its code. Static vs Dynamic Loading: The choice between Static or Dynamic Loading is to be made at the time of the computer program being developed. If you have to load your program statically, then at the time of compilation, the complete programs will be compiled and linked without leaving any external program or module dependency. If you are writing a dynamically loaded program, then your compiler will compile the program and for all the modules which you want to include dynamically, only references will be provided and the rest of the work will be done at the time of execution. At the time of loading, with static loading, the absolute program (and data) is loaded into memory in order for execution to start. If you are using dynamic loading, dynamic routines of the library are stored on a disk in re-locatable form and are loaded into memory only when they a...

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...

9. Operating System - Extra

Interrupt: In system programming, an interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. Trap: In computing and operating systems, a trap, also known as an exception or a fault, is typically a type of synchronous interrupt caused by an exceptional condition (e.g., breakpoint, division by zero, invalid memory access). Signal: A signal is a software-generated interrupt that is sent to a process by the OS because when the user press ctrl-c or another process tells something to this process. There is fix set of signals that can be sent to a process. Signals are identified by integers. A signal number has symbolic names. System call: The interface between a process and an operating system is provided by system calls. System calls are usually made when a process in user mode requires access to a resource. Then it request...

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