Lecture 3 Part 2- Storage

7/29/2019 Lecture 3 Part 2- Storage

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INTRODUCTION TO

INFORMATION TECHNOLOGY

StorageLECTURE 3 part 2


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Objectives

Discuss why people and businesses usesecondary storage, not just the computers

main memory, to store information.

Distinguish between the two main types of

magnetic storage, and identify three types of

magnetic disk storage.

Describe two alternatives for extending disk

storage capacity in enterprises.

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Objectives (Continued) Explain why optical storage is of growing

importance in computing and describe the most

commonly used forms of optical storage.



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storage

Storage: The computer process of retaining

information. Storage can be classified into two;

Primary storage

Secondary storage Primary storage: The computer's storage area

for instructions and data currently being used byprograms.

Secondary Storage:A medium (magnetic oroptical) that permanently stores computerinformation for future re-use. This type ofstorage holds data, even when the computer is

turned off. 3/2/2013 Asiimwe Charles 4


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Storage contd

Storage media. The physical components ormaterial on which data is stored. For example; Floppy disk

Hard disk

Zip disks

Compact disk

Storage device. The hardware componentthat writes data to and reads data from astorage media. For example; Floppy disk drive

Hard disk drive

Zip disk drive



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Secondary storage technologies

The two secondary storage technologies aremagnetic and optical.

The types of magnetic storage are;

Diskettes (floppy disks)

Hard disks

High-capacity floppy disks

Magnetic tape

etc



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Secondary storage technologies

The types of optical storage are; Compact Disk Read-Only Memory

(CD-ROM)

Digital Video Disk Read-Only Memory

(DVD-ROM)

CD-Recordable (CD-R)

CD-Rewritable (CD-RW)

etc



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Storage contd

The primary types of optical storage are asfollows;

Compact Disk Read-Only Memory (CD-ROM)

Digital Video Disk Read-Only Memory (DVD-ROM)

CD-Recordable (CD-R)

CD-Re-Writable (CD-RW)



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Magnetic Storage devices

The purpose of storage devices is to holddata even when the computer is turned off

so that the data can be used whenever it is

needed.

Storage involves the processes of writingdata to the storage medium and reading data

from the storage medium.

Writing data means recording data on the

surface of the disk where it is stored for later

use.

Reading data means retrieving data from the

disks surface for later use.3/2/2013 Asiimwe Charles 9


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Magnetic storage devices

Because they all use the same medium (the

material on which data is stored), diskette

drives, hard disk drives, and tape drives use

similar technique for writing and reading data.

The question is; how do magnetic storagedevices work?



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How magnetic storage works

The surface of disks and magnetic tapes are

coated with millions of tiny iron particles so

that data can be stored on them.

Each of these particles can act as a magnet

taking on the magnetic field when subjected toelectromagnet (Magnetic force that isgenerated by electricity).

The read/write heads of a hard disk drive,

floppy drive, or tape drive contain

electromagnets, which generate magnetic

fields in the iron particles on the storage

medium as the head passes over the disk orta e. 3/2/2013 Asiimwe Charles 11


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How magnetic storage works

As the read/write head passes on the surface

of the disk or tape, each iron particle is

arranged in a direction representing a 1 (on)

or 0 (off), representing each bit of data that

the CPU can recognize.

See illustration diagrams on the next slide..



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Random particles

(no data stored)Current flow

(write operation)

Organized particles

(represent data)

Medium

Write head

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As the medium

rotates, the head

writes the data.



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Magnetic Storage Devices -

Diskettes Diskette drives, also known as floppy disk drives,

read and write to diskettes (called floppy disks or

floppies).

Diskettes are used to transfer files between

computers, as a means for distributing software,

and as a backup medium.

Diskettes come in two sizes: 5.25-inch and 3.5-

inch



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3.5 inch

floppy

and drive



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Diskette (Floppy disk)

The figure on the previous slide shows adiskette and a diskette drive.

The drive includes a motorthat rotates the

disk on a spindle and read/write heads that

can move to any spot on the disks surface asthe disk spins.

This capability is important because it allows

the heads to access data randomly rather

than sequentially.

In other words, the heads can skip from one

spot to another without having to scan through

all the data in between.3/2/2013 Asiimwe Charles 17


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Three most common uses of

diskettes

Moving files between computers that are notconnected through network. Data can be

copied to a diskette, remove the diskette from

the first computers hard drive, and insert in in

another computers drive. Loading new programs onto a system.

Backing up Data or Programs. Backing up is

the process of creating a duplicate set of

programs and/data for safe keeping. Diskettes

have small storage capacity so they are often

used to back up small data files other than

programs. 3/2/2013 Asiimwe Charles 18


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Types of Diskettes

During the 1980s, most PCs used 5.25 inch

diskettes. Today, the 3.5 inch diskettes have

completely replaced its 5.25 inch diskette.

In fact, you will encounter 5.25-inch disks only

when using older computer systems. New systems use the smaller diskette almost

exclusively, unless a 5.25 inch disk drive has

been added.



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5.25 inch floppy disk



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3.5 Inch floppy disk



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Hard disk


Hard disk: A form of secondary

storage that stores data on plattersdivided into circular tracks and

sectors, which can be read by a

read/write head that spins around

the rotating disks.


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Hard disk platter



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Hard disk

Track: The area in which data andinformation are stored on a disk.

Sector: A subdivision of a track on a

magnetic disk; used to improve access todata or information.



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Hard disk & floppy disk compared

Unlike diskettes, where the disk and drive are

separate, the hard disk and drive are a singleunit. It includes the hard disk, the motor that

spins the platters, and a set of read/write

heads.

Hard disks have become the most common

storage device because they are convenient

and cost effective. In both speed and capacity,

they out perform diskettes.A high density 3.5-inch diskette can store

1.44MB of data. Hard disks in contrast, offer

capacities from about several hundred

megabytes to Gigabytes, Terabytes and more.3/2/2013 Asiimwe Charles 25


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Hard disk contd

Hard disks also hold more data because theyusually include multiple platters, stacked on

top of one another on a spindle. Each platter

has two read/write heads, one for each side

except for the bottom side of the bottomplatter.



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Hard disk



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Hard disk head crash

Hard disks have one major draw back; to

achieve optimum performance, the read/write

head must be extremely close to the surface of

the disk without actually touching it.

In fact, the read/write heads fly so closely tothe surface of the disk that if human hair, dust

particle, or even a finger print were placed on

the disk, it would bridge the gap between the

head and the disk and cause the head tocrash.

A head crash in which the head touches thedisk, can destroy the data stored in the area of

the crash. 3/2/2013 Asiimwe Charles 28


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Hard disk



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Storage

Hard Disk (Continued)

Disk Controller Interfaces

Hard Disk Controller: A hardware interface that may be

built into the hard drive itself, in the form of an

expansion board, or a connection on the system

board.

Hard disks access types:

ATA (IDE, EIDE)

Serial ATA (SATA) SCSI

External access types:

IEEE 1394/FireWire

USB 3/2/2013 Asiimwe Charles 30


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Storage

Hard Disk (Continued)

Disk Controller Interfaces Integrated Drive Electronics (IDE): A standard electronic

interface used between the bus or data path on a

computer system board and the computers disk

storage devices.

SATA (Serial Advanced Technology Attachment) offers

advantages over the older IDE interface: primarily faster

data transfer, the ability to remove or add devices while

operating (hot swapping), thinner cables that let air-cooling work more efficiently, and more reliable

operation

Small Computer System Interface (SCSI): A device3/2/2013 Asiimwe Charles 31


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Storage

Hard Disk

Disk Controller Interfaces Universal Service Bus (USB): A recent addition to

PCs that can connect up to 128 devices, rangingfrom computer disk storage to a variety of

multimedia devices.

Fire Wire: One of the fastest peripheral interfacestandards ever developed.

Disk Cache:Disk caching allows the system to storeinformation that is frequently read from a disk in RAM.



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Optical storage

Refers to storage systems that use lightbeams to read data from the surface of optical

disk.

Since the mid 1990s, nearly all new PCs have

been sold with a built-in CD-ROM drive. However, consumers are buying more and

more systems with DVD-ROM drives rather

than the standard CD-ROM units.

These devices fall into the category of optical

storage because they store data on a

reflective surface so it can be read by a beam

of light. 3/2/2013 Asiimwe Charles 33


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How the CD ROM drive reads data

The CD ROM drive for music or data reads 0sand 1s from a spinning disk by focusing a

laser on the disk surface.

Some of the areas of the disk surface reflect

the laser beam into the sensor, and otherareas scatter the beam of light.

A spot that reflects the laser beam into the

sensor is interpreted as 1, and the absence of

a reflection is interpreted as 0.

Data is stored in form oflands which are flatareas on a disk surface and pits which are

depressions or hollows.3/2/2013 Asiimwe Charles 34


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CDs contd

A land reflects the laser light into the sensor

(indicating a data bit 1), and a pit scatters thelight (indicating a data bit of 0). (see next

slide for illustration)

A standard compact disk can store between650MB and 700MB of data.



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1 0



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Optical storage technologies

CD-ROM. Short for compact disk-read onlymemory, When u buy such a CD from the

shop, you can only read from it but you cannot

save anything on it.

CD-R. Short for Compact Disk Recordable whichallows users to write data on this disk and once it

has been written, that data cannot be changed (or

over written). CD-R disks can be read by CD-ROM

drive.

CD-RW. Short for Compact Disk Re-Writable which

allows users to write data on a disk, and this data

can be over-written, meaning that the data can be

updated after it has been placed on the disk. CD-3/2/2013 Asiimwe Charles 37


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Optical storage technologies contd

DVD. Short for Digital Video Disk or DigitalVersatile Disk.

This is a high density optical medium capable

of storing a full-length movie on a single disk

the size of a standard compact disk (CD).

Unlike a standard CD, which stores data on

only one side, a DVD-format disk stores data

on both sides by use of compressiontechnologies.

Newer DVDs can store several gigabytes of

data.

A DVD drive has the ca abilit of readin a3/2/2013 Asiimwe Charles 38


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Optical storage technologies

Blu-Ray: A medium designed to supersedethe standard DVD format.

Its main purpose is to store high-definition

video and other types of data with up to 25GB

per single layer and up to 50 GB per duallayered disk.

The disk has the same physical dimensions

as standard DVDs and CDs.

It has a major advantage of huge storage

capacity, more clear than a DVD and can play

in DVD player.

Its major disadvantage is that its very3/2/2013 Asiimwe Charles 39


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Optical Media Are Susceptible to

Damage..

Unlike hard disks, which are in a sealed unit,and floppy disks, which are in a protective

housing, optical discs have no protection once

they are removed from their storage case.

Optical discs are vulnerable to scratches, dirt,

breakage and fingerprints, although

fingerprints can usually be removed by wiping

with a soft, damp cloth. Therefore, do not touch the surface of optical

discs, hold them by the outer edges and the

hole in the middle.

Documents

Lecture 3 Part 2- Storage