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Storage and Multimedia: The Facts and More

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

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Storage and Multimedia: The Facts and More

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  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. Size MB older hard disks GB current PC TB coming soon What’s stored? User documents Software Graphic images Audio files Video files Disk Capacity

  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

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