chapter 08-secondary storage
Post on 26-Oct-2014
138 Views
Preview:
TRANSCRIPT
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Ref Page Chapter 8: Secondary Storage Devices Slide 1/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Learning Objectives
In this chapter you will learn about:
Secondary storage devices and their need
Classification of commonly used secondary storagedevices
Difference betweenstorage devices
sequential and direct access
Basic principles of operation, types, and uses ofpopular secondary storage devices such as magnetictape, magnetic disk, and optical disk
(Continued on next slide)
Ref Page 117 Chapter 8: Secondary Storage Devices Slide 2/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Learning Objectives(Continued from previous slide..)
Commonly used mass storage devices
Introduction to other related concepts such as RAID,Jukebox, storage hierarchy, etc.
Ref Page 117 Chapter 8: Secondary Storage Devices Slide 3/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Limitations of Primary Storage
Limited capacity because the cost per bit of storageis high
Volatile - data stored in it is lost when the electricpower is turned off or interrupted
Ref Page 117 Chapter 8: Secondary Storage Devices Slide 4/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Secondary Storage
Used in a computer system to overcome the limitationsof primary storage
Has virtually unlimited capacity because the cost per bitof storage is very low
Has an operating speed far slower than that of theprimary storage
Used to store large volumes of data on a permanentbasis
Also known as auxiliary memory
Ref Page 117 Chapter 8: Secondary Storage Devices Slide 5/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Classification of Commonly Used SecondaryStorage Devices
Secondary StorageDevices
Sequential AccessDevice
Magnetic Tape
MagneticDisks
Direct Access Devices
Optical Disks Memory StorageDevices
FloppyDisk
HardDisks
CD-ROM WORM(CD-R)
CD-RW DVDFlashDrive
MemoryCard
Zip Disk Disk Pack Winchester Disk
Ref Page 118 Chapter 8: Secondary Storage Devices Slide 6/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Sequential-access Storage Devices
Arrival at the desired storage location may be precededby sequencing through other locations
Data can only be retrieved in the same sequence in whichit is stored
Access time varies according to the storage location ofthe information being accessed
Suitable for sequential processing applications wheremost, if not all, of the data records need to be processedone after another
Magnetic tape is a typical example of such a storagedevice
Ref Page 118 Chapter 8: Secondary Storage Devices Slide 7/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Direct-access Storage Devices
Devices where any storage location may be selectedand accessed at random
Permits access to individual information in a moredirect or immediate manner
Approximately equal access time is required foraccessing information from any storage location
Suitable for direct processing applications such as on-line ticket booking systems, on-line banking systems
Magnetic, optical, and magneto-optical disks aretypical examples of such a storage device
Ref Page 118 Chapter 8: Secondary Storage Devices Slide 8/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Tape Basics
Commonly used sequential-access secondary storagedevice
Physically, the tape medium is a plastic ribbon, whichis usually ½ inch or ¼ inch wide and 50 to 2400 feetlong
Plastic ribbon is coated with a magnetizable recordingmaterial such as iron-oxide or chromium dioxide
Data are recorded on the tape in the form of tinyinvisible magnetized and non-magnetized spots(representing 1s and 0s) on its coated surface
Tape ribbon is stored in reels or a small cartridge orcassette
Ref Page 119 Chapter 8: Secondary Storage Devices Slide 9/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Tape - Storage Organization(Example 1)
Track/Channel
numbers
0 12 3 4 5
Parity bit
Zone
7
6
5
4
Numeric 3
2
1
Illustrates the concepts of frames, tracks, parity bit, and character-by-character datastorage
Each vertical
line represents
a binary 1 bit
6 7 8 9 A
A frame Characters for
corresponding codes
B C D E F G
Ref Page 119 Chapter 8: Secondary Storage Devices Slide 10/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Tape Storage Capacity
Storage capacity of a tape =Data recording density x Length
Data recording density is the amount of data that can bestored on a given length of tape. It is measured in bytesper inch (bpi)
Tape density varies from 800 bpi in older systems to77,000 bpi in some of the modern systems
Actual storage capacity of a tape may be anywhere from35% to 70% of its total storage capacity, depending onthe storage organization used
Ref Page 120 Chapter 8: Secondary Storage Devices Slide 15/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Tape – Data Transfer Rate
Refers to characters/second that can be transmitted tothe memory from the tape
Transfer rate measurement unit is bytes/second (bps)
Value depends on the data recording density and thespeed with which the tape travels under the read/writehead
A typical value of data transfer rate is 7.7 MB/second
Ref Page 121 Chapter 8: Secondary Storage Devices Slide 16/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Tape – Tape Drive
Used for writing/reading of data to/from a magnetictape ribbon
Different for tape reels, cartridges, and cassettes
Has read/write heads for reading/writing of data ontape
A magnetic tape reel/cartridge/cassette has to be firstloaded on a tape drive for reading/writing of data on it
When processing is complete, the tape is removedfrom the tape drive for off-line storage
Ref Page 121 Chapter 8: Secondary Storage Devices Slide 17/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Tape – Tape Controller
Tape drive is connected to and controlled by a tapecontroller that interprets the commands for operating thetape drive
A typical set of commands supported by a tape controllerare:
Read
Write
Write tape header label
Erase tape
Back space one block
reads one block of data
writes one block of data
used to update the contents of tape header label
erases the data recorded on a tape
rewinds the tape to the beginning of previous block
(Continued on next slide)
Ref Page 121 Chapter 8: Secondary Storage Devices Slide 18/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Magnetic Tape
½-inch tape reel
½-inch tape cartridge
¼-inch streamer tape
4-mm digital audio tape (DAT)
Ref Page 121 Chapter 8: Secondary Storage Devices Slide 20/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Magnetic Tapes
Storage capacity is virtually unlimited because as manytapes as required can be used for storing very largedata sets
Cost per bit of storage is very low for magnetic tapes.
Tapes can be erased and reused many times
Tape reels and cartridges are compact and light inweight
Easy to handle and store.
Very large amount of data can be stored in a smallstorage space
(Continued on next slide)
Ref Page 123 Chapter 8: Secondary Storage Devices Slide 31/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Magnetic Tapes(Continued from previous slide..)
Compact size and light weight
Magnetic tape reels and cartridges are also easilyportable from one place to another
Often used for transferring data and programs fromone computer to another that are not linked together
Ref Page 123 Chapter 8: Secondary Storage Devices Slide 32/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Limitations of Magnetic Tapes
Due to their sequential access nature, they are notsuitable for storage of those data that frequentlyrequire to be accessed randomly
Must be stored in a dust-free environment becausespecks of dust can cause tape-reading errors
Must be stored in an environment with properlycontrolled temperature and humidity levels
Tape ribbon may get twisted due to warping, resultingin loss of stored data
Should be properly labeled so that some useful datastored on a particular tape is not erased by mistake
Ref Page 123 Chapter 8: Secondary Storage Devices Slide 33/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Uses of Magnetic Tapes
For applications that are based on sequential dataprocessing
Backing up of data for off-line storage
Archiving of infrequently used data
Transferring of data from one computer to another thatare not linked together
As a distribution media for software by vendors
Ref Page 124 Chapter 8: Secondary Storage Devices Slide 34/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk - Basics
Commonly used direct-access secondary storage device.
Physically, a magnetic disk is a thin, circularplate/platter made of metal or plastic that is usuallycoated on both sides with a magnetizable recordingmaterial such as iron-oxide
Data are recorded on the disk in the form of tinyinvisible magnetized and non-magnetized spots(representing 1s and 0s) on the coated surfaces of thedisk
The disk is stored in a specially designed protectiveenvelope or cartridge, or several of them are stackedtogether in a sealed, contamination-free container
Ref Page 124 Chapter 8: Secondary Storage Devices Slide 35/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Storage OrganizationIllustrates the Concept of Tracks
200Tracks
Track 000 A disk’s surface is divided into
a number of invisibleconcentric circles called tracks
The tracks are numberedconsecutively from outermostto innermost starting fromzero
The number of tracks on adisk may be as few as 40 onsmall, low-capacity disks, toseveral thousand on large,high-capacity disks
… Track199
…
Ref Page 125 Chapter 8: Secondary Storage Devices Slide 36/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Storage OrganizationIllustrates the Concept of Sectors
A sector
Each track of a disk issubdivided into sectors
There are 8 orsectors per track
more
A sector typically contains512 bytes
Disk drives are designed toread/write only wholesectors at a time
Ref Page 125 Chapter 8: Secondary Storage Devices Slide 37/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Storage Organization
Illustrates Grouping of Tracks and Use of DifferentNumber of Sectors in Tracks of Different Groups for
Increased Storage Capacity
Innermost group of trackshas 8 sectors/track
Next groups of tracks has9 sectors/track
Outermost group of trackshas 10 sectors/track
Ref Page 125 Chapter 8: Secondary Storage Devices Slide 38/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Disk Address orAddress of a Record on a Disk
Disk address represents the physical location of therecord on the disk
It is comprised of the sector number, track number,and surface number (when double-sided disks areused)
This scheme is called the CHS addressing or Cylinder-Head-Sector addressing. The same is also referred toas disk geometry
Ref Page 126 Chapter 8: Secondary Storage Devices Slide 39/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Storage Organization(Illustrates the Concept of Cylinder)
Upper surfacenot used
Surface - 0Surface - 1
Surface - 2
Surface - 3
Surface - 4Surface - 5
Lower surfacenot used
No. of disk platters = 4, No. of usable surfaces = 6. A set of correspondingtracks on all the 6 surfaces is called a cylinder.
Central shaft
Read/Write head
Direction ofmovement ofaccess armsassembly
Cylinder
Access armsassembly
Ref Page 127 Chapter 8: Secondary Storage Devices Slide 40/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Storage Capacity
Storage capacity of a disk system = Number of recording surfaces Number of tracks per surface Number of sectors per track Number of bytes per sector
Ref Page 126 Chapter 8: Secondary Storage Devices Slide 41/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk Pack – Access Mechanism
One read/writehead per surface Central shaft
Direction ofmovement ofaccess armsassembly
Access armsassembly
Vertical cross section of a disk system. There is one read/write head perrecording surface
Ref Page 127 Chapter 8: Secondary Storage Devices Slide 42/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Access Time
Disk access time is the interval between the instant acomputer makes a request for transfer of data from adisk system to the primary storage and the instant thisoperation is completed
Disk access time depends on the following threeparameters:
– Seek Time: It is the time required to position theread/write head over the desired track, as soon asa read/write command is received by the disk unit
– Latency: It is the time required to spin the desiredsector under the read/write head, once theread/write head is positioned on the desired track
Ref Page 128 Chapter 8: Secondary Storage Devices Slide 43/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Access Time
– Transfer Rate: It is the rate at which data areread/written to the disk, once the read/write headis positioned over the desired sector
As the transfer rate is negligible as compared to seektime and latency,
Average access time
= Average seek time + Average latency
Ref Page 128 Chapter 8: Secondary Storage Devices Slide 44/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Disk Formatting
Process of preparing a new disk by the computersystem in which the disk is to be used.
For this, a new (unformatted) disk is inserted in the diskdrive of the computer system and the disk formattingcommand is initiated
Low-level disk formatting
Disk drive’s read/write head lays down a magneticpattern on the disk’s surface
Enables the disk drive to organize and store thedata in the data organization defined for the diskdrive of the computer
(Continued on next slide)
Ref Page 129 Chapter 8: Secondary Storage Devices Slide 45/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Disk Formatting(Continued from previous slide..)
OS-level disk formatting
Creates the File Allocation Table (FAT) that is atable with the sector and track locations of data
Leaves sufficient space for FAT to grow
Scans and marks bad sectors
One of the basic tasks handled by the computer’soperating system
Enables the use of disks manufactured by third partyvendors into one’s own computer system
Ref Page 129 Chapter 8: Secondary Storage Devices Slide 46/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Disk Drive(Continued from previous slide..)
Although disk drives vary greatly in their shape, sizeand disk formatting pattern, they can be broadlyclassified into two types:
– Those with interchangeable magnetic disks,which allow the loading and unloading ofmagnetic disks as and when they are needed forreading/writing of data on to them
– Those with fixed magnetic disks, which comealong with a set of permanently fixed disks. Thedisks are not removable from their disk drives
Ref Page 129 Chapter 8: Secondary Storage Devices Slide 48/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Magnetic Disk – Disk Controller
Disk drive is connected to and controlled by a diskcontroller, which interprets the commands foroperating the disk drive
Typically supports only read and write commands,which need disk address (surface number,cylinder/track number, and sector number) asparameters
Connected to and controls more than one disk drive, inwhich case the disk drive number is also needed as aparameters of read and write commands
Ref Page 130 Chapter 8: Secondary Storage Devices Slide 49/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Magnetic Disks
Magnetic Disks
Floppy Disks Hard Disks
Zip/Bernoulli Disks Disk Packs WinchesterDisks
Ref Page 130 Chapter 8: Secondary Storage Devices Slide 50/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Floppy Disks
Round, flat piece of flexible plastic disks coated withmagnetic oxide
So called because they are made of flexible plasticplates which can bend
Also known as floppies or diskettes
Plastic disk is encased in a square plastic or vinyl jacketcover that gives handling protection to the disk surface
(Continued on next slide)
Ref Page 130 Chapter 8: Secondary Storage Devices Slide 51/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Floppy Disks(Continued from previous slide..)
The two types of floppy disks in use today are:
5¼-inch diskette, whose diameter is 5¼-inch.It is encased in a square, flexible vinyl jacket
3½-inch diskette, whose diameter is 3½-inch.It is encased in a square, hard plastic jacket
Most popular and inexpensive secondary storagemedium used in small computers
Ref Page 131 Chapter 8: Secondary Storage Devices Slide 52/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
A 5¼-inch Floppy Disk
Manufacturer’slabel
User’s label foridentification purpose
Write protect notch
Drive spindlehole in disk
Drive access openingin jacket
Aperture in the jacketthrough which theread/write head makesdirect contact with thedisk surface
5¼ - inch
A 5¼-inch floppy disk enclosed within jacket. The drive mechanism clampson to a portion of the disk exposed by the drive access opening in the jacket
Ref Page 131 Chapter 8: Secondary Storage Devices Slide 53/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
A 3½-inch Floppy Disk
Light indicator(blinks whenread/writeoperation takesplace) (a) Front view of a floppy disk
drive.
Opening for inserting thedisk inside the drive
Floppy diskeject button
Write-protectplastic tab
3½” - inch
(b) A 3½ - inch floppy disk.
Ref Page 131 Chapter 8: Secondary Storage Devices
Sliding metalpiece cover
User’s label foridentification
Slide 54/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Storage Capacities of Various Types of FloppyDisks
Size(Diameterin inches)
No. ofsurfaces
No. oftracks
No. ofsectors/track
No. ofbytes/sector
512
512
512
512
512
Capacityin bytes
Approximatecapacity
360 KB
1.2 MB
720 KB
1.4 MB
2.88 MB
5¼
5¼
3½
3½
3½
2
2
2
2
2
40
80
40
80
80
9
15
18
18
36
3,68,640
12,28,800
7,37,280
14,74,560
29,49,120
Ref Page 131 Chapter 8: Secondary Storage Devices Slide 55/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Hard Disks
Round, flat piece of rigid metal (frequently aluminium)disks coated with magnetic oxide
Come in many sizes, ranging from 1 to 14-inchdiameter.
Depending on how they are packaged, hard disks are ofthree types:
Zip/Bernoulli disks
Disk packs
Winchester disks
Primary on-line secondary storage device for mostcomputer systems today
Ref Page 132 Chapter 8: Secondary Storage Devices Slide 56/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Zip/Bernoulli Disks
Uses a single hard disk platter encased in a plasticcartridge
Disk drives may be portable or fixed type
Fixed type is part of the computer system, permanentlyconnected to it
Portable type can be carried to a computer system,connected to it for the duration of use, and then can bedisconnected and taken away when the work is done
Zip disks can be easily inserted/removed from a zip drivejust as we insert/remove floppy disks in a floppy diskdrive
Ref Page 132 Chapter 8: Secondary Storage Devices Slide 57/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Disk Packs
Uses multiple (two or more) hard diskmounted on a single central shaft
platters
Disk drives have a separate read/write head for eachusable disk surface (the upper surface of the top-mostdisk and the lower surface of the bottom most disk isnot used)
Disks are of removable/interchangeable type in thesense that they have to be mounted on the disk drivebefore they can be used, and can be removed andkept off-line when not in use
Ref Page 132 Chapter 8: Secondary Storage Devices Slide 58/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Winchester Disks
Uses multiple (two or more) hard disk plattersmounted on a single central shaft
Hard disk platters and the disk drive are sealedtogether in a contamination-free container and cannotbe separated from each other
(Continued on next slide)
Ref Page 132 Chapter 8: Secondary Storage Devices Slide 59/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Winchester Disks(Continued from previous slide..)
For the same number of disks, Winchester disks havelarger storage capacity than disk packs because:
– All the surfaces of all disks are used for datarecording
They employ much greater precision of data recording,resulting in greater data recording density
Named after the .30-30 Winchester rifle because theearly Winchester disk systems had two 30-MB diskssealed together with thedisk drive
Ref Page 132 Chapter 8: Secondary Storage Devices Slide 60/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Magnetic Disks
More suitable than magnetic tapes for a wider range ofapplications because they support direct access of data
Random access property enables them to be usedsimultaneously by multiple users as a shared device. Atape is not suitable for such type of usage due to itssequential-access property
Suitable for both on-lineand off-line storage of data
(Continued on next slide)
Ref Page 133 Chapter 8: Secondary Storage Devices Slide 61/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Magnetic Disks(Continued from previous slide..)
Except for the fixed type Winchester disks, the storagecapacity of other magnetic disks is virtually unlimitedas many disks can be used for storing very large datasets
Due to their low cost and high data recording densities,the cost per bit of storage is low for magnetic disks.
An additional cost benefit is that magnetic disks can beerased and reused many times
Floppy disks and zip disks are compact and light inweight. Hence they are easy to handle and store.
Very large amount of data can be stored in a smallstorage space
(Continued on next slide)
Ref Page 133 Chapter 8: Secondary Storage Devices Slide 62/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Magnetic Disks
Due to their compact size and light weight, floppy disksand zip disks are also easily portable from one place toanother
They are often used for transferring data and programsfrom one computer to another, which are not linkedtogether
Any information desired from a disk storage can beaccessed in a few milliseconds because it is a directaccess storage device
(Continued on next slide)
Ref Page 133 Chapter 8: Secondary Storage Devices Slide 63/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Magnetic Disks(Continued from previous slide..)
Data transfer rate for a magnetic disk system isnormally higher than a tape system
Magnetic disks are less vulnerable to data corruptiondue to careless handling or unfavorable temperatureand humidity conditions than magnetic tapes
Ref Page 133 Chapter 8: Secondary Storage Devices Slide 64/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Limitations of Magnetic Disks
Although used for both random processing andsequential processing of data, for applications of thelatter type, it may be less efficient than magnetictapes
More difficult to maintain the security of informationstored on shared, on-line secondary storage devices,as compared to magnetic tapes or other types ofmagnetic disks
(Continued on next slide)
Ref Page 134 Chapter 8: Secondary Storage Devices Slide 65/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Limitations of Magnetic Disks(Continued from previous slide..)
For Winchester disks, a disk crash or drive failure oftenresults in loss of entire stored data. It is not easy torecover the lost data. Suitable backup procedures aresuggested for data stored on Winchester disks
Some types of magnetic disks, such as disk packs andWinchester disks, are not so easily portable likemagnetic tapes
On a cost-per-bit basis, the cost of magnetic disks islow, but the cost of magnetic tapes is even lower
(Continued on next slide)
Ref Page 134 Chapter 8: Secondary Storage Devices Slide 66/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Limitations of Magnetic Disks(Continued from previous slide..)
Must be stored in a dust-free environment
Floppy disks, zip disks and disk packs should belabeled properly to prevent erasure of useful data bymistake
Ref Page 134 Chapter 8: Secondary Storage Devices Slide 67/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Uses of Magnetic Disks
For applications that are based on random dataprocessing
As a shared on-line secondary storage device.Winchester disks and disk packs are often used forthis purpose
As a backup device for off-line storage of data. Floppydisks, zip disks, and disk packs are often used for thispurpose
(Continued on next slide)
Ref Page 134 Chapter 8: Secondary Storage Devices Slide 68/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Uses of Magnetic Disks(Continued from previous slide..)
Archiving of data not used frequently, but may beused once in a while. Floppy disks, zip disks, anddisk packs are often used for this purpose
Transferring of data and programs from onecomputer to another that are not linked together.Floppy disks and zip disks are often used for thispurpose
Distribution of software by vendors. Originally soldsoftware or software updates are often distributed byvendors on floppy disks and zip disks
Ref Page 134 Chapter 8: Secondary Storage Devices Slide 69/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Optical Disk – Basics
Consists of a circular disk, which is coated with a thinmetal or some other material that is highly reflective
Laser beam technology is used for recording/readingof data on the disk
Also known as laser disk / optical laser disk, due tothe use of laser beam technology
Proved to be a promising random access medium forhigh capacity secondary storage because it can storeextremely large amounts of data in a limited space
Ref Page 134 Chapter 8: Secondary Storage Devices Slide 70/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Optical Disk – Storage Organization
Has one long spiral track, which starts at the outer edgeand spirals inward to the center
Track is divided into equal size sectors
(a) Track pattern on an optical disk (b) Track pattern on a magnetic disk
Difference in track patterns on optical and magnetic disks.
Ref Page 135 Chapter 8: Secondary Storage Devices Slide 71/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Optical Disk – Storage Capacity
Storage capacity of an optical disk
= Number of sectors Number of bytes per sector
The most popular optical disk uses a disk of 5.25 inchdiameter with storage capacity of around 650 Megabytes
Ref Page 135 Chapter 8: Secondary Storage Devices Slide 72/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Optical Disk – Access Mechanism
Laserbeamsource
Laserbeamsource
Prism
SensorLaser beam getsscattered by a pit(represents 0)
LandPit Pit
Prism
SensorLaser beam getsreflect by a land(represents1)
LandLand
Pit
Ref Page 136 Chapter 8: Secondary Storage Devices Slide 73/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Optical Disk – Access Time
With optical disks, each sector has the same lengthregardless of whether it is located near or away fromthe disk’s center
Rotation speed of the disk must vary inversely withthe radius. Hence, optical disk drives use a constantlinear velocity (CLV) encoding scheme
Leads to slower data access time (larger access time)for optical disks than magnetic disks
Access times for optical disks are typically in therange of 100 to 300 milliseconds and that of harddisks are in the range of 10 to 30 milliseconds
Ref Page 137 Chapter 8: Secondary Storage Devices Slide 74/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Optical Disk Drive
Uses laser beam technology for reading/writing of data
Has no mechanical read/write access arm
Uses a constant linear velocity (CLV) encoding scheme,in which the rotational speed of the disk varies inverselywith the radius
Ref Page 136 Chapter 8: Secondary Storage Devices Slide 75/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Optical Disk Drive
Lightindicator
Volume control button usedwhen the drive is used toplay a music CD
Optical disk
A headphone socketenables the user toplug-in head-phonesand listen to recordedsound when the driveis used to play musicCDs.
Is placed ontop of thisgroove
Tray eject Direction ofbutton movement of
the trayOptical disk tray
Ref Page 137 Chapter 8: Secondary Storage Devices Slide 76/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Optical Disks
The types of optical disks in use today are:
CD-ROM
Stands for Compact Disk-Read Only Memory
Packaged as shiny, silver color metal disk of 5¼inch (12cm) diameter, having a storage capacity ofabout 650 Megabytes
Disks come pre-recorded andstored on them cannot be altered
the information
Pre-stamped (pre-recorded) by their suppliers, by aprocess called mastering
(Continued on next slide)
Ref Page 138 Chapter 8: Secondary Storage Devices Slide 77/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Optical Disks(Continued from previous slide..)
Provide an excellent medium to distribute largeamounts of data in electronic dorm at low cost.
A single CD-ROM disk can hold a completeencyclopedia, or a dictionary, or a world atlas, orbiographies of great people, etc
Used for distribution of electronic version ofconference proceedings, journals, magazines,books, and multimedia applications such as videogames
Used by software vendors for distribution ofsoftware to their customers
Ref Page 138 Chapter 8: Secondary Storage Devices Slide 78/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Optical Disks
WORM Disk / CD-Recordable (CD-R)
Stands for Write Once Read Many. Data can be writtenonly once on them, but can be read many times
Same as CD-ROM and has same storage capacity
Allow users to create their own CD-ROM disks by usinga CD-recordable (CD-R) drive that can be attached toa computer as a regular peripheral device
Data to be recorded can be written on its surface inmultiple recording sessions
(Continued on next slide)
Ref Page 138 Chapter 8: Secondary Storage Devices Slide 79/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Optical Disks(Continued from previous slide..)
Sessions after the first one are always additiveand cannot alter the etched/burned information ofearlier sessions
Information recorded on them can be read by anyordinary CD-ROM drive
They are used for data archiving and for making apermanent record of data. For example, manybanks use them for storing their daily transactions
Ref Page 138 Chapter 8: Secondary Storage Devices Slide 80/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Optical Disks
CD-Read/Write (CD-RW)
Same as CD-R and has same storage capacity
Allow users to create their own CD-ROM disks byusing a CD-recordable (CD-R) drive that can beattached to a computer as a regular peripheraldevice
Data to be recorded can be written on its surface inmultiple recording sessions
Made of metallic alloy layer whose chemicalproperties are changed during burn and erase
Can be erased and written afresh
Ref Page 138 Chapter 8: Secondary Storage Devices Slide 81/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Types of Optical Disks
Digital Video / Versatile Disk (DVD)
Looks same as CD-ROM but has capacity of 4.7 GB or8.5 GB
Designed primarily to store and distribute movies
Can be used for storage of large data
Allows storage of video in 4:3 or 16:9 aspect-ratios inMPEG-2 video format using NTSC or PAL resolution
Audio is usually Dolby® Digital (AC-3) or DigitalTheater System (DTS) and can be either monaural or5.1 Surround Sound
Ref Page 138 Chapter 8: Secondary Storage Devices Slide 82/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Optical Disks
The cost-per-bit of storage for optical disks is very lowbecause of their low cost and enormous storage density.
The use of a single spiral track makes optical disks an idealstorage medium for reading large blocks of sequential data,such as music.
Optical disk drives do not have any mechanical read/writeheads to rub against or crash into the disk surface. Thismakes optical disks a more reliable storage medium thanmagnetic tapes or magnetic disks.
Optical disks have a data storage life in excess of 30 years.This makes them a better storage medium for dataarchiving as compared to magnetic tapes or magnetic disks.
Ref Page 139 Chapter 8: Secondary Storage Devices Slide 83/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Advantages of Optical Disks
As data once stored on an optical disk becomespermanent, danger of stored data gettinginadvertently erased/overwritten is removed
Due to their compact size and light weight, opticaldisks are easy to handle, store, and port from oneplace to another
Music CDs can be played on a computer having a CD-ROM drive along with a sound board and speakers.This allows computer systems to be also used asmusic systems
Ref Page 139 Chapter 8: Secondary Storage Devices Slide 84/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Limitations of Optical Disks
It is largely read-only (permanent) storage medium.Data once recorded, cannot be erased and hence theoptical disks cannot be reused
The data access speed for optical disks is slower thanmagnetic disks
Optical disks require a complicated drive mechanism
Ref Page 139 Chapter 8: Secondary Storage Devices Slide 85/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Uses of Optical Disks
For distributing large amounts of data at low cost
For distribution of electronic version of conferenceproceedings, journals, magazines, books, productcatalogs, etc
For distribution of new or upgraded versions ofsoftware products by software vendors
(Continued on next slide)
Ref Page 140 Chapter 8: Secondary Storage Devices Slide 86/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Uses of Optical Disks(Continued from previous slide..)
For storage and distribution of a wide variety ofmultimedia applications
For archiving of data, which are not used frequently,but which may be used once in a while
WORM disks are often used by end-user companies tomake permanent storage of their own proprietaryinformation
Ref Page 140 Chapter 8: Secondary Storage Devices Slide 87/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Memory Storage Devices
Flash Drive (Pen Drive)
Relatively new secondary storage device based onflash memory, enabling easy transport of data fromone computer to another
Compact device of the size of a pen, comes invarious shapes and stylish designs and may havedifferent added features
Plug-and-play device that simply plugs into a USB(Universal Serial Bus) port of a computer, treated asremovable drive
Available storage capacities are 8MB, 16MB, 64MB,128MB, 256MB, 512MB, 1GB, 2GB, 4GB, and 8GB
Ref Page 140 Chapter 8: Secondary Storage Devices Slide 88/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Memory Storage Devices
Memory Card (SD/MMC)
Similar to Flash Drive but in card shape
Plug-and-play device that simply plugs into a portof a computer, treated as removable drive
Useful in electronic devices like Camera, musicplayer
Available storage capacities are 8MB, 16MB, 64MB,128MB, 256MB, 512MB, 1GB, 2GB, 4GB, and 8GB
Ref Page 141 Chapter 8: Secondary Storage Devices Slide 89/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Mass Storage Devices
As the name implies, these are storage systemshaving several trillions of bytes of data storagecapacity
They use multiple units of a storage media as a singlesecondary storage device
The three commonly used types are:
1. Disk array, which uses a set of magnetic disks
2. Automated tape library, which uses a set ofmagnetic tapes
3. CD-ROM Jukebox, which uses a set of CD-ROMs
They are relatively slow having average access timesin seconds
Ref Page 142 Chapter 8: Secondary Storage Devices Slide 90/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Disk Array
Set of hard disks and hard disk drives with acontroller mounted in a single box, forming a singlelarge storage unit
It is commonly known as a RAID (Redundant Arrayof Inexpensive Disks)
As a secondary storage device, provides enhancedstorage capacity, enhanced performance, andenhanced reliability
Ref Page 142 Chapter 8: Secondary Storage Devices Slide 91/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Disk Array
Enhanced storage capacity is achieved by usingmultiple disks
Enhanced performance is achieved by using paralleldata transfer technique from multiple disks
Enhanced reliability is achieved by using techniquessuch as mirroring or striping
In mirroring, the system makes exact copies of fileson two hard disks
In striping, a file is partitioned into smaller parts anddifferent parts of the file are stored on different disks
Ref Page 142 Chapter 8: Secondary Storage Devices Slide 92/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
A RAID Unit
Multipledisks
RAID Controller
Computer
Ref Page 142 Chapter 8: Secondary Storage Devices Slide 93/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Automated Tape Library
Set of magnetic tapes and magnetic tape drives witha controller mounted in a single box, forming asingle large storage unit
Large tape library can accommodate up to severalhundred high capacity magnetic tapes bringing thestorage capacity of the storage unit to severalterabytes
Typically used for data archiving and as on-line databackup devices for automated backup in largecomputer centers
Ref Page 142 Chapter 8: Secondary Storage Devices Slide 94/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
CD-ROM Jukebox
Set of CD-ROMs and CD-ROM drives with acontroller mounted in a single box, forming a singlelarge storage unit
Large CD-ROM jukebox can accommodate up toseveral hundred CD-ROM disks bringing the storagecapacity of the storage unit to several terabytes
Used for archiving read-only data in suchapplications as on-line museums, on-line digitallibraries, on-line encyclopedia, etc
Ref Page 143 Chapter 8: Secondary Storage Devices Slide 95/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Storage Hierarchy
As a single type of storage is not superior in speed of access, capacity, andcost, most computer systems make use of a hierarchy of storagetechnologies as shown below.
Smaller capacity, fasteraccess time, and highercost per bit stored
Cachememory
Mainmemory
Larger capacity,slower access time,and lower cost perbit stored
On-line, direct-access andsequential-access secondary
storage device such as hard diskOff-line, direct-access and sequential-accesssecondary storage devices such as magnetictape, floppy disk, zip disk, WORM disk, etc.
Mass storage devices such as tape library, CD juke box, etc.
Ref Page 144 Chapter 8: Secondary Storage Devices Slide 96/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Key Words/Phrases
Automated tape libraryAuxiliary memoryBlockBlockingBlocking factoryCD-ROMCD-ROM jukeboxCheck bitCylinderData transfer rateDirect access deviceDisk arrayDisk controllerDisk driveDisk formattingDisk packDVDEven parityFile Allocation Tube (FAT)
Floppy diskHard diskInter-block gap (IBG)Inter-record gap (IRG)LandLatencyMagnetic diskMagnetic tapeMagnetic tape driveMass storage devicesMaster fileOdd parityOff-line storageOn-line storageOptical diskParallel representationParity bitPit
(Continued on next slide)
Ref Page 144 Chapter 8: Secondary Storage Devices Slide 97/98
Computer Fundamentals: Pradeep K. Sinha & Priti Sinha&
Key Words/Phrases(Continued from previous slide..)
QIC StandardRecordRedundant Array of Inexpensive Disks (RAID)Secondary storageSectorSeek timeSequential access deviceStorage hierarchyTape controllerTrackTransaction fileWinchester diskWORM diskZip disk
Ref Page 144 Chapter 8: Secondary Storage Devices Slide 98/98
top related