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

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

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

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

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.

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.

Magnetic Storage Devices Floppy Disk Hard Disk Tape

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.

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.

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.

Data Retrieval

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?

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?

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?

Tracks and Sectors

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.

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.

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.

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.

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.

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.

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!

Illustrated Hard Disk

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

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.

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

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

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

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.

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

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.

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

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

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

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

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

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.

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.

Data Transfer Rate

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

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.

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

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!

Defragment

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 .

File Compression 763 KB on disk Compressed 157 KB

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

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.

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.

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

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