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Storage and Multimedia: The Facts and More. Chapter 6. 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 - PowerPoint PPT Presentation
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Storage and Multimedia: The Facts and More
Chapter 6
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
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
Secondary Storage Benefits
• Semi-permanent
• Non-volatile
• Reliable
• Convenient – Locate and access data quickly
• 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
Secondary Storage Benefits
Types of Storage
• Magnetic Disk Storage
• Optical Disks– Magneto-optical– CD-ROM– CD-R– CD-RW– DVD-ROM
• Magnetic Tape Storage
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
Disk Capacity
Size
MBolder hard disks
GBcurrent PC
TBcoming soon
What’s stored?
User documents
Software
Graphic images
Audio files
Video files
Diskettes
• Low capacity – small files
• Portable
• Flexible Mylar coated with metallic substance
• Hard plastic jacket for protection
• 3 ½ inch, 1.44 MB
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
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
Hard Disk
• Various sizes
• Portability– Generally non-portable– Removable hard disks available for PC
• Rigid platter coated with metallic substance
Disk Pack
Several platters
Airtight, sealed module
Mount disk pack on disk drive
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
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
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
• Same track on each platter
• Store files across multiple platters
• Reduces access time
Logical Layout of a DiskCylinder
Logical Layout of a DiskZone Recording
• Assigns more sectors to tracks in outer zones
• More sectors = more data storage available
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
Access Time
Seek time
Head switching
Rotational delay
Data transfer rate
Data DestroyedHead Crash
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
RAID
Redundant Array of Independent Disks
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
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
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
CD-RCompact Disc-Recordable
• High capacity
• Portable
• Write once
• Read multiple times– CD-R drive– CD-ROM drive
CR-RWCompact Disk-Rewritable
• High capacity
• Portable
• Read multiple times
• Record multiple times
• Some compatibility problems reading CD-RW disks on CD-ROM drives
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
• Benefits– Full-length movies– Audio quality comparable to audio compact
disks– High-volume business data
• Expected to replace CD-ROM in the near future
DVD-ROMDigital Versatile Disk
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
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
DataOrganizing and Accessing
• Plan for way data is– Received– Organized– Stored– how it will be processed
• Plan determined by programmer or systems analyst
DataGetting Organized
Character
Field
Record
File
Database
DataGetting Organized
Key Field
Unique identifier for a record
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
Sequential
• Records are stored and accessed in order
• All records prior to the one requested must be read
• Magnetic tape storage
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
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
Processing Stored Data
• Batch
• Transaction
• Terminology– Transaction – updates a record– Master file – contains all the data
Processing Stored Data
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
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
Batch and Transaction
• Computer system may use both processing types based upon the application
• Transaction– Activities relating to current needs
• Batch– Updates per schedule
ApplicationsBank
• Transaction– Check balance– Record cash withdrawal
• Batch– Deposit left in the deposit drop– Bank statement
ApplicationsRetail – POS
• Transaction– Item price– Inventory updates as sale is made
• Batch– Produce daily and weekly sales reports
ApplicationsMotor Vehicle
• Transaction– Police check for stolen car report
• Batch– Motor vehicle records of owner information
• 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
ApplicationsMultimedia