20.4. Allocation of Frames

Now, allocation of frames; now still now we are saying that a page does not a page frames have no connection with the processes. Now, this is entirely not true. So, each process requires a minimum number of frames.

In this chunk, we are introduced to the idea that pages and frames are related to individual processes. Each process, essentially a separate program being executed by the computer, requires a certain number of frames in memory to operate effectively. This is important because it changes the earlier assumption that frame allocation was arbitrary and not connected to the processes themselves. Every process has specific memory needs based on the size and nature of the tasks it is performing.

Imagine a hotel that has a limited number of rooms (frames) available. Each guest (process) requires a certain number of rooms based on their needs. Some guests might come alone and need just one room, while others might arrive with family and require multiple rooms. Just like the hotel has to allocate rooms based on the guests' needs, the operating system must allocate memory frames based on the requirements of each process.

For example, the first strategy is the fixed allocation scheme. In the fixed allocation scheme let us say I have 100 frames in physical memory after these 100 frames are available after allocating frames to the OS and I have 5 processes. So, the degree of multi programming is 5, I give each process 20 frames.

The fixed allocation scheme is a method where a specific number of frames are allocated to each process without considering their individual needs. In this example, with 100 frames of memory and 5 processes, each process is assigned 20 frames. This strategy is straightforward but may not be efficient, as it does not account for differences in the memory requirements of individual processes. For instance, if one process requires more memory than allocated, it may not function correctly, leading to inefficiencies.

Think of a family picnic where 5 families each receive exactly 20 sandwiches, regardless of how many members each family has. If one family has 10 members and another has only 2, the first family will quickly run out of food, while the second family might have leftovers. This method of allocation can lead to waste or shortage, just like fixed allocation can lead to inefficient use of memory in computing.

Otherwise we can do a proportional allocation, I allocate fairly based on the process size.

In contrast to fixed allocation, the proportional allocation scheme allocates memory frames based on the size of each process. This method takes into account how much memory each process realistically needs. For instance, if one process requires more memory for its operations, it will receive more frames compared to a smaller process. This can lead to more efficient utilization of memory, as resources are allocated according to actual need rather than an arbitrary distribution.

Imagine a resource distribution scenario where food is allocated to households based on the number of family members. If a household has 4 members, they receive more food compared to a household with only 2 members. This ensures that each family gets a fair share relative to their size, just as proportional allocation ensures that processes receive memory based on their actual requirements.

Now, priority based allocation is proportional allocation using priorities.

This method introduces an additional layer of complexity by assigning priorities to processes. Instead of only looking at their sizes, it prioritizes processes based on their importance or urgency. When allocating frames, the system first tries to allocate frames from high-priority processes, and if no frames are available, it looks for a frame to replace from lower-priority processes. This strategy allows more critical processes to have sufficient memory resources to function well.

Think of a hospital emergency room where patients are treated based on the severity of their condition. A patient with a critical injury (high priority) will receive immediate attention and resources, while a patient with a minor issue (low priority) will have to wait. Similarly, priority-based allocation ensures that more important processes in a computing environment get the memory they need first.

Now, after this we come to the concept of thrashing.

The section concludes by transitioning into the concept of thrashing, which occurs when there are insufficient resources, causing excessive paging and replacement of frames. This situation can arise from improper allocation of frames, where processes do not have enough memory to work with, leading to significant performance degradation. Understanding frame allocation helps prevent such scenarios.

Imagine a busy restaurant where each table is constantly being served customers, but there aren’t enough staff members. If the waiters have to keep running back and forth because they can't handle the number of customers, service slows down significantly. This is similar to thrashing in computing, which slows down the system when it tries to handle too many processes without enough frames.

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