1. Information and Communication Technology Fundamentals
Credits Hours: 2+1
Instructor: Ayesha Bint Saleem

2. Storing Data Penning it down on a piece of paper
Typing it using typewriter and getting a hard copy
Storing it electronically on computer

3. Describing Storage Devices
Store data when computer is off
Re-use data at a later time
Two processes
Writing data
Recording data over some surface
Reading data
And transferring it to computer memory

4. Describing Storage Devices
Storage terms
Media is the physical material storing data
Storage devices manage the media
Writing data to storage device
Reading data from storage device
Diskette: storage medium, Diskette Drive: storage device
Magnetic Storage
Magnetic devices use a magnet
Optical Storage
Optical devices use lasers
Solid-state devices have physical switches

5. Magnetic Storage Devices
Most common form of storage
Hard drives, floppy drives, tape
All magnetic drives work the same
Similar Techniques for reading and writing
Surface of Storage media covered with Magnetically sensitive material
Reacts to magnetic field
Example; Iron Oxide
Teaching tip
Figure 6A.2 and 6A.3 on page 227 provide illustrations of devices and the read/write process.

6. Magnetic Storage Devices
Diskette
Single thin disk of plastic
Stores data on both sides
Each side has its own read/write head
Hard Disk
Contain multiple disks
Platters
Made of rigid material
Aluminum
Teaching tip
Figure 6A.2 and 6A.3 on page 227 provide illustrations of devices and the read/write process.

7. Magnetic Storage Devices
Floppy Disk
Hard Disk
Tape

8. Magnetic Storage Devices
One magnet makes another magnet
Stroke an iron bar with magnet in one direction
Use electrical current to polarize iron
Electromagnet
Polarity and strength dependant on direction and strength of current
Transistor stores a bit as ON or OFF
Orientation of Magnetic field used to represent data
Magnet can represent ON or OFF without continual source of electricity
Teaching tip
This process is difficult for students to see. Draw a diagram on the board that illustrates the process.

9. Magnetic Storage Devices
Data storage
Media is covered with iron oxide particles
Read/write head is an electro-magnet
Magnet writes charges on the media
Positive charge is a 1
Negative charge is a 0
Record 1s and 0s by alternating the direction of current
Teaching tip
This process is difficult for students to see. Draw a diagram on the board that illustrates the process.

10. Magnetic Storage Devices
Data retrieval
Read/Write head passes over surface while no current flows
Storage medium charges the Read/Write head
Small current flow with direction dependant on field polarity
Direction of flow is sensed and data is sent into memory
Teaching tip
This process is difficult for students to see. Draw a diagram on the board that illustrates the process.

11. Data Retrieval

12. Magnetic Storage Devices
Data organization
Disks must be formatted before use
Magnetically map disk surface
Assign addresses to different surface areas
Computer can go directly to required location: Random Access Nature
Reformatting destroys all data present on disk
Discussion point
Discuss the sector size limitation. Discuss what can happen when writing a 1-byte file or a 513-byte file. After the waste issue is brought up, then discuss the problem from the hardware issue. How can a manufacturer make a 1-byte head?

13. Magnetic Storage Devices
Data organization
Format draws tracks on the disk
Concentric rings
Numbered from outermost to innermost, starting from 0
Tracks is divided into sectors
Smallest unit Magnetic disk drive can work with
Entire sector read/written
In most Hard Disks a sector can store upto 512 bytes
All sectors on disk numbered in one long sequence
Each sector uniquely addressable and accessible
Discussion point
Discuss the sector size limitation. Discuss what can happen when writing a 1-byte file or a 513-byte file. After the waste issue is brought up, then discuss the problem from the hardware issue. How can a manufacturer make a 1-byte head?

14. Magnetic Storage Devices
Data organization
Outermost track longer than innermost track
Same number of sectors/track
All sectors store same amount of data
Don’t occupy same space
Waste of disk material; Longer tracks can store more data
Solution: More sectors to longer tracks
Move towards disk center; number of sectors/track ↓
More efficient method
Sectors/track given as average
Discussion point
Discuss the sector size limitation. Discuss what can happen when writing a 1-byte file or a 513-byte file. After the waste issue is brought up, then discuss the problem from the hardware issue. How can a manufacturer make a 1-byte head?

15. Tracks and Sectors

16. Magnetic Storage Devices
How OS finds data on disk
Each track and sector is labeled
Some are reserved
Location of all data kept in special log
Labeling called logical formatting
Different OS format disk in different ways
Different manner of data management on disk
Different File system
Teaching tip
Draw clustering on the board. Discuss why it can improve the performance of a system.

17. Magnetic Storage Devices
FAT file system
Standardized file allocation table to keep track of file locations on disk
Four areas created on disk
Boot Sector
Programs that run on startup, checks required files
Transfers control to OS that continues the process
Describes disk characteristics: bytes/sector, sectors/track
File Allocation Table
Log maintaining the location of each file +
status of sectors
Teaching tip
Draw clustering on the board. Discuss why it can improve the performance of a system.

18. Magnetic Storage Devices
Four areas created on disk
File Allocation Table
Writing to Disk: find open area using FAT  store file  log file ID + location
Reading: find location using FAT
Two copies of FAT, always kept updated
Root Folder
Master folder containing all other folders
Holds all the info about all other folders on disk
Data Area
Area where files and Programs are actually written
Teaching tip
Draw clustering on the board. Discuss why it can improve the performance of a system.

19. Magnetic Storage Devices
Finding data on disk
Listing of where files are stored
File Allocation Table (FAT)
FAT 16: MS-DOS, early Windows
FAT32
Extended edition of original FAT
Windows 95, 2000, XP
New Technology File System (NTFS)
Windows NT, supported by other Windows versions as well
Longer file names allowed
NTFS 5
High Performance File System (HPFS)
IBM OS/2
Teaching tip
Draw clustering on the board. Discuss why it can improve the performance of a system.

20. Magnetic Storage Devices
Finding data on disk
Sector grouped into clusters
Seen by OS as a single unit
Smallest place OS will allocate to a single file
Cluster sizes vary depending on size and type of disk
4 sectors (diskettes) ; 64 sectors (Hard disks)
Cluster usage tracked in FAT
Teaching tip
Draw clustering on the board. Discuss why it can improve the performance of a system.

21. Magnetic Storage Devices
Diskettes
Also known as floppy disks
Read with a disk drive
Mylar disk
Spin at 300 RPM
Amount of time required for one revolution 0.2 sec
Time to move from innermost to outermost track 0.17
Both happen simultaneously
Data access time = max(0.2, 0.17) = 0.2
0.5 sec if disk is moved from a dead stop
3 ½ floppy disk holds 1.44 MB
2880 sectors * 512 bytes/sector
Teaching tip
The formula for the disk capacity is listed on page 232 of the text.

22. Magnetic Storage Devices
Hard disks
Primary storage device in a computer
2 or more aluminum platters
Each platter has 2 sides
Spin between 5,400 to 15,000 RPM
Data found in 9.5 ms or less
Drive capacity greater than 40 GB
High rotational speed allows more data to be recorded
Faster movement can use smaller charges to make current flow through head
Teaching tip
Students often have a hard time grasping the speed of a hard drive. Use an analogy: The circumference of a hard drive platter is nearly 1 foot. A drive spinning 5,400 RPM can travel 5,400 feet in one minute, or a little over 1 mile in a minute!

23. Illustrated Hard Disk

24. Magnetic Storage Devices
Removable high capacity disks
Speed of hard disk
Portability of floppy disk
Several variants have emerged
High capacity floppy disk
Stores up to 750 MB of data
Hot swappable hard disks
Provide GB of data
Connect via USB

25. Magnetic Storage Devices
Tape drives
Best used for
Infrequently accessed data
Back-up solutions
Slow sequential access
Capacity exceeds 200 GB
To understand why random access hard drives and floppy drives are faster than sequential drives, compare the modern audio CD to the antiquated 8-track. On a CD if you wish to hear song 1 over and over, you simply press repeat. In an 8-track, you often must play the entire tape before the song can be repeated.

26. Optical Storage Devices
CD-ROM
Most software ships on a CD
Read using a laser
Lands, binary 1, reflect data
Pits scatter data
Written from the inside out
CD speed is based on the original
Original CD read 150 Kbps
A 10 X will read 1,500 Kbps
Speed slower than Hard Drive
Standard CD holds 650 MB

27. Optical Storage Devices
DVD-ROM
Digital Video Disk
Use both sides of the disk
Use layers
Capacities can reach 18 GB
DVD players can read CDs

28. Recordable Optical Technologies
CD Recordable (CD-R)
Create a data or audio CD
Data cannot be changed
Can continue adding until full

29. Recordable Optical Technologies
CD Re-Writable (CD-RW)
Create a reusable CD
Cannot be read in all CD players
Can reuse about 100 times
Insider Information
When a CD-R or RW is ‘burned’, the laser modifies the reflectivity of a dye that is sandwiched between the bottom clear layer and a top reflective layer. The lands are transparent sections while the pits are non-reflective.

30. Recordable Optical Technologies
Photo CD
Developed by Kodak
Provides for photo storage
Photos added to CD until full
Original pictures cannot be changed

31. Recordable Optical Technologies
DVD Recordable
Several different formats exist
None are standardized
Allows home users to create DVDs
Cannot be read in all players
There are several formats of DVD recordable. Current research indicates that DVD+R is more compatible with devices than the other formats. Spend time researching the different standards.

32. Recordable Optical Technologies
DVD-RAM
Allow reusing of DVD media
Not standardized
Cannot be read in all players

33. Solid State Devices Data is stored physically No magnets or laser
Less reliable and more expensive than Magnetic/Optical sotrage
Very fast
No mechanical motion invloved

34. Solid State Devices Flash memory Found in cameras and USB drives
Combination of RAM and ROM
Long term updateable storage

35. Solid State Devices Smart cards Credit cards with a chip
Chip stores data
Eventually may be used for cash
Hotels use for electronic keys

36. Solid State Devices Solid-state disks Large amount of SDRAM
Extremely fast
Volatile storage
Require battery backups
Most have hard disks copying data

37. Drive Performance Average access time Also known as seek time
Time to find desired data
Measured in milliseconds
Depends on two factors
RPM
Time to access a track
Average Access time half of maximum access time
Hard drive between 6 and 12 ms
CD between 80 and 800 ms
Tape drive slowest
Solid State fastest
To provide contrast, present the speed of memory as measured in the nanoseconds, or billionth of a second. Then discuss virtual RAM as defined earlier in the text. More RAM, less virtual RAM makes a faster machine.

38. Drive Performance Data transfer rate How fast data can be read
Measured in Bps or bps
Hard drive ranges from 15 to 160 MBps
CD ROMS depend on X factor
24x CD transfers 24 x 150 KBps
Floppy disks transfer at 45 KBps
Insider information
Most hard disks do not list the time to access a track. This is a good topic to tread lightly with.

39. Data Transfer Rate

40. Optimizing Performance
Disk optimization
Handled by operating system tool
Routine disk maintenance
Over time PC’s performance may slow down
Optimization should be run monthly

41. Optimizing Performance
Clean up unnecessary files
Delete temp files
Uninstall unused programs
Delete obsolete data files
Files should be cleaned weekly
Figure 6B.3 on page 249 shows the disk cleanup utility for Windows XP.

42. Optimizing Performance
Scan a disk for errors
Bad spots on the media
Unaccounted-for data
Find and fix the error
Move data to a good spot
Mark the spot as bad
Disks should be scanned monthly

43. Optimizing Performance
Defragment a disk
Files fragment when resaved
File does not occupy contiguous sectors when saved
Fragmented files load slower
Defragment puts the fragments together
Disks should be defragged monthly
Run scanning before defragmenting
Insider information
Windows 9x required the screen saver to be disabled before running scan or defrag. Failing to disable the screen saver could lead to catastrophic data loss!

44. Defragment

45. Optimizing Performance
File compression
Shrinks the size of a file
Takes up less space on disk
Resulting file called archive
Reduce a disks performance
Will increase disk capacity
PKZip, WinZip and WinRAR
MP3s are created using compression. If a audio song is recorded on a hard drive, the required storage is about 1 MB per second. When the MP3 compression is applied, the size is reduced to about 1 MB per minute.
Windows XP provides several compression routines. It provides for .zip file compression and archive creation. Zip archives can be accessed like normal folders. Folders can be compressed to shrink the contents. Finally, the entire disk can be compressed .

46. File Compression
763 KB on disk
Compressed
157 KB

47. Drive Interface Standards
How the device is connected
Drive controllers allow transfer of data
Dictates transfer rate and access time

48. Drive Interface Standards
Enhanced Integrated Drive Electronics
EIDE
Generic term for drive controllers
Several names
Fast IDE
Advanced Technology Attachment (ATA)
Up to 2 devices per controller
Most computers have 2 EIDE controllers
Insider Information
Serial ATA (SATA) is a newer standard aimed at replacing EIDE/ATA. SATA is quite fast and easy to use.

49. Drive Interface Standards
Small Computer System Interface
SCSI
Higher transfer rates than EIDE
More than 40 devices per SCSI controller
Computers may have several SCSI controllers
Many versions exist
Versions are typically incompatible
Found in servers and workstations
SCSI was introduced in chapter 5B of the text as a bus.

50. Drive Interface Standards
USB and FireWire
External drives
Transfer rate is limited
Many devices can be connected

51. End of Chapter