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Matakuliah
Tahun
Versi/Revisi
: T0316/sistem Operasi
: 2005
:5
Pertemuan 19
Disk
OFFCLASS03
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• menjelaskan perangkat-perangkat disk dan cara
kerjanya (C2)
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Outline Materi
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Disk Hardware
RAID
CDROM
DVD
Interleaving
Disk Arm Scheduling
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Disks
Disk Hardware (1)
Disk parameters for the original IBM PC floppy disk and
a Western Digital WD 18300 hard disk
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Disk Hardware (2)
• Physical geometry of a disk with two zones
• A possible virtual geometry for this disk
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Disk Hardware (3)
Split on write
Primary &
backup
• Raid levels 0 through 2
• Backup and parity drives are shaded
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Disk Hardware (4)
• Raid levels 3 through 5
• Backup and parity drives are shaded
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Disk Hardware (5)
Recording structure of a CD or CD-ROM
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Disk Hardware (6)
Logical data layout on a CD-ROM
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Disk Hardware (7)
• Cross section of a CD-R disk and laser
– not to scale
• Silver CD-ROM has similar structure
– without dye layer
– with pitted aluminum layer instead of gold
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Disk Hardware (8)
A double sided, dual layer DVD disk
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Disk Formatting (1)
A disk sector
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Disk Formatting (2)
An illustration of cylinder skew
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Disk Formatting (3)
• No interleaving
• Single interleaving
• Double interleaving
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Disk Arm Scheduling Algorithms (1)
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Time required to read or write a disk
block determined by 3 factors
1. Seek time
2. Rotational delay
3. Actual transfer time
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Seek time dominates
Error checking is done by controllers
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Disk Arm Scheduling Algorithms (1)
• FCFS
• Eg.
– Disk with 40 cylinders
– Request comes from cylinder 11
– New requests come from cylinder
• 1, 36, 16, 34, 9, and 12
– Total of arm motions:
• 10, 35, 20, 18, 25 and 3.
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Disk Arm Scheduling Algorithms (2)
Shortest Seek First (SSF) disk scheduling algorithm
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Disk Arm Scheduling Algorithms (3)
The elevator algorithm for scheduling disk requests
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