Thursday, December 13, 2007

Assignment 3

1.What is the cause of thrashing?

-There is currently one user and he is not doing anything. The drive is showing a lot of activity. There is adequate disk space, and the machine is not an http, nis, or nfs server. The machine reaches this state of "thrashing", for lack of knowledge as to what's going on, after several weeks uptime, with no apparent difference in load by the few users that work on it.

2.How does the operating system detect

-The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming.

3.Once it detects thrashing, what can the system do to eliminate this problem?

-It can be eliminated by reducing the level of multiprogramming.

1.Explain the following:

a.Multiprogramming. Why is it used?

-The interleaved execution of two or more programs by a computer, in which the central processing unit executes a few instructions from each program in succession.

b.Internal Fragmentation.How does it occur?

-Internal fragmentation occurs as a failure of the file system to store the file with enough precise enough a granularity such that all available free space is utilized. This occurs because reduced granularity allows for increased performance or simplicity when implementing the file system. Internal fragmentation on most computer systems is not usually considered a problem, because optimizing it invokes only small performances benefits, and involves modifying the file system, which can lead to a host of compatibility issues.

c.External Fragmentation. How does it occuInternal

-External fragmentation occurs to the free space on the hard drive, after data has been removed. Ideally, free space would be kept contiguously, so that data can be written to the medium contiguously and without fragmentation. However, if segments of data are removed at arbitrary places along the storage medium, then the free space is automatically fragmented. Ideally, a storage medium would be able to shuffle files into that free space and reallocate the free space back to a "heap" of it, however this is time consuming. This can be seen in defragmentation software, which utilize significant amounts of time to defragment heavily fragmented disks.

d.Compaction. Why is it needed?

- In a data center, compaction is the reduction or consolidation of hardware to make better use of physical floor space. Although the goal of compaction is to be cost-effective and maximize real estate, increased hardware compaction puts more demands on power consumption and cooling requirements, two major cost elements in maintaining a large data center.-In storage area management (SAM), compaction is the automatic removal of expired data from a storage area network (SAN) to condense the existing archive and make room for new data.

e. Relocation. How often should it be performed?

-Once the relocation of the iliac artery bifurcation is completed, timing of the endovascular procedure is crucial. In a thin patient with appropriate anatomy, the endovascular aneurysm repair could be performed immediately after iliac bifurcation relocation, in which case the abdominal incision is kept open, and saline-soaked sponges are applied to the wound. In more complicated cases or obese patients, procedures should be staged at 7 to 10 days to prevent bleeding during heparinization for the endoluminal procedure.

2.Describe the major disadvantages for each of the four memory allocation scheme.

--The major disadvantage for each of the four memory allocation schemes presented is only 1 job per partition and waste of storage.

3.Describe the major advantages for each of the memory allocation schemes presented.

-The major advantage is easy to manage and implement.

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