Mid Term Scheduler & Swapping
The Medium-term Scheduler, also known as the Swapper, plays a crucial role in memory management in an operating system.
What it does:
The medium-term scheduler is responsible for swapping out processes from main memory to secondary memory (disk) and vice versa. This is known as swapping.
It removes processes from the CPU for a duration and reduces the degree of multiprogramming. After some time, these processes can again be reintroduced into main memory.
The process execution will again be resumed from the point it left the CPU.
Why it does it:
Swapping may be necessary to improve the process mix or because a change in memory requirements has overcommitted available memory, requiring memory to be freed up.
It helps in maintaining a perfect balance between the I/O bound and the CPU bound.
It reduces the degree of multiprogramming.
For example, the medium-term scheduler may decide to swap out a process which has not been active for some time, or a process which has a low priority, or a process which is page faulting frequently, or a process which is taking up a large amount of memory in order to free up main memory for other processes⁵. The process is then swapped back in later when more memory is available, or when the process has been unblocked and is no longer waiting for a resource⁵.
Summary of Swapping
Swapping is a memory management technique used in operating systems. Here's what it does:
Swap Out: Swapping involves temporarily moving (swapping out) an idle or blocked process from the main memory to secondary memory (like a hard disk). This is done to ensure proper memory utilization and memory availability for those processes which are ready to be executed.
Swap In: The process that was swapped out can be brought back (swapped in) into the main memory from the secondary memory when it needs to be executed.
Why it's used:
Memory Utilization: Swapping helps in managing the limited main memory more efficiently. It ensures that memory is allocated to those processes which are currently in execution or are ready to execute.
Multiprogramming: Swapping allows more processes to be loaded into main memory than can fit at one time, thus enabling multiprogramming.
Blocked Process Management: If a process is blocked (waiting for I/O operation to complete, for example), instead of keeping it in main memory, the operating system can swap out the process to make room for other processes².
However, swapping has its disadvantages. It may lead to inefficiency if a resource or a variable is commonly used by multiple processes. Also, the process of swapping requires significant time (known as swap time) which can affect system performance. Despite these challenges, swapping is a fundamental aspect of memory management in operating systems.
In summary, the medium-term scheduler plays a vital role in managing memory utilization and ensuring efficient execution of processes by performing swapping operations¹²⁴⁵.
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