In operating system how frames are allocated and what is the algorithm of allocation of frames and also discussed about Thrashing for clear some ideas! . Thank u!.

1. Allocation of Frame & Thrashing
Presented by-
Arif Mollick
3rd Year(6th Sem.)
CSE Dept.
11100116051

2. What is Allocation of Frame?
Consider a single-user system with 128 KB of memory composed of pages 1 KB in size. This
system has 128 frames. The operating system may take 35 KB, leaving 93 frames for the
user process. Under pure demand paging, all 93 frames would initially be put on the free-
frame list. When a user process started execution, it would generate a sequence of page
faults. The first 93 page faults would all get free frames from the free-frame list.
When the free-frame list was exhausted, a page-replacement algorithm would be used to
select one of the 93 in-memory pages to be replaced with the 94th, and so on. When the
process terminated, the 93 frames would once again be placed on the free-frame list. There
are many variations on this simple strategy. When this space is not in use by the operating
system/ it can be used to support user paging. We can try to keep three free frames
reserved on the free-frame list at all times. Thus, when a page fault occurs, there is a free
frame available to page into. While the page swap is taking place, a replacement can be
selected, which is then written to the disk as the user process continues to execute. Other
variants are also possible. The user process is allocated any free frame

3. Algorithm for allocation of frames?
❖ The two algorithms commonly used to allocate frames to a process are:
➢ Equal Allocation of frame: Each process gets equal number of frames.
➢ Proportional Allocation of frame: Frames are allocated to each process
according to the process size.

4. Constraints of Allocation of frames
★ You cannot allocate more than the total number of available frames.
★ At least a minimum number of frames should be allocated to each process.
★ As less number of frames are allocated, there is an increase in the page
fault ratio, decreasing the performance of the execution of the process.
★ Number of allocation of frame is defined by instruction set architecture.

5. Thrashing
❖ Swapping out a piece of a process just before that piece
is needed.
❖ The processor spends most of its time swapping pieces
rather than executing user instructions
❖ This activity is called the thrashing

6. Thrashing
❖ If a does not have enough pages,the page fault rate is very
high. This leads to :
➢ Low CPU utilization.
➢ OS thinks that it needs to increase the degree of
multiprogramming.
➢ Another process added to the system.
➢ A process is busy swapping page in and out.
➢ The high paging activity is called Thrashing.

7. Thrashing

8. Disadvantages of Thrashing
❖ Increase the degree of multiprogramming.
❖ System throughput decreases.
❖ Page fault rate increases.
❖ Effective access time increases.

9. Reduce the effect of Thrashing
❖ Using local replacement algorithm.
❖ Provides as many frames as it needs.
❖ Increase the size of memory.
❖ Decrease the number of process running.

10. Thank You.