Operating System An Operating System is a large

Transcript:Operating System An Operating System is a large:
Operating System An Operating System is a large collection of software which acts as an interface between the user of a computer and the computer hardware. It manages the resources of a computer system, such as memory, processor, file system and Input/Output devices. It also keeps track of the status of each resource and decides who will have control over computer resources for how long and when. What is Operating System? The evolution of O/S involves several phases such as: Serial Processing – Here jobs are allotted to the processor one by one and after the completion of one job, the second one gets the processor time. Batch processing – Jobs are stored in the memory unit as job pool and the O/S can choose the next job to run. This is also called spooling, where the I/O operations can overlap with the processor time. Evolution of Operating System 3. Multiprogramming – In this case, many programs can run simultaneously using the time-sharing mechanism of the O/S. The CPU utilization increases in this case. Evolution of Operating System Functions of Operating System Simplifies the execution of user programs and make solving of user problems easier. Use computer hardware efficiently. It allows sharing of hardware and software resources. Provide isolation, security and protection among user programs. Improve overall system reliability through error confinement, fault tolerance, reconfiguration etc. Functions of Operating System The main functions of an O/S can broadly categorized as: Process Management Memory Management File Management Input / Output Management Security and Protection The concept of a Process A process is an executing program including the current values of the program counter, registers and variables. A program is a group of instructions whereas the process is the activity. For an O/S, process management functions include: Process creation Termination of a process The concept of a Process Controlling the process Process scheduling Dispatching Interrupt handling / Exception handling Switching between processes Process synchronization Inter-process communication support Management of Process Control Block (PCB) Process States A process has five states and at any given time, it remains in any one of those five states. New State: The process is being created Ready State: The process is waiting to be assigned to a processor Running State: Instructions are being executed Waiting / Suspended / Blocked: The process is waiting for some event to occur Halted : The process has finished execution. Transitions New