Circular SCAN (C-SCAN) scheduling is a variant of SCAN designed to
provide a more uniform wait time. Like SCAN, C-SCAN moves the head from
one end of the disk to the other, servicing requests along the way. When
the head reaches the other end, however, it immediately returns to the
beginning of the disk without servicing any requests on the return trip
(Figure 10.7). The C-SCAN scheduling algorithm essentially treats the
cylinders as a circular list that wraps around from the final cylinder to
the first one.Read more>>
C program for SCAN disk scheduling algorithm
In the SCAN algorithm, the disk arm starts at one end of the disk and
moves toward the other end,servicing requests as it reaches each
cylinder,until it gets to the other end of the disk. At the other end,
the direction of head movement is reversed, and servicing continues. The
head continuously scans back and forth across the disk. The SCAN
algorithm is sometimes called the elevator algorithm, since the disk arm
behaves just like an elevator in a building, first servicing all the
requests going up and then reversing to service requests the other way. Read more>>
C program for FCFS disk scheduling algorithm
The simplest form of disk scheduling is, of course, the first-come,
first-served (FCFS) algorithm. This algorithm is intrinsically fair, but
it generally does not provide the fastest service. Consider, for
example, a disk queue with requests for I/O to blocks on cylinders 98,
183, 37, 122, 14, 124, 65, 67. If the disk head is initially at
cylinder 53, it will first move from 53 to 98, then to 183, 37, 122, 14,
124, 65, and finally to 67, for a total head movement of 640 cylinders.
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C program for worst fit memory management algorithm
Allocate the largest hole. Again, we must search the entire list,
unless it is sorted by size. This strategy produces the largest left
over hole, which may be more useful than the smaller leftover hole from a
best-fit approach.Read more>>
C program for best fit memory management algorithm
Allocate the smallest hole that is big enough. We must search the
entire list, unless the list is ordered by size. This strategy produces
the smallest left over hole.Read more>>
C program for first fit memory management algorithm
Allocate the first hole that is big enough.Searching can start either at
the beginning of the set of holes or at the location where the previous
first-fit search ended.We can stop searching as soon as we find a free hole
that is large enough.Read more>>
C program for LFU page replacement algorithm
The least frequently used(LFU) page-replacement algorithm requires that
the page with the smallest count be replaced. The reason for this
selection is that an actively used page should have a large reference
count. A problem arises, however, when a page is used heavily during the
initial phase of a process but then is never used again. Since it was
used heavily, it has a large count and remains in memory even though it
is no longer needed. One solution is to shift the counts right by1bit at
regular intervals,forming an exponentially decaying average usage
count.Read more>>
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