3.Operating System

3.Operating System - Services

Program Execution: The OS is responsible for executing programs. It loads the program into memory and executes the program. Program execution also includes process sync, process communication, and deadlock handling.

I/O Operation: An I/O subsystem comprises I/O devices and their corresponding driver software. I/O operation means read or write operation with any file or any specific I/O device. OS provides the access to the required I/O device when required.

File System Manipulation: A file represents a collection of related information. A file system is normally organized into directories for easy navigation and usage. The operating system gives the permission to the program for operation on file. Permission varies from read-only, read-write, denied, and so on. Operating System provides an interface for the user to create/delete files. Operating System provides an interface for the user to create/delete directories. Operating System provides an interface to create the backup of file system.

Communication: In the case of distributed systems which are a collection of processors that do not share memory, peripheral devices, or a clock, the operating system manages communications between all the processes. Multiple processes communicate with one another through communication lines in the network. The OS handles routing and connection strategies, and the problems of contention and security. Both the processes can be on one computer or on different computers, but are connected through a computer network. Communication may be implemented by two methods, either by Shared Memory or by Message Passing.

Error Handling: Errors can occur anytime and anywhere. An error may occur in the CPU, in I/O devices, or in the memory hardware. The OS constantly checks for possible errors. The OS takes an appropriate action to ensure correct and consistent computing.

Resource Management: In the case of multi-user or multi-tasking environment, resources such as main memory, CPU cycles and files storage are to be allocated to each user or job. The OS manages all kinds of resources using schedulers. CPU scheduling algorithms are used for better utilization of CPU.

Protection: Considering a computer system having multiple users and concurrent execution of multiple processes, the various processes must be protected from each other's activities. The OS ensures that all access to system resources is controlled. The OS ensures that external I/O devices are protected from invalid access attempts. The OS provides authentication features for each user by means of passwords.

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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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