ITEC 502 컴퓨터 시스템 및 실습 Chapter 9-1: Disk Scheduling Mi-Jung Choi DPNM Lab. Dept. of CSE, POSTECH

ITEC502 컴퓨터 시스템 및 실습 2 Contents  Disk Hardware  Disk Formatting  Disk Arm Scheduling Algorithms

ITEC502 컴퓨터 시스템 및 실습 3 Moving-head Disk Machanism

ITEC502 컴퓨터 시스템 및 실습 4 Disks Disk Hardware (1) Disk parameters for the original IBM PC floppy disk and a Western Digital WD hard disk

ITEC502 컴퓨터 시스템 및 실습 5 Disk Hardware (2)  Physical geometry of a disk with two zones  A possible virtual geometry for this disk

ITEC502 컴퓨터 시스템 및 실습 6 Disk Hardware (3)  Raid levels 0 through 2  Backup and parity drives are shaded

ITEC502 컴퓨터 시스템 및 실습 7 Disk Hardware (4)  Raid levels 3 through 5  Backup and parity drives are shaded

ITEC502 컴퓨터 시스템 및 실습 8 Disk Hardware (5) Recording structure of a CD or CD-ROM

ITEC502 컴퓨터 시스템 및 실습 9 Disk Hardware (6) Logical data layout on a CD-ROM

ITEC502 컴퓨터 시스템 및 실습 10 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

ITEC502 컴퓨터 시스템 및 실습 11 Disk Hardware (8) A double sided, dual layer DVD disk

ITEC502 컴퓨터 시스템 및 실습 12 Disk Formatting (1) A disk sector

ITEC502 컴퓨터 시스템 및 실습 13 Disk Formatting (2) An illustration of cylinder skew

ITEC502 컴퓨터 시스템 및 실습 14 Disk Formatting (3)  No interleaving  Single interleaving  Double interleaving

ITEC502 컴퓨터 시스템 및 실습 15 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

ITEC502 컴퓨터 시스템 및 실습 16 Disk Arm Scheduling Algorithms (2) Shortest Seek First (SSF) disk scheduling algorithm Initial position Pending requests

ITEC502 컴퓨터 시스템 및 실습 17 Disk Arm Scheduling Algorithms (3) The elevator algorithm for scheduling disk requests