INTRODUCTION TO Data Storagefaculty.pucit.edu.pk/fakhra/IIT 2013/Lecture Notes/ITC Lecture 3.pdf · INTRODUCTION TO Data Storage ... system files are loaded from a hard disk into

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


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


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


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


High-CapacityRemovable Disks• Capacities greater

than 100 MB• Many uses

– Graphics, audio, orvideo

– Transporting files– Backups

• Zip drive


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


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 !


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


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


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”

INTRODUCTION TO Data Storagefaculty.pucit.edu.pk/fakhra/IIT 2013/Lecture Notes/ITC Lecture 3.pdf · INTRODUCTION TO Data Storage ... system files are loaded from a hard disk into

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