Thursday, December 13, 2007

Assignment #3

#4a.What is the cause of thrashing?
@Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault.

b. How does the system detect thrashing?
The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming.

c.Once it detects thrashing, what can the system do to eliminate this problem?
It can be eliminated by reducing the level of multiprogramming.

a.Multiprogrammng. Why is it to use?-The concept of multiprogramming is that the operating system keeps several jobs in memory simultaneously. The operating system selects a job from the job pool and starts executing a job, when that job needs to wait for any i/o operations the CPU is switched to another job. So the main idea here is that the CPU is never idle.

b.Internal Fragmentation.How does it occur?-
Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used

c.External Fragmentation. How does it occur?
External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.

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