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 Read Write
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 What’s stored? MB older hard disks GB current PC TB
coming soon
What’s 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? Techniques
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 Disk Track
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 Disk Sector
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 Disk Cylinder
Same track on each platter
Store files across multiple platters
Reduces access time

18. Logical Layout of a Disk Zone Recording
Assigns more sectors to tracks in outer zones
More sectors = more data storage available

19. Disk Drive Read / 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 Destroyed Head 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. MO Magneto-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-ROM Compact 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-R Compact Disc-Recordable
High capacity
Portable
Write once
Read multiple times
CD-R drive
CD-ROM drive

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

29. DVD-ROM Digital 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-ROM Digital 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 Store data in more than one place
Fire
Natural disaster
Electromechanical failures of disk
User introduced errors
Software errors
Accidental data deletion
Store data in more than one place

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

34. Data Getting Organized
Character
Field
Record
File
Database

35. Data Getting 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. Applications Bank Transaction Batch Check balance
Record cash withdrawal
Batch
Deposit left in the deposit drop
Bank statement

46. Applications Retail – POS
Transaction
Item price
Inventory updates as sale is made
Batch
Produce daily and weekly sales reports

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

48. Applications Multimedia
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