computers12 ch6
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Mongolia International University
Chapter 6Chapter 6
B.M.HB.M.H
Storage and Storage and MultimediaMultimedia
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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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MIUComputers
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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MIUComputers
Computer systemComputer system
Input Processing Output
SecondaryStorage
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MIUComputers
Secondary StorageSecondary Storage
Benefits Benefits SpaceSpace ReliabilityReliability ConvenienceConvenience Economy Economy
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MIUComputers
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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MIUComputers
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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MIUComputers
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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MIUComputers
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MIUComputers
Magnetic Disk StorageMagnetic Disk Storage
TypesTypes DiskettesDiskettes Hard disksHard disks
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MIUComputers
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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MIUComputers
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MIUComputers
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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MIUComputers
Hard DiskHard Disk
Disk packDisk pack assembles several plattersassembles several platters ComponentsComponents
Platters Access arms Read/write heads
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MIUComputers
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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MIUComputers
Data organization on a Data organization on a diskdisk
Several characteristicsSeveral characteristics TrackTrack SectorsSectors ClustersClusters Cylinder Cylinder
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MIUComputers
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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MIUComputers
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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MIUComputers
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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MIUComputers
Disk CacheDisk Cache
Used to improve the effective access Used to improve the effective access timetime
Memory cacheMemory cache