Computers12 Ch6

Mongolia International University

Chapter 6Chapter 6

B.M.HB.M.H

Storage and Storage and MultimediaMultimedia

MIUComputers

IndexIndex

Secondary StorageSecondary Storage Magnetic Disk StorageMagnetic Disk Storage

DiskettesDiskettes Hard DisksHard Disks

Data Organization on a DiskData Organization on a Disk

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Computer SystemComputer System

HardwareHardware Input devicesInput devices Output devicesOutput devices Processor and MemoryProcessor and Memory Secondary StoragesSecondary Storages

SoftwareSoftware System SWSystem SW Applications SWApplications SW

PeoplePeople

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Computer systemComputer system

Input Processing Output

SecondaryStorage

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Secondary StorageSecondary Storage

Benefits Benefits SpaceSpace ReliabilityReliability ConvenienceConvenience Economy Economy

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Secondary StorageSecondary Storage

TypesTypes Magnetic disk storageMagnetic disk storage

Diskettes, Hard Disks Magnetic tape storageMagnetic tape storage Optical disk storageOptical disk storage

CD, DVD

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Magnetic Disk StorageMagnetic Disk Storage

Magnetic mediaMagnetic media a technology of representing data as a technology of representing data as

magnetized spots on the surface of a magnetized spots on the surface of a spinning diskspinning disk

A magnetized spot : 1 bit The absence of such a spot : 0 bit

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Magnetic Disk StorageMagnetic Disk Storage

Reading data from the diskReading data from the disk Converting the magnetized data to Converting the magnetized data to

electrical impulseselectrical impulses

Writing data to diskWriting data to disk Converting electrical impulses from the Converting electrical impulses from the

processor to magnetized spots on the diskprocessor to magnetized spots on the disk

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Magnetic Disk StorageMagnetic Disk Storage

TypesTypes DiskettesDiskettes Hard disksHard disks

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Diskettes Diskettes

Made of flexible MylarMade of flexible Mylar Coated with iron oxide, Coated with iron oxide,

a substance that can be magnetizeda substance that can be magnetized TypesTypes

The standard floppy disk : The standard floppy disk : 3 1/2-inch diskette 1.44 megabytes of data

Two new high-capacity drives : Two new high-capacity drives : 120 or 200 megabytes per disk

Iomega’s Zip drive :Iomega’s Zip drive : 250-megabyte disks Is not compatible with 31/2-inch diskettes

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Hard DiskHard Disk

A rigid platter coated with magnetic A rigid platter coated with magnetic oxideoxide

Sizes : variousSizes : various Capacity for PCCapacity for PC

Older ones : hundreds of megabytesOlder ones : hundreds of megabytes New ones : tens of gigabytes of storageNew ones : tens of gigabytes of storage

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Hard DiskHard Disk

Disk packDisk pack assembles several plattersassembles several platters ComponentsComponents

Platters Access arms Read/write heads

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Hard Disks in GroupsHard Disks in Groups

RAIDRAID((RRedundant edundant AArray of rray of IIndependent ndependent ddisks)isks) Uses a group of small hard disks that work Uses a group of small hard disks that work

together as a unittogether as a unit Used for storage system to be safeUsed for storage system to be safe TypesTypes

RAID level 1 Higher levels of RAID

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Data organization on a Data organization on a diskdisk

Several characteristicsSeveral characteristics TrackTrack SectorsSectors ClustersClusters Cylinder Cylinder

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Disk driveDisk drive

A device that allows data to be read A device that allows data to be read from a disk or written to a diskfrom a disk or written to a disk

The performanceThe performance One measure : One measure : average access timeaverage access time Another measure : Another measure : data transfer ratedata transfer rate

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Access TimeAccess Time

The time needed The time needed to access data directlyto access data directly on disk on disk

Three primary factorsThree primary factors Seek timeSeek time Head switchingHead switching Rotational delayRotational delay

Average access timeAverage access time Usually measured Usually measured in millisecondsin milliseconds (ms) (ms) Current hard disk drives : Current hard disk drives : Under 10msUnder 10ms

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Data transferData transfer

The process of transferring data The process of transferring data between memory and the place on the between memory and the place on the disk trackdisk track WritingWriting : from memory to the track : from memory to the track ReadingReading : from the track to memory : from the track to memory

Data transfer rateData transfer rate Tells how fast data can be transferred once Tells how fast data can be transferred once

it has been foundit has been found Usually be measured in Usually be measured in megabytes of data megabytes of data

per secondper second

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Disk CacheDisk Cache

Used to improve the effective access Used to improve the effective access timetime

Memory cacheMemory cache