nanjing university of information sicence & technology competencies competencies primary...

NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGYNANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY

CompetenciesCompetencies primary storage and secondary storageprimary storage and secondary storage

Traditional floppy disk and high-capacity floppy disksTraditional floppy disk and high-capacity floppy disks

Internal hard disks, hard-disk cartridges and hard disk packsInternal hard disks, hard-disk cartridges and hard disk packs

How to improve hard-disk performance, such as disk caching, Raid, data How to improve hard-disk performance, such as disk caching, Raid, data

compression and decompressioncompression and decompression

Different types of optical discsDifferent types of optical discs

Solid-state storage, internal drives, and magnetic tapeSolid-state storage, internal drives, and magnetic tape

Mass storage and mass storage devicesMass storage and mass storage devices

Chapter 8 Secondary Storage


StorageStorage Primary storage devices: Primary storage devices: Memory, volatile or temporaryMemory, volatile or temporary

Secondary storage devicesSecondary storage devices

Provide permanent or nonvolatile storageProvide permanent or nonvolatile storage

Characteristics of secondary storage:Characteristics of secondary storage:

• MediaMedia

• CapacityCapacity

• Storage devicesStorage devices

• Access speedAccess speed


Floppy disksFloppy disks

portable and removable storage mediaportable and removable storage media

typically used to store and transfer relatively small data and filestypically used to store and transfer relatively small data and files

use flexible flat circular pieces of Mylar plastic that coated with a magnetic use flexible flat circular pieces of Mylar plastic that coated with a magnetic

materialmaterial

Floppy disk drives: Floppy disk drives:

used to store and read data which are represented by positive and negative used to store and read data which are represented by positive and negative

chargescharges

Traditional floppy disk: 1.44MB, 2HD 3.5inch diskTraditional floppy disk: 1.44MB, 2HD 3.5inch disk

2HD: 2HD: two-side, high-densitytwo-side, high-density

DensityDensity: how tightly the bits can be packed next to one another: how tightly the bits can be packed next to one another

Have a thin exterior jacket made of hard plastic to protect the inside flexible Have a thin exterior jacket made of hard plastic to protect the inside flexible

diskdisk


Metal ShutterMetal Shutter: can slide to one side to expose the recording surface(Data : can slide to one side to expose the recording surface(Data

access area)access area)

label: label: provide an area for users to write the contents of the diskprovide an area for users to write the contents of the disk

Write-protect notch: Write-protect notch:

have a slide that opens and closes.have a slide that opens and closes.

When is closed: When is closed: can either read data or save file to the disk can either read data or save file to the disk

When is opened: When is opened: file cannot be saved to the floppy diskfile cannot be saved to the floppy disk

Format: Format: should be formatted first before saving file to itshould be formatted first before saving file to it

• FormattingFormatting: segment the recording surface into tracks and sectors: segment the recording surface into tracks and sectors

• TracksTracks: concentric rings without visible grooves: concentric rings without visible grooves

• SectorsSectors: each track is divided into invisible wedge-shaped sections : each track is divided into invisible wedge-shaped sections

called sectors called sectors


High-capacity floppy disksHigh-capacity floppy disks

Also known as Also known as floppy disk cartridgesfloppy disk cartridges

Also 3.5 inches in diameterAlso 3.5 inches in diameter

however it is thicker, can store more information and requires special disk however it is thicker, can store more information and requires special disk

drives drives

Popular used high-capacity floppy disksPopular used high-capacity floppy disks

• Zip disk Zip disk produced by Iomega, typically has a 100MB, 250MB, or 750MB produced by Iomega, typically has a 100MB, 250MB, or 750MB

capacitycapacity


Hard disksHard disks

Also save files by altering the magnetic charges of the disk’s surfaceAlso save files by altering the magnetic charges of the disk’s surface

However use thicker, rigid metallic platters that are stacked one on top of anotherHowever use thicker, rigid metallic platters that are stacked one on top of another

Store and organize files using tracks, sectors, and cylindersStore and organize files using tracks, sectors, and cylinders

CylinderCylinder: a stack of overlapped platters: a stack of overlapped platters

Could store and retrieve information much faster and have a greater capacity Could store and retrieve information much faster and have a greater capacity

than floppy disks.than floppy disks.

Read/write head: Read/write head: Used to read or write information on a cushion of air without Used to read or write information on a cushion of air without

contacting the hard disk’s surfacecontacting the hard disk’s surface

Head CrashHead Crash: :

Head/write head makes contact with the hard disk’s surfaceHead/write head makes contact with the hard disk’s surface

It is a disaster for a hard disk which will destroy the data.It is a disaster for a hard disk which will destroy the data.


Internal Hard diskInternal Hard disk: :

Located in the system unit and usually being divided into different partitions, Located in the system unit and usually being divided into different partitions,

such as C drive, D drive, and so on.such as C drive, D drive, and so on.

Have fixed amount of storage and cannot be easily removed.Have fixed amount of storage and cannot be easily removed.

Mainly used to store operating system, application software and large files.Mainly used to store operating system, application software and large files.

Has two advantages over floppy disksHas two advantages over floppy disks

• Capacity: Capacity: 500GB, 700GB, 1000GB 500GB, 700GB, 1000GB

• Access speed:Access speed: the time required to find and retrieve information on the the time required to find and retrieve information on the

disk.disk.

Hard disk rotates very faster and the read/write head is close to the Hard disk rotates very faster and the read/write head is close to the

recording surface, it works much faster than floppy disks.recording surface, it works much faster than floppy disks.

To ensure adequate performance and security, routine maintenance and To ensure adequate performance and security, routine maintenance and

periodic backup should be performed.periodic backup should be performed.


Features of internal hard disksFeatures of internal hard disks

• Capacity: Capacity: 500GB, 700GB, 1000GB 500GB, 700GB, 1000GB

• Size: Size: 3.5inch(for desktop computer), 2.5inch(for laptop)3.5inch(for desktop computer), 2.5inch(for laptop)

• Rotational Speed: Rotational Speed: 5400RPM, 7200RPM, 10000RPM(Rotation Per Minute)5400RPM, 7200RPM, 10000RPM(Rotation Per Minute)

• Cache: Cache: 16MB, 32MB, 64MB16MB, 32MB, 64MB

• Interface:Interface:

IDE(PATA): IDE(PATA):

Data Transmission Rate: 100MB/s, 133MB/sData Transmission Rate: 100MB/s, 133MB/s

Rotational Speed: 5400RPM, 7200RPMRotational Speed: 5400RPM, 7200RPM

Serial ATA(SATA) : Serial ATA(SATA) :

Data Transmission Rate: SATA-1(150MB/s), SATA-2(300MB/s)Data Transmission Rate: SATA-1(150MB/s), SATA-2(300MB/s)


SCSI(SCSI(Small Computer System Interface): support hot swap): support hot swap

Data Transmission Rate: 320MB/sData Transmission Rate: 320MB/s



Hard Disk CartridgesHard Disk Cartridges

Can be removed easily, so can be used for protecting sensitive informationCan be removed easily, so can be used for protecting sensitive information

The number of cartridges can be expanded to increase the storage capacityThe number of cartridges can be expanded to increase the storage capacity

Mainly used to complement the internal hard disk and provide additional Mainly used to complement the internal hard disk and provide additional

capacitycapacity

Categories:Categories:

• Removable hard disksRemovable hard disks

• PC Card hard disksPC Card hard disks


Hard Disk PacksHard Disk Packs

Use more large platters aligned one above the other to store massive Use more large platters aligned one above the other to store massive

amounts of informationamounts of information

The pack is mounted onto special drivesThe pack is mounted onto special drives

The drive rotates the pack and access arm move in and out between the The drive rotates the pack and access arm move in and out between the

rotating platters.rotating platters.

Each access arm has two read/write heads, one reads the disk surface Each access arm has two read/write heads, one reads the disk surface

above it and the other read the disk surface below it.above it and the other read the disk surface below it.

All the access arms move in and out together. However, only one of the All the access arms move in and out together. However, only one of the

read/write head is activated at a moment.read/write head is activated at a moment.

A disk pack with 11 disks provides 20 recording surfaces, because the top A disk pack with 11 disks provides 20 recording surfaces, because the top

and bottom outside surfaces are not used.and bottom outside surfaces are not used.


Performance EnhancementPerformance Enhancement

Disk cachingDisk caching through hard disk cache through hard disk cache

• Hard disk cache acts as a temporary high-speed holding area between Hard disk cache acts as a temporary high-speed holding area between

the hard disk and the CPU.the hard disk and the CPU.

• Frequently used data is first detected and read from the hard disk into Frequently used data is first detected and read from the hard disk into

the cache. Then the data is accessed directly from cache to CPU when the cache. Then the data is accessed directly from cache to CPU when

needed.needed.

• The performance is increased since the transfer rate from memory is The performance is increased since the transfer rate from memory is

much faster than from the hard diskmuch faster than from the hard disk


RAID(Redundant Array of Inexpensive Disk)RAID(Redundant Array of Inexpensive Disk)

• Several inexpensive hard disks are connected to one another to provide Several inexpensive hard disks are connected to one another to provide

large amount of storage capacity.large amount of storage capacity.

• RAID technology and special RAID devices are used to connect or RAID technology and special RAID devices are used to connect or

group the hard disks together.group the hard disks together.

• can provide can provide large capacity, fast access speed and high reliabilitylarge capacity, fast access speed and high reliability

• Mainly used by Servers in large companies or organizationsMainly used by Servers in large companies or organizations


Levels RAID

• Level 1: Provides disk mirroring. Data written to one disk is mirrored to

second disk.

• Level 2: Bit-interleaved data. The data is interleaved across drives.

Check disks used to identify disk errors.

• Level 3: Bit-interleaved data with fewer check disks. Disk controller

detects errors, check disk recovers data.

• Level 4: Interleaved data, independent reads and writes. Spreading data

Transfer across disks provides higher performance.

• Level 5: Data and parity are spread over all disks. No check disk

required. Performance and useful storage capacity improved.


Stripe mirror Stripe+parity

Stripe+mirror


File compression and file decompressionFile compression and file decompression

• Reduce file size to save store capacityReduce file size to save store capacity

• Helps to speed up transmission of files over the InternetHelps to speed up transmission of files over the Internet

• Redundant information, such as repeating patterns in the file can be Redundant information, such as repeating patterns in the file can be

replace by a token.replace by a token.

• Some characteristic tokens should be kept so that the original file can Some characteristic tokens should be kept so that the original file can

be rebuilt or decompressed.be rebuilt or decompressed.

• Popular used software:Popular used software:

WinZipWinZip

WinRARWinRAR


Optical discsOptical discs

Two Laser Beams of the optical disc drive: Two Laser Beams of the optical disc drive: Read/WriteRead/Write

unlike the floppy disks and hard disks use the magnetic charges, optical discs unlike the floppy disks and hard disks use the magnetic charges, optical discs

use flat areas called use flat areas called landslands and bumpy areas called and bumpy areas called pitspits on the disc surface to on the disc surface to

represent 1s and 0srepresent 1s and 0s..

Optical discs only use concentric rings called tracks to record the information Optical discs only use concentric rings called tracks to record the information

Compact Disc(CD)Compact Disc(CD)

Popular Capacity: Popular Capacity: 640MB, 720MB640MB, 720MB

Three typesThree types

• Read only---Read only---CD-ROMCD-ROM(compact disc-read only memory): can’t write and (compact disc-read only memory): can’t write and

eraseerase

• Write once-Write once----CD-R (CD-recordable): ---CD-R (CD-recordable): can write oncecan write once

• RewritableRewritable--- CD-RW (compact disc rewritable, erasable optical discs):--- CD-RW (compact disc rewritable, erasable optical discs):

can erase and write for many timescan erase and write for many times


DVD (digital versatile disc or digital video disc)DVD (digital versatile disc or digital video disc)

Popular Capacity: Popular Capacity: from 4.7GB-17GBfrom 4.7GB-17GB

DVD ROM DriverDVD ROM Driver

Three typesThree types

• Read only---Read only---DVD-ROMDVD-ROM: can’t write and erase: can’t write and erase

• Two categories of DVD that can be write onceTwo categories of DVD that can be write once

DVD+R: DVD+R:

stands for recordable DVD proposed by Sony, Philips and HPstands for recordable DVD proposed by Sony, Philips and HP

DVD-R: DVD-R:

stands for write once DVD proposed by Pioneerstands for write once DVD proposed by Pioneer


High-definition DiscsHigh-definition Discs

DVD have sufficient capacity to record DVD have sufficient capacity to record standard-definitionstandard-definition movies and music, movies and music,

but they are insufficient to record but they are insufficient to record high-definition video.high-definition video.

The next generation of optical disc: The next generation of optical disc: hi def(high-definition disc)hi def(high-definition disc)

Two hi def discs:Two hi def discs:

• HD DVD(High definition DVD): HD DVD(High definition DVD):

have the capacity of 15 to 45 GBhave the capacity of 15 to 45 GB

• Blue-Ray (BDs):Blue-Ray (BDs):

a different format from DVD or HD DVD which need a special Blue-Ray a different format from DVD or HD DVD which need a special Blue-Ray

driverdriver

have the capacity of 25 to 50 GBhave the capacity of 25 to 50 GB

HD DVD and Blue-Ray Discs are not compatible with one another.HD DVD and Blue-Ray Discs are not compatible with one another.

Which will be the next-generation standard? Who knows?Which will be the next-generation standard? Who knows?


Other Types of Secondary StorageOther Types of Secondary Storage

Specialized storage: Specialized storage: solid-state storage, Internet hard drives and magnetic tapesolid-state storage, Internet hard drives and magnetic tape

Solid-state storage: Solid-state storage: have no moving parts and needn’t special drivers and have no moving parts and needn’t special drivers and

read/write heard.read/write heard.

Flash Memory cards: Flash Memory cards:

• high speed, easily removable, reliable, usually used for digital cameras.high speed, easily removable, reliable, usually used for digital cameras.

• Usually used to store images captured from digital video cameras and then Usually used to store images captured from digital video cameras and then

to transfer to the computers.to transfer to the computers.

• Some of the laptops have the Flash memory card port for card insertionSome of the laptops have the Flash memory card port for card insertion

• categories: categories: SD card, CF card, XD card, memory stick SD card, CF card, XD card, memory stick


USB drives: USB drives:

• Directly connect to a computer’s USB portDirectly connect to a computer’s USB port

• Usually have the capacities of 2GB, 4GB, 8GB, 16GB, and even 32GB and Usually have the capacities of 2GB, 4GB, 8GB, 16GB, and even 32GB and

64GB64GB

• Replacing the floppy disks due to the small size and high capacitiesReplacing the floppy disks due to the small size and high capacities


Internet Hard DrivesInternet Hard Drives

Special service sites on the Internet provide users with storagesSpecial service sites on the Internet provide users with storages

Internet hard driveInternet hard drive

Advantages:Advantages:

• Low costLow cost

• Flexibility to access information from any location using the InternetFlexibility to access information from any location using the Internet

Disadvantages:Disadvantages:

• Access speed is slower because all information must travel across the Access speed is slower because all information must travel across the

InternetInternet

• Security is a problem for Internet storageSecurity is a problem for Internet storage

• Unfit for storing high personalized and sensitive informationUnfit for storing high personalized and sensitive information

Some Internet Hard Drivers examples: iback, Xdrive and so onSome Internet Hard Drivers examples: iback, Xdrive and so on


Magnetic TapeMagnetic Tape

Two different access approaches to external storage Two different access approaches to external storage

• Direct access: Direct access:

Disks provide fast direct access. Disks provide fast direct access.

• Sequential access:Sequential access:

Tapes provide slower sequential access.Tapes provide slower sequential access.

Information is stored in sequenceInformation is stored in sequence

Searching must begin from the beginning one by one, which takes timeSearching must begin from the beginning one by one, which takes time

• Store data by altering the electromagnetic charges on the recording Store data by altering the electromagnetic charges on the recording

surface.surface.

• Although slower to access information, it is an effective and commonly Although slower to access information, it is an effective and commonly

used tool for backing up data.used tool for backing up data.

• Magnetic tape reels, tape cartridges or magnetic tape streamersMagnetic tape reels, tape cartridges or magnetic tape streamers


Mass Storage DevicesMass Storage Devices Mass storage refers to the tremendous amount of secondary storage required by Mass storage refers to the tremendous amount of secondary storage required by

large organizationslarge organizations

Mass storage devices are specialized high-capacity secondary storage devices Mass storage devices are specialized high-capacity secondary storage devices

used by large organizationsused by large organizations

Enterprise storage system: Promote efficient and safe used of data across the Enterprise storage system: Promote efficient and safe used of data across the

networks within the organizationsnetworks within the organizations

Support the following strategy:Support the following strategy:

File serversFile servers

Raid systemsRaid systems

Tape libraryTape library

DVD-ROM jukeboxesDVD-ROM jukeboxes

Organizational Internet storageOrganizational Internet storage

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