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Operating System - Overview OS Definition Memory Management  Processor Management  Device Management  File Management  Security  Error Detecting Aids  Job Accounting Operating System - Types  Batch Operating System Time-sharing Operating System Distributed Operating System Network Operating System Real-time Operating System Hard real-time Operating System Soft real-time Operating System Operating System - Services Program Execution  I/O Operations  File System Management  Communication  Error-handling  Resource Management  Protection  Operating System - Properties  Batch-processing Multi-tasking Multi-programming Interactivity  Real-time system Distributed Environment  Spooling  Operating System - Process Process Program Process Control Block (PCB) Operating System - Process Scheduling Definition Process Scheduling Queues Job Queue Ready Queue Device Queue Two-State Process Model  Running...

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...

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...

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...

Definition:   Process scheduling is the activity of the process manager that handles the removal of the running process from the CPU and the selection of another process on the basis of a particular strategy. Process Scheduling Queues (Job Queue, Ready Queue, Device Queue): Job queue - This queue keeps all the processes in the system. Ready queue - This queue keeps a set of all processes residing in the main memory, ready and waiting to execute. A new process is always put in this queue. Device queues - The processes which are blocked due to the unavailability of an I/O device constitute this queue. Two-State Process Model (Running, Not Running): Running: When a new process is created, it enters into the system as in the running state. Not Running: Processes that are not running are kept in a queue, waiting for their turn to execute. Scheduler (Long-Term Scheduler, Short-Term Scheduler, Medium-Term Scheduler): Schedulers are special system software that handle...

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...

Batch Processing:  Batch processing is a technique in which an Operating System collects the programs and data together in a batch before processing starts. Multitasking:  Multitasking is when multiple jobs are executed by the CPU simultaneously by switching between them. Multiprogramming:  Sharing the processor, when two or more programs reside in memory at the same time, is referred to as multiprogramming. Interactivity:  Interactivity refers to the ability of users to interact with a computer system. Real-Time System:  Real-time systems are usually dedicated, embedded systems. The Operating system must guarantee a response to events within fixed periods of time to ensure correct performance. Distributed Environment:  A distributed environment refers to multiple independent CPUs or processors in a computer system. The OS distributes computation logic among several physical processors. The processors do not share a memory or a clock. Instead, each proces...