Swapping in Operating System

Last Updated on April 19, 2023 by Prepbytes

Operating Systems (OS) manage the allocation and usage of computer resources, including memory. One of the techniques used by OS to manage memory is swapping. In this article, we will explore the concept of swapping in operating system, including what it is, how swapping in operating system works, and the advantages and disadvantages of swapping in operating system. So, without any further delay, lets us move on to our next section.

What is Swapping in Operating System?

Swapping in operating system is an essential memory management technique that enables proper memory utilization and availability of memory for the execution of ready processes. Let’s understand this concept in detail with the given scenario:

Suppose there are several processes, P1, P2, P3, and P4, that are ready to be executed. However, P1 and P2 are memory-consuming processes, and when they start executing, the memory may not be available for the execution of P3 and P4, as the available memory is limited.

In this situation, the operating system uses swapping to temporarily transfer the idle or blocked process from the main memory to the secondary memory. This process ensures the proper utilization of memory and availability of memory for other processes that are ready to be executed.

When the memory-consuming process, like P1 or P2, terminates its execution, the memory dedicated to its execution becomes free, and the swapped-out processes are brought back into the main memory, and their execution starts again.

The area of the secondary memory where swapped-out processes are stored is called swap space. The swapping technique forms a temporary queue of swapped processes in the secondary memory.

In the case of high-priority processes, the process with low priority is swapped out of the main memory and stored in swap space, and the process with high priority is swapped into the main memory to be executed first.

Swapping in operating systems helps in accessing data present in the secondary memory and transferring it to the main memory for use by application programs. It can affect system performance, but it helps in running more than one process by managing the memory. Therefore, swapping in operating systems is also known as the memory compaction technique.

Swap In and Swap Out in Operating System

In the process of swapping, there are two important concepts known as Swap In and Swap Out. These two terms are used to describe the transfer of processes from the main memory to the secondary memory (swap space) and vice versa.

• Swap Out:
  Swap Out method is used to transfer processes from the main memory to the secondary memory (swap space) when the system is running low on memory. When a process is idle or blocked, it is swapped out of the main memory and saved to the swap space to free up space in the main memory. This process allows other processes to use the memory that was previously occupied by the swapped-out process.

  The swapped-out process is no longer available in the main memory, and the CPU does not execute any instructions for that process. Swap Out is commonly used when there are more processes running simultaneously than the available physical memory.

• Swap In:
  Swap In method is used to transfer processes from the secondary memory (swap space) back to the main memory when the CPU needs to execute the process again. When a process that was swapped out becomes active again, it is swapped back into the main memory from the swap space.

  The swapped-in process resumes its execution from where it left off, and the CPU can execute its instructions again. This process helps to improve the system’s performance by ensuring that the most critical processes are always in the main memory, and can be executed by the CPU when required.

Example of Swapping in Operating System

Let’s understand the concept of swapping in operating system with the help of an example.

Suppose there are four processes, P1, P2, P3, and P4, running in the system, and their memory requirements are as follows:

• P1 requires 1 GB of memory
• P2 requires 1 GB of memory
• P3 requires 500 MB of memory
• P4 requires 500 MB of memory

Suppose the total physical memory available in the system is only 2 GB. In this case, it is not possible to allocate memory for all the processes simultaneously, as the total memory requirement is 3 GB, which is more than the available memory.

In such a situation, the operating system uses the swapping technique to manage the memory requirements of the processes. Let’s see how the swapping process works:

Initially, processes P1 and P2 are loaded into the main memory, and processes P3 and P4 are swapped out to the secondary memory (swap space).

When the CPU needs to execute P3, it swaps in P3 from the swap space to the main memory and swaps out P1 to the swap space. Now, the main memory contains P2 and P3, and P1 is in the swap space along with P4.

Similarly, when the CPU needs to execute P4, it swaps in P4 from the swap space to the main memory and swaps out P2 to the swap space. Now, the main memory contains P3 and P4, and P1 and P2 are in the swap space.

When the CPU needs to execute P1 again, it swaps in P1 from the swap space to the main memory and swaps out P3 to the swap space. Now, the main memory contains P1 and P4, and P2 and P3 are in the swap space.

Finally, when the CPU needs to execute P2 again, it swaps in P2 from the swap space to the main memory and swaps out P4 to the swap space. Now, the main memory contains P1 and P2, and P3 and P4 are in the swap space.

Swapping in operating system manages the memory requirements of the processes efficiently and ensures that the critical processes are always in the main memory and can be executed by the CPU when required.

Advantages of Swapping in Operating System

Here are some advantages of swapping in operating system:

1. Efficient Memory Utilization: Swapping in the operating system allows for efficient utilization of memory resources. It helps to accommodate multiple processes that require more memory than the available memory space. When a process is not required, it is swapped out of the main memory to the secondary memory and replaced with another process.
2. Better System Performance: Swapping in operating system helps to improve the overall system performance. By freeing up memory space in the main memory, it allows more processes to be executed simultaneously, thereby increasing the overall throughput of the system.
3. Reduced Process Blocking: Swapping in operating system reduces the chances of process blocking due to memory unavailability. When a process is swapped out of the main memory, it is temporarily suspended until it is swapped back in. This helps to prevent processes from getting blocked due to memory unavailability.
4. Flexibility: Swapping in operating system provides flexibility to allocate memory resources as per the demand of the processes. It allows the operating system to accommodate processes with varying memory requirements.

Disadvantages of Swapping in Operating System

Here are some disadvantages of Swapping in operating system:

1. Performance Overhead: The swapping process involves reading and writing data to and from the secondary memory, which can be slow as compared to accessing data from the main memory.
2. Storage Overhead: Swapping in operating system requires dedicated space on the secondary memory to store the swapped-out processes. This can cause storage overhead, especially if the size of the swapped-out processes is large.
3. Data Integrity Issues: Swapping in operating system can lead to data integrity issues if the swapped-out process contains critical data that is not saved before the swapping process. In such a case, the data may be lost, leading to system crashes or data corruption.
4. Increased Disk Activity: Swapping increases disk activity, as the operating system needs to read and write data to and from the secondary memory. This can cause wear and tear on the disk and reduce its lifespan.

Conclusion
In conclusion, swapping in operating system is a memory management technique that allows for the efficient utilization of memory resources and improved system performance. However, it also has certain disadvantages that need to be balanced for optimum system performance and stability.

FAQs

Here are some frequently asked questions related to swapping in operating system.

Q1: What is Swap space in the operating system?
Answer: Swap space is the area of the secondary memory where swapped-out processes are stored.

Q2: How does Swapping affect system performance?
Answer: Swapping can affect system performance by causing performance overhead and increased disk activity.

Q3: How does Swapping in operating system help in running multiple processes?
Answer: Swapping in operating system helps in running multiple processes by managing memory efficiently and freeing up memory space for other processes.

Q4: How does the operating system decide which process to swap out?
Answer: The operating system decides which process to swap out based on factors like process priority, memory usage, and process state.

Q5: What is the difference between Paging and Swapping in operating system?
Answer: Swapping in operating system involves moving entire processes between main memory and secondary memory, while paging involves moving memory pages between main memory and secondary memory.

Q6: Can Swapping in operating systems cause data loss?
Answer: Swapping in operating systems can cause data loss if the swapped-out process contains critical data that is not saved before the swapping process.

Q7: Can Swapping in operating systems leads to system crashes?
Answer: Swapping in operating systems can lead to system crashes if the swapped-out process contains critical data that is not saved before the swapping process.