Transcript Slide 1
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 6A-3 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 6A-4 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 6A-5 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 6A-6 Magnetic Storage Devices Floppy Disk Hard Disk Tape 6A-7 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 6A-8 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 6A-9 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 6A-10 Data Retrieval 6A-11 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 6A-12 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 6A-13 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 6A-14 Tracks and Sectors 6A-15 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 6A-16 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 6A-17 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 6A-18 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 6A-19 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 6A-20 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 6A-21 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 6A-22 Illustrated Hard Disk 6A-23 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 6A-24 Magnetic Storage Devices • Tape drives • Best used for • Infrequently accessed data • Back-up solutions • Slow sequential access • Capacity exceeds 200 GB 6A-25 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 6A-26 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 6A-27 Recordable Optical Technologies • CD Recordable (CD-R) • Create a data or audio CD • Data cannot be changed • Can continue adding until full 6A-28 Recordable Optical Technologies • CD Re-Writable (CD-RW) • Create a reusable CD • Cannot be read in all CD players • Can reuse about 100 times 6A-29 Recordable Optical Technologies • Photo CD • Developed by Kodak • Provides for photo storage • Photos added to CD until full • Original pictures cannot be changed 6A-30 Recordable Optical Technologies • DVD Recordable • Several different formats exist • None are standardized • Allows home users to create DVDs • Cannot be read in all players 6A-31 Recordable Optical Technologies • DVD-RAM • Allow reusing of DVD media • Not standardized • Cannot be read in all players 6A-32 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 6A-33 Solid State Devices • Flash memory • Found in cameras and USB drives • Combination of RAM and ROM • Long term updateable storage 6A-34 Solid State Devices • Smart cards • Credit cards with a chip • Chip stores data • Eventually may be used for cash • Hotels use for electronic keys 6A-35 Solid State Devices • Solid-state disks • Large amount of SDRAM • Extremely fast • Volatile storage • Require battery backups • Most have hard disks copying data 6A-36 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 6B-37 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 6B-38 Data Transfer Rate 6B-39 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 6B-40 Optimizing Performance • Clean up unnecessary files • Delete temp files • Uninstall unused programs • Delete obsolete data files • Files should be cleaned weekly 6B-41 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 6B-42 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 6B-43 Defragment 6B-44 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 6B-45 File Compression 763 KB on disk Compressed 157 KB 6B-46 Drive Interface Standards • Interface • How the device is connected • Drive controllers allow transfer of data • Dictates transfer rate and access time 6B-47 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 6B-48 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 6B-49 Drive Interface Standards • USB and FireWire • External drives • Transfer rate is limited • Many devices can be connected 6B-50 End of Chapter