INTERVIEW QUESTIONS OPERATING SYSTEMS DETAILS

Question: What is Context Switch?

Answer: Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process. This task is known as a context switch. Context-switch time is pure overhead, because the system does no useful work while switching. Its speed varies from machine to machine, depending on the memory speed, the number of registers which must be copied, the existed of special instructions(such as a single instruction to load or store all registers).

Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process. This task is known as a context switch. Context-switch time is pure overhead, because the system does no useful work while switching. Its speed varies from machine to machine, depending on the memory speed, the number of registers which must be copied, the existed of special instructions(such as a single instruction to load or store all registers). Source: CoolInterview.com

This will be fairly basic. A single core CPU can only serve one program at a time. In the days before windows on PCs, you could only run one program. When you wanted to run another program you had exit the one program and start the other one. With a multi-tasking operating system such a windows NT and above, Linux, and MAC OX/10, there is a process called context switching that lets multiple program share the CPU. When the operating system decides to give the processor to a different program it will tell program A to pause and tell Program B to run. The process of switch the CPU between program A and program B is the context switch. Source: CoolInterview.com

Selecting a new process from a ready state is called context switching. Source: CoolInterview.com

Switching the cpu to another process require saving the state of old processor and loading the saved stack for new process. Its speed typical ranges from 1 to 1000 microseconds. Source: CoolInterview.com

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