Difference Between Context Switching and Swapping

The article discusses the concepts of context switching and swapping in OS and covers the difference between context switching and swapping.

Swapping and Context Switching in OS are two related terms but have totally different contexts. Context Switching involves switching the process from running to the ready state, while Swapping refers to data exchange between the main and secondary memory. To learn more about these two terms, read the blog.

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Difference Between Context Switching and Swapping

What is Context Switching in OS?

Context Switching in OS is a process in which the CPU switches from one process to another, stores the current process’s context (state), and loads it into the new process (resume) whenever required. In simple terms, Context Switching is the process of storing the state of a process so that it can be restored and resumed later.

This process occurs when the CPU switches between two processes. The saved state of the current process copies all live registers to PCB (Process Control Block). Context Switching allows sharing of a single CPU by several processes.

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Context switches are computationally intensive and require some time for tasks like saving and loading registers and memory maps, updating various tables and lists, etc. Operating systems are designed to optimize the use of context switches. 

There are three potential triggers for context switching in OS:

Multitasking

Usually, in the scheduling scheme, one process must be switched out of the CPU to allow another process to run. The current process’s state is saved, and the new process is loaded. On a pre-emptive multitasking system, a scheduler may switch out the still runnable processes.

Interrupt handling

Modern architectures are interrupt driven. When an interrupt happens, the hardware automatically switches a part of the context. This changes some contexts to minimize the time wastage in the interrupt handling process.

User and Kernel Mode Switching

A mode transition is not a context switch by itself, and a context switch does not happen mandatorily if a system transitions between user mode and kernel mode. However, a context switch may happen depending on the OS.

What is Swapping?

Swapping in OS temporarily moves programs between primary and secondary memory, usually disk (Swap). The Swap is the space in the hard disk exchanging the physical and virtual memory. With swapping, programs can move in/out of/into memory during their execution time. It is a memory management technique that can improve the performance of an operating system. 

While swapping, the OS finds the first vacant block of physical memory and allocates the new memory block while replacing the oldest block in physical memory. If a program tries to access a swapped-out page, the OS copies the page from the disk into physical memory and updates the page table entry.

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Swap-out removes a program from the main memory and stores it on the hard disk or auxiliary storage (secondary memory).

Swapping provides the following advantages:

• Allows you to influence process management to control the degree of multiprogramming (medium-term planning).
• Provides flexibility in memory management, allowing more efficient use of space.

Conclusion

Understanding these two mechanisms enables system administrators and developers to make informed decisions about resource allocation, memory management strategies, and overall system performance optimization. The right combination of context switching and swapping techniques can enhance system stability, responsiveness, and overall user experience in various computing environments.