Chapter 6:Storage

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Chapter 6Storage

• Foundations for Interactivity,
• Multimedia, and Knowledge

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I. Storage Fundamentals

• Units of Measurement for Storage
• Kilobyte/Megabyte/Gigabyte/Terabyte
• Data Access Methods
• Sequential Storage
• magnetic tapes
• Direct Access Storage
• Harddisks, floppy disks, CD-ROMs

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II.Criteria for Rating Storage Devices

• Storage Capacity
• of bytes the disk can hold
• Access Speed
• the time needed to locate data
• Transfer Rate
• the speed at which data is transferred
• Removability
• the device that can be removed/installed
• Cost

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III. Diskettes

• The Disk Drive1. Read2. Write
• How A Disk Drive works
• Magnetic coating on the disk
• Read/Write head (R/W head)
• While disk spins, R/W head can read/write

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Cutaway view of a disk drive
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Diskettes

• C. Characteristics of Diskettes
• Tracks and Sectors
• track a circular band on the surface
• Sector
• Unformatted versus formatted disks
• Format define tracks and sectors
• Data capacitysides and densities
• Write-protect features

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Diskette anatomy
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IV. Hard Disks

• Hard-disks
• Multiple diskettes stacked in one pack.
• Each diskettes has its own R/W on both sides
• Hard-disk Connections
• SCSI Small Computer System Interface
• EIDE Enhanced Integrated Drive Electronics
• Fragmentation Defragmentation
• Cluster the unit the computer can access at a
  time from disk, multiple sectors
• Fragmentation a file spread out over many
  noncontiguous sectors

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Microcomputer hard-disk drive
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Multiple disks and cylinders
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D. Hard-Disks for Large Computer Systems

• Head crash
• When the R/W head contacts the surface of the
  disk
• Removable packs
• Fixed-disk drives
• RAID storage system

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V. Optical Disks 

• CD-ROM Disks
• Data is read/written through laser beams
• Single-speed 1x 150KB/Second, 150kbps
• 16x 2400kbps, 32x 4800kbps
• CD-R Disks Recording Your Own CDs
• Compact diskrecordable
• Compact disk - Recordable and reWriteable
• DVD The Digital Convergence Disk
• New generation of high-density CD-ROM

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Optical disks
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DVD versus CD-ROM
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Multilayered DVDs
With a dual-layer disk, the laser reads the
second layer of information by changing focus and
shining through the first layer