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Storage and Multimedia: The Facts and More

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Data is organized based upon access method. Organization method limits choice of storage medium ... Computer system may use both processing types based upon the ... – PowerPoint PPT presentation

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Title: Storage and Multimedia: The Facts and More


1
Storage and Multimedia The Facts and More
  • Chapter 6

2
Objectives
  • List the benefits of secondary storage
  • Identify and describe storage media available for
    personal computers
  • Differentiate among the principal types of
    secondary storage
  • Discuss the benefits of multimedia
  • Explain how data is organized, accessed, and
    processed

3
Contents
  • The Benefits of Secondary Storage
  • Magnetic Disk Storage
  • Logical Layout of a Disk
  • Disk Drive Operation
  • Optical Disk
  • Magnetic Tape Storage
  • Organizing and Accessing Data
  • Processing Stored Data
  • Applications

4
Secondary Storage Benefits
  • Semi-permanent
  • Non-volatile
  • Reliable
  • Convenient Locate and access data quickly

5
Secondary Storage Benefits
  • Compressed storage
  • Diskette about 500 printed pages
  • Optical disk about 500 books
  • Economy
  • Savings in physical storage costs
  • Savings in the speed and convenience of filing
    and retrieving data

6
Types of Storage
  • Magnetic Disk Storage
  • Optical Disks
  • Magneto-optical
  • CD-ROM
  • CD-R
  • CD-RW
  • DVD-ROM
  • Magnetic Tape Storage

7
Magnetic Disk Storage
  • Data represented as magnetic spots
  • Magnetized spot 1
  • Absence of a magnetized spot 0
  • Read
  • Converts the magnetized data to electrical
    impulses
  • Write
  • Converts electrical impulses to magnetized spots
    on disk

8
Disk Capacity
  • Size
  • MB
  • older hard disks
  • GB
  • current PC
  • TB
  • coming soon
  • Whats stored?
  • User documents
  • Software
  • Graphic images
  • Audio files
  • Video files

9
Diskettes
  • Low capacity small files
  • Portable
  • Flexible Mylar coated with metallic substance
  • Hard plastic jacket for protection
  • 3 ½ inch, 1.44 MB

10
High-Capacity Portable Disks
  • Larger files
  • Portable
  • High-capacity
  • 120 / 200 MB
  • Can read and write standard diskettes
  • Ex Superdisk
  • Zip disk
  • 250 MB
  • not compatible with 3 ½ inch diskettes

11
Data Compression
  • Why use?
  • Squeeze big files onto small disks
  • Speed up data transfer of files
  • Techniques
  • Remove all extra space characters
  • Substitutes a smaller data string for a
    frequently occurring set of characters
  • Software uses formula to determine how to
    compress
  • Must be decompressed

12
Hard Disk
  • Various sizes
  • Portability
  • Generally non-portable
  • Removable hard disks available for PC
  • Rigid platter coated with metallic substance

13
Disk Pack
  • Several platters
  • Airtight, sealed module
  • Mount disk pack on disk drive

14
Disk Pack
  • Disk pack has set of access arms
  • Two read / write heads per arm
  • One reads top surface
  • One reads bottom surface
  • Access arms move together as a unit
  • Only one read/write head works at a time

15
Logical Layout of a DiskTrack
  • Concentric circles
  • Passes under read/write head as disk rotates
  • 1.44 MB diskette has 80 tracks on each surface
  • Each track stores the same amount of data

16
Logical Layout of a DiskSector
  • Pie-shaped division of track
  • Holds a fixed number of bytes (512 bytes)
  • Cluster
  • Adjacent sectors treated as a unit of storage
  • Fixed number (2-8 sectors)
  • Minimum space allocated to a file

17
Logical Layout of a DiskCylinder
  • Same track on each platter
  • Store files across multiple platters
  • Reduces access time

18
Logical Layout of a DiskZone Recording
  • Assigns more sectors to tracks in outer zones
  • More sectors more data storage available

19
Disk DriveRead / Write Operation
  • Disks rotate
  • Access arm moves read/write head
  • Read / write operation begins and continues until
    complete
  • Data is transferred to/from memory

20
Access Time
  • Seek time
  • Head switching
  • Rotational delay
  • Data transfer rate

21
Data DestroyedHead Crash
22
Disk Caching
  • Required data read into memory
  • Adjacent data read into disk cache (special area
    of memory)
  • Program encounters a read instruction
  • Check disk cache
  • If present, no physical read is required
  • If not present, read from disk

23
RAID
Redundant Array of Independent Disks
24
Optical Disk
  • Greater capacity than other portable media
  • Process
  • Laser writes on metallic material spread over the
    surface of disk
  • Heat from laser produces pits on disk surface
  • Reading laser picks up light reflections from
    the pits
  • Technology
  • ROM
  • WORM

25
MOMagneto-optical
  • Hybrid
  • High-volume capacity
  • Written multiple times
  • Process
  • Laser melts a microscopic spot
  • Magnet aligns crystals
  • Reading laser picks up light reflection from
    crystals

26
CD-ROMCompact Disk Read-Only Memory
  • High capacity portable
  • Read multiple times
  • Cannot record
  • Capacity up to 680 MB (450 standard 3 ½ inch
    diskettes)
  • Used for software distribution

27
CD-RCompact Disc-Recordable
  • High capacity
  • Portable
  • Write once
  • Read multiple times
  • CD-R drive
  • CD-ROM drive

28
CR-RWCompact Disk-Rewritable
  • High capacity
  • Portable
  • Read multiple times
  • Record multiple times
  • Some compatibility problems reading CD-RW disks
    on CD-ROM drives

29
DVD-ROMDigital Versatile Disk
  • Larger capacity than CD-ROM
  • Standard Up to 4.7 GB, 7 times more than CD-ROM
  • Double layers 8.5 GB
  • Double-sided 17 GB
  • Data is packed more densely
  • Read multiple times, Cannot record
  • Can read CD-ROM disks

30
DVD-ROMDigital Versatile Disk
  • Benefits
  • Full-length movies
  • Audio quality comparable to audio compact disks
  • High-volume business data
  • Expected to replace CD-ROM in the near future

31
Magnetic Tape Storage
  • Plastic tape with magnetic coating
  • Capacity based on density bpi or cpi
  • Magnetic tape unit
  • Read/write head
  • Erase head erases previously recorded data
  • Inferior to disks
  • Not as reliable
  • Sequential access to data
  • Inexpensive
  • Primarily for backup

32
Backup Systems
  • Prevent data loss
  • Fire
  • Natural disaster
  • Electromechanical failures of disk
  • User introduced errors
  • Software errors
  • Accidental data deletion
  • Store data in more than one place

33
DataOrganizing and Accessing
  • Plan for way data is
  • Received
  • Organized
  • Stored
  • how it will be processed
  • Plan determined by programmer or systems analyst

34
DataGetting Organized
  • Character
  • Field
  • Record
  • File
  • Database

35
DataGetting Organized
  • Key Field
  • Unique identifier for a record

36
Data Access Methods
  • Application determines how data must be accessed
    by users
  • Data is organized based upon access method
  • Organization method limits choice of storage
    medium

37
Sequential
  • Records are stored and accessed in order
  • All records prior to the one requested must be
    read
  • Magnetic tape storage

38
Direct / Random Access
  • Records are not physically stored in any order
  • Go directly to the record to read
  • Hashing apply a formula to the key to produce
    the address of the record
  • Collision same address from different keys
  • Updating in place
  • Read, change, and return a record to the same
    place on disk
  • DASD Direct-Access Storage Device needed

39
Indexed
  • Records are stored sequentially
  • Index is generated that contains key and address
  • Can be read in order sequential
  • Can be read out of order random

40
Processing Stored Data
  • Batch
  • Transaction
  • Terminology
  • Transaction updates a record
  • Master file contains all the data

41
Processing Stored Data
42
Batch
  • Collect transactions into a transaction file and
    perform periodic updates
  • Process
  • Transactions are sorted by key field
  • Computer matches the master and transaction keys
  • Performs requested action add, revise, delete
  • New master file created
  • Error report is printed
  • Master file only current immediately after
    processing

43
Transaction
  • Processed upon request
  • Real-time process handled immediately
  • Disk storage
  • Direct access to desired record needed
  • Immediate access to stored data
  • Immediate updating of stored data

44
Batch and Transaction
  • Computer system may use both processing types
    based upon the application
  • Transaction
  • Activities relating to current needs
  • Batch
  • Updates per schedule

45
ApplicationsBank
  • Transaction
  • Check balance
  • Record cash withdrawal
  • Batch
  • Deposit left in the deposit drop
  • Bank statement

46
ApplicationsRetail POS
  • Transaction
  • Item price
  • Inventory updates as sale is made
  • Batch
  • Produce daily and weekly sales reports

47
ApplicationsMotor Vehicle
  • Transaction
  • Police check for stolen car report
  • Batch
  • Motor vehicle records of owner information

48
ApplicationsMultimedia
  • Hardware
  • CD-ROM or DVD-ROM
  • Sound card or sound chip
  • Speakers
  • MPEG
  • Video standards that support full-motion video
  • Faster drive provides faster data transfer and
    produces a smoother video

49
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