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Pertemuan 19Disk

Matakuliah : T0316/sistem Operasi

Tahun : 2005

Versi/Revisi : 5

OFFCLASS03

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Learning Outcomes

Pada akhir pertemuan ini, diharapkan mahasiswa

akan mampu :• menjelaskan perangkat-perangkat disk dan cara

kerjanya (C2)

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Outline Materi

• Disk Hardware• RAID• CDROM• DVD• Interleaving• Disk Arm Scheduling

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Disks

Disk parameters for the original IBM PC floppy disk and a Western Digital WD 18300 hard disk

Disk Hardware (1)

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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)

• Raid levels 0 through 2 • Backup and parity drives are shaded

Split on write

Primary & backup

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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)

• Time required to read or write a disk block determined by 3 factors

1. Seek time

2. Rotational delay

3. Actual transfer time

• Seek time dominates

• Error checking is done by controllers

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• 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.

Disk Arm Scheduling Algorithms (1)

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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