1. C-SCAN Scheduling
• C-SCAN Scheduling is a variant of SCAN
Scheduling
• It is designed to provide uniform wait time
• Like SCAN, C-SCAN moves the head from one end
of the disk to other end, servicing requests along the
way
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2. C-SCAN Scheduling
• When the head reaches the other end,
– it immediately returns to the beginning of the disk,
– without servicing any requests on the return trip
• Treats the cylinders as a circular list that wraps
around from the last cylinder to the first one
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3. C-SCAN Scheduling
• Consider for example an ordered disk queue with
requests involving
– Tracks 98, 183, 37, 122, 14, 124, 65, 67
– Head pointer 53
• The request queue (0-199)
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4. C-SCAN Scheduling
• If the disk head is initially at cylinder 53,
– it will first move from 53 to 65, (towards right)
– then to 67, 98, 122, 124, 183,199, 0, 14 and 37 as shown in
the next slides
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16. C-SCAN Scheduling
• Advantages
– Better than SCAN Scheduling in terms of waiting
time
– i.e., provides uniform waiting time
• Disadvantages
– It is not optimal
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