introduction to data storagefaculty.pucit.edu.pk/fakhra/iit 2013/lecture notes/itc lecture 3.pdf ·...
TRANSCRIPT
Introduction to Computing
INTRODUCTION TO
Data Storage
CPU AND MICROPROCESSORCPU AND MICROPROCESSOR
Memory• Used to store data, instructions, and
information– The operating system and other system
software– Application programs– Data being processed by application programs
• Bytes are stored at specific locations oraddresses
MemoryMemory
Memory• Size of memory is measured by the number
of bytes available
Memory
Memory• Volatile memory – contents are lost when
the computer is powered down• Nonvolatile memory – contents are not lost
when the computer is powered down
MemoryMemory
Random Access Memory (RAM)• The memory chips in the system unit• When the computer starts, operating
system files are loaded from a hard diskinto RAM
MemoryMemory
Random AccessMemory (RAM)• RAM Chips
– Smaller in size thanprocessor chips
– Packaged on circuitboards called singleinline memorymodules (SIMMs) ordual inline memorymodules (DIMMs)
MemoryMemory
Random Access Memory (RAM)• Configuring RAM
– The more RAM, the more programs and files acomputer can work on at once
– Software usually tells you how much RAM isrequired
– Necessary RAM depends on what type of workthe computer is used for
5A-30
Affecting Processing Speed
Virtual RAM• Computer is out of actual RAM• File that emulates RAM• Computer swaps data to virtual RAM
– Least recently used data is moved
5A-31
Memory
Nonvolatile memory• Holds data when power is off• Read Only Memory (ROM)• Basic Input Output System (BIOS)• Power On Self Test (POST)
MemoryMemory
Read-Only Memory (ROM)• Cannot be modified• Contents not lost when the computer
is turned off• PROM• EPROM• EEPROM
Bus
Address BusData BusBay
Cache MemoryHelps speed computer processes by storing frequently
used instructions and data Also called memory cache
5A-35
How Computers Process Data
Flash memory• Data is stored using physical switches• Special form of nonvolatile memory• Camera cards, USB key chains
5A-36
Affecting Processing Speed
The bus• Electronic pathway between components• Expansion bus connects to peripherals• System bus connects CPU and RAM• Bus width is measured in bits• Speed is tied to the clock
T e a c h e r s D i s c o v e r i n g C o m p u t e r s
Integrating Technologyin the Classroom3rd Edition
Secondary Storage
WHAT IS STORAGE?WHAT IS STORAGE?
The media on whichdata, instructions, andinformation are kept
The devices thatrecord and retrievedata, instructions, andinformation
Like a filing cabinet
WHAT IS STORAGE?WHAT IS STORAGE?
Storage Media and Devices• Storage medium
– Also called secondary storage– Physical material
• Storage device– Mechanism used to record and retrieve– Capacity measured in megabytes or gigabytes
Storage Devices
Floppy DiskHard DiskCD / DVDMiniature CardsSmart Cards
Floppy DisksWhat is a floppy disk drive?
p. 7.06 Fig. 7-6 Next
Floppy disk drive built intoa desktop computer
External floppy disk drive attaches toa computer with a cable
Also called secondary storage
One floppy drive, named drive A
If two floppy drives, seconddesignated as drive B
Device that reads from andwrites to floppy disk
WHAT IS STORAGE?WHAT IS STORAGE?
Floppy Disks• Portable, inexpensive
storage mediumconsisting of a thin,circular, flexible filmenclosed in a square-shaped plastic shell
• Several sizes– 8-inch– 5.25-inch– 3.5-inch
p. 7.05 Fig. 7-5
shutter
shell
liner
magneticcoating
flexible thin film
metal hub
Floppy DisksHow does a floppy disk drive work?
p. 7.06 Fig. 7-7 Next
Step 1. When you insert the floppy disk intodrive, shutter moves to the side to expose therecording surface on disk.
Step 2. When you initiate a diskaccess, circuit board on drive thatcontains electronics sends signals tocontrol movement of read/writeheads until they barely touchsurface (film) inside floppy disk’sshell.
Step 3. For writeinstructions, circuit boardverifies whether or not diskcan be written on.Step 4. Motor spins a
shaft, which causessurface inside floppydisk’s shell to spin.
Step 5. Motorpositions read/writeheads over correctlocation on recordingsurface of disk.
Step 6. Read/writeheads read datafrom and write dataon floppy disk.
Floppy Disks
p. 7.07 Fig. 7-8 Next
What are tracks and sectors?
Trackis narrowrecording bandthat forms fullcircle on disk
Sectorstores up to512 bytesof data
Formatting prepares disk for use and marks bad sectors asunusable
Click to view Web Link,then click Floppy Disksbelow Chapter 7
Floppy DisksHow do you compute a disk’s storage capacity?
p. 7.08 Next
Multiply number of sides, number of tracks, number of sectors pertrack, and number of bytes per sector For high-density disk: 2 sides 80 tracks 18 sectors per track 512
bytes per sector = 1,474,560 bytes
Characteristics of a3.5-inch High-DensityFloppy Disk
Capacity: 1.44 MB
Sides: 2
Tracks: 80
Sectors per track: 18
Sectors per disk: 2880
WHAT IS STORAGE?WHAT IS STORAGE?
Characteristics of a Floppy Disk• Uses magnetic patterns to store data• Formatting
– Track– Sector
• Write-protection• Guidelines for floppy disk care• Floppy disk drive
Floppy DisksWhat is a write-protect notch?
p. 7.08 Fig. 7-10 Next
Small opening with a cover that you slide Protects floppy disk from being erased accidentally
hole on thisside meansdisk is highdensity
write-protected
not write-protected
notch closedmeans youcan write onthe disk
notch openmeans youcannot writeon the disk
ExternalZip drive
Zip® Disks ®
What is a Zip disk?
p. 7.09 Fig. 7-11 Next
Magnetic medium that stores 100 MBor 250 MB of data or 750 MB
Zip disks require a Zip drivec—chighcapacity drive that reads from andwrites on a Zip disk
REV disks (35GB) are similar.
Used to back up and to transfer files Backup is duplicate of file, program, or
disk in case original is lostc
Zip disk
WHAT IS STORAGE?WHAT IS STORAGE?
High-CapacityRemovable Disks• Capacities greater
than 100 MB• Many uses
– Graphics, audio, orvideo
– Transporting files– Backups
• Zip drive
WHAT IS STORAGE?WHAT IS STORAGE?
Hard Disks• Provide large storage capacity and high
speed data access• Sizes range from 30 GB to 100 GB• Consists of several inflexible, circular disks,
called platters• Magnetic storage device• Formatting
Hard DisksHow does a hard disk work?
p. 7.11 Fig. 7-14 Next
Step 1.Circuit board controlsmovement of headactuator and a smallmotor.
Step 2.Small motor spinsplatters whilecomputer isrunning.
Step 3.When software requestsa disk access, read/writeheads determine currentor new location of data.
Step 4.Head actuator positionsread/write head arms overcorrect location onplatters to read or writedata.
Hard DisksWhat is a cylinder?
p. 7.11 Fig. 7-15 Next
Vertical section oftrack through allplatters
Single movementof read/write headarms accesses allplattersin cylinder
platter
read/writehead
platter
sides
cylinder
tracksector
Hard Disk Partitions andLogical DrivesWhen installing an operating system on a new
computer or after recovering from a hard diskfailure, prepare the hard disk for use by:• Partitioning the hard disk• Creating logical drives• Formatting logical drives• A maximum of 4 primary partitions can be placed
on a hard disk, but only 1 extended partition– The way the Master Boot Record is structured
determines this limitation.
Disk Partitioning
Partition disks to dividetotal storage spacePrimary partition — thesystem’s boot drive,used for system startupExtended partition —the remaining drivespace after you createthe primary partition
Logical Disk Drives
A disk partition mustbe assigned a logicaldrive identifierA primary partition istreated as a singlelogical driveAn extendedpartition can be dividedinto multiple logicaldrives (drives D and Ein figure)
Logical Drive Format
Low-level format:• Prepares the hard disk before disk partitions
can be defined• Primarily the responsibility of the hard disk
manufacturerHigh-level format:
• Logical drive formatting that prepares thedrive for use by the operating system
• Creates the file system root directory andthe files used to track disk space use
Hard DisksWhat are characteristics of a hard disk?
p. 7.10 Fig. 7-13 Next
Sample Hard Disk Characteristics
Advertised capacity 40 GBPlatters 2Read/write heads 4Cylinders 16,383Bytes per sector 512Sectors per track 63Sectors per drive 78,165,360Revolutions per minute 7,200Transfer rate 100 MB persecondAccess time 9 ms
actualdiskcapacity
Head Crash on a Hard DiskWhat is a head crash?
p. 7.12 Fig. 7-16 Next
clearance
read/write head
platter
hair
dustsmoke
Spinning creates cushion of air that floats read/write head above platter Occurs when read/write head touches platter surface
A smoke particle, dust particle, or human hair could render drive unusable Clearance between head and platter is approximately two-millionths of an
inch
hard disk
Next
Hard Disk CacheWhat is a disk cache?
p. 7.12 Fig. 7-17
Portion ofmemory thatprocessor usesto storefrequentlyaccessed items
second requestfor data—to HARD
disk
disk cache
first requestfor data—to disk cachein RAM
processor
SCSISCSI(Small(Small ComputerComputer SystemSystem Interface)Interface)controller supports up to fifteencontroller supports up to fifteendevices including hard disks, CDdevices including hard disks, CDand DVD drives, tape drives, printers,and DVD drives, tape drives, printers,scanners, network cardsscanners, network cards
SATASATA (Serial AdvancedSerial AdvancedTechnology Attachment) controllerTechnology Attachment) controlleruses serial signals to transfer data,uses serial signals to transfer data,instructions, and informationinstructions, and information
Magnetic Disk ControllersWhat is a disk controller?
p. 364 Next
EIDEEIDE (EnhancedEnhanced IntegratedIntegrated DriveDriveElectronics) controller supportsElectronics) controller supportsfour hard disks, providesfour hard disks, providesconnections for CD and DVDconnections for CD and DVDdrivesdrives
Chip and circuits thatChip and circuits thatcontrol transfer ofcontrol transfer ofitems from diskitems from disk
External Hard DisksWhat is an external hard disk ?
p. 7.13 Fig. 7-18 Next
External hard disk—freestandinghard disk that connects to system unit witha USB 2.0 cable
Used to back up or transfer files
Connects to USB 2.0 or Firewire port
Maxtor One-Touch Backup: 250GB,Cost: < $200.00 www.Seagate.com
Removable Magnetic DisksWhat are external hard disks and removable hard disks?
p. 364 Fig. 7-17 Next
External hard disk—freestandinghard disk that connects to system unit
Removable hard disk—hard diskthat you insert and removefrom hard disk drive
Used to back up or transfer files
Click to view WebLink, click Chapter 7, ClickWeb Link from leftnavigation, then clickHard Disksbelow Chapter 7
WHAT IS STORAGE?WHAT IS STORAGE?
CDs and DVDs• Optical storage media• Used to distribute software• Laser reads pits on the surface• Used on multimedia computers• Several types
– CD-ROM– DVD-ROM
CDs and DVDsHow does a laser read data on a CD or DVD?
p. 7.16 Fig. 7-21 Next
laserdiode
laserdiode
prism prism
light-sensingdiode
light-sensingdiode
0 1
lens lenspit land
disc label
Step 1.Laser diodeshines a lightbeam towarddisc.
Step 2.If light strikesa pit, itscatters. Iflight strikes aland, it isreflected backtoward diode.
Step 3.Reflected light isdeflected to alight-sensingdiode, whichsends digitalsignals of 1 tocomputer.Absence ofreflected light isread as digitalsignal of 0.
CDs and DVDsHow is data stored on a CD or
DVD?
p. 7.16 Fig. 7-22 Next
Typically stored insingle track
Track dividedinto evenlysized sectorsthat storeitems
Single trackspirals to edgeof disc
disc sectorsThe track on a DVD is 7.5 mileslong !
WHAT IS STORAGE?WHAT IS STORAGE?
Care of CDs and DVDs• Can last from 5 to 100 years if properly
cared for• Never bend a disc• Avoid extreme temperatures and humidity• Keep away from contaminants• Do not stack or touch discs• Use a protective case
WHAT IS STORAGE?WHAT IS STORAGE?
CD-ROM• Compact disc read-
only memory• Can contain text,
graphics, video, aswell as sound
• Can hold 650 MB ofdata
• Used for today’scomplex software
WHAT IS STORAGE?
CD-R and CD-RW• Compact disc-recordable
– Can write on each part of the disc only one time– Cannot be erased
• Compact disc-rewriteable– Can write on multiple times– Erasable disc
WHAT IS STORAGE?WHAT IS STORAGE?
DVD-ROM and DVD+RW• Digital video disc read-only memory (DVD-
ROM)– Can store from 4.7 GB to 17 GB– High quality– DVD-ROM drives– May replace CDs, VCRs, and VHS tapes
• Digital video disc+rewritable (DVD+RW)– Can write on multiple times– Erasable disc
WHAT IS STORAGE?
Miniature Mobile Storage Media
WHAT IS STORAGEWHAT IS STORAGE
External and Removable Hard Disks• External Hard Disk – Separate hard disk
that connects to a USB or FireWire port bycable– USB Drives
File System Types
Primary partitions and logical drivesmust be formatted so the operatingsystem can use themFormatting creates the file system by
adding information about how filesshould be stored on the drive toorganize and manage disk storageFile system types include:
• FAT 16, FAT32 and NTFS (Windows XP)• Ext3 and ReiserFS (Linux) created by Hans
Reiser– Note: Hans Reiser was on trial in Feb 2008 for murdering
his wife, Nina Reiser (from Russia). Reiser is/was acomputer programming genius entering Univ California atBerkeley at age 14
File and Directory Permissions
NTFS allows you to set permissionbits on system resourcesIn NTFS, you can protect files so that
only certain users or groups of userscan read themConcerns:
• If permissions are applied improperly,users may take security for granted
• Improperly set permissions can disruptan operating system
Disk Convert Utility
Information about the files on an NTFSvolume and their attributes is stored inthe MFTConvert utility — used to convert a
partition or logical drive from FAT orFAT32 to NTFS
convert drive /FS:NTFS[/v]
convert C: /FS:NTFS
Yes ! It works !
Disk Convert Utility
Information about the files on an NTFSvolume and their attributes is stored inthe MFTConvert utility — used to convert a
partition or logical drive from FAT orFAT32 to NTFS
convert drive /FS:NTFS[/v]
convert C: /FS:NTFS
Yes ! It works !
Disk Defragmenter Utility
As files are created and deleted, apartition can become severelyfragmentedFragmented files are no longer located
in contiguous clustersYou can use the Disk Defragmenter
utility to defragment hard disks and putfiles back together in a contiguousformat
Disk DefragmenterWhat is a Disk Defragmenter ?
Nextp. 8.17 Fig. 8-19
file before defragmentingfragmented diskfile afterdefragmenting
Reorganizes files and unused space intocontiguous sectors on hard disk so programsrun faster.
Chkdsk Utility
You can use the Chkdsk utility inWindows NT/2000/XP to:• Create and display a status report for a disk
based on its file system• List and correct errors on the disk• Display the status of the disk in the current
drive
• Click Start, click Run, type: chkdsk /F,Click OK
Disk Cleanup
Use the Disk Cleanup utility to recoverthe disk space used by:• Temporary files• Unused applications• Files in the Recycle Bin• Files you downloaded as part of Web
pages• Files created when Chkdsk attempted to
recover lost file fragments (e.g.FILE0001.CHK)
Push the same buttonto close the tray.
CDs and DVDsWhat are CDs and DVDs?
p. 7.15 Fig. 7-20 Next
Most PCs include CDor DVD drive, mostplay audio CDs
Flat, round, portablemetal discs withprotective plasticcoating
Can be read only orread/write
Insert the disc,label side up.
Push the button toslide out the tray.
Magnetic TapeHow is data stored on a tape?
p. 7. 24 Fig. 7-30 Next
Sequential access
Digital audio tape DAT 2 GB to 240 GBDigital linear tape DLT 20 GB to 220 GBLinear tape-open LTO 100 GB to 200 GBQuarter-inch cartridge QIC 40 MB to 25 GBTravan TR 8 GB to 40 GB
Popular Types of Tape
Name Abbreviation Storage Capacity
Unlike direct access — used on floppy disks, Zip disks,hard disks, CDs, and DVDs — which can locateparticular item immediately
Reads and writes data consecutively, like music tape
PC CardsWhat is a PC Card? (thickness is main difference)
p. 7.24 Figs. 7-31–7-32 Next
PC Cards
Category Thickness Use
Type I 3.3 mm RAM, SRAM, flashmemory
Type II 5.0 mm Modem, LAN, SCSI,sound, TV turner, harddisk, or other storage
Type III 10.5 mm Rotating storage suchas a hard disk
Adds capabilities to computer Credit-card-sized device commonly
used in notebook computers
Home-Task:Go throughChapter 7 of“DiscoveringComputers”