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
(No Transcript)