Tuesday 19th October, 2015

Information Technology

Secondary Storage

At the end of this lesson you will be able to:

Categorize the different types of secondary

storage media

Explain how information is accessed from

different types of secondary storage media

Identify portability and significance

Secondary Storage

At the end of this lesson you will be able to:

Select secondary storage media in terms of

speed

Select secondary storage media in terms of

capacity

Choose which secondary storage media are

suited for our everyday needs.

Secondary Storage

Secondary Storage

Magnetic Media/ Devices

Secondary Storage

https://www.youtube.com/watch?v=f3BNHhfTsvk

Magnetism Video (2.20)

Secondary Storage

Magnetic Tape

Secondary Storage

Magnetic Tape –

A secondary storage

medium in which data are stored by means of

magnetised and unmagnetised spots on tape;

can store information only sequentially or

serially.

Secondary Storage

Storage of Data on Magnetic Tape

G

A

P

Record Record Record

G

A

P

Record Record Record

G

A

P

Block Block

Separates Blocks of Data

Secondary Storage

Advantages –

1. It is low in cost

2. Relatively stable storage medium

3. Reusable meaning its contents can be erased in

order to store new information

4. Capacity – Can store between 200MB to 10 GB

5. Often used as backup e.g. school network

Secondary Storage

Disadvantages –

1. It stores information sequentially or serially which

causes it to be slow

2. Records cannot be updated in place (‘in situ’).

3. Tape must be stored in a suitable environment (tape

can age and crack over time and storage

environment must be controlled i.e. tapes placed

upright, cool and low humidity)

Secondary Storage

Floppy Disc –

A flexible, inexpensive

magnetic disc used as secondary storage

medium; primarily used with PCs.

Secondary Storage

Floppy Discs

Secondary Storage

Storage of Data on Floppy Disc

Sector

Track

Data Records

Inter-sector Gap

Secondary Storage

Advantages –

1. They are very cheap

2. Small, lightweight and convenient

3. Exchangeable

Secondary Storage

Disadvantages –

1. Floppies are vulnerable – short shelf life,

susceptible to dirt and dust

2. Time consuming if access is needed to view many

files over short period of time

3. Low storage capacity, 1.44 MB

4. Becoming outdated

Secondary StorageHard Disc Drive, HDD –

Magnetic hard disks are thin

metallic platters with an iron oxide coating.

Several discs may be mounted together on a

vertical shaft where they rotate at speeds

approx. 3,500 to 7,200 rpm.

Secondary Storage

Hard Disc Drive, HDD

Secondary Storage

HDD Schematic

Secondary Storage

Advantages –

1. Individual records can be accessed directly,

within milliseconds e.g. in an airline reservation

system or customer information systems

2. Very high capacity, at low cost (per character

stored). Can start from 120GB upwards.

Secondary Storage

Advantages –

4. Disc packs are convenient to handle and store

5. Disc storage permits records and pieces of related data to be organised and combined easily

6. Vacuum packaged

Secondary Storage

Disadvantages –

1. Hard Discs are more expensive than most

secondary storage devices viz. tapes, floppy

discs, CDs and DVDs.

2. Susceptible to dust, static electricity, head

crashes

3. Backup is required.

Secondary Storage

Optical Media/ Devices

Secondary Storage

CDs and DVDs

https://www.youtube.com/watch?v=uwYcnLDApsQ

Secondary StorageOptical Disc –

A disc on which data are recorded and

read by laser beams rather than by magnetic means.

The laser burn microscopic pits in a spiral track when

writing in which a pit can be a “0” while a clear area a

“1”. Such discs can store data from 700 MB as in CDs

to 4.7 GB as in DVDs.

Secondary Storage

Cross-section of an Optical Disc

Secondary Storage

Operation of an Optical Disc

Secondary Storage

Compact Disc, CD –

An optical disc system

used with PCs. Massive quantities of data

can be stored in a highly compact form e.g.

data, music and videos.

Available in CD-ROM/R/RW

Secondary Storage

Compact Discs

Secondary Storage

Digital Video Disc, DVD –

Another optical disc

of even higher capacity, with the ability to store

data starting from 4.7 GB, enough to store a

full-length movie.

Available in DVD+R, DVD+RW, DVD-R, DVD-

RW and DVD-ROM.

Secondary StorageAdvantages –

1. They have massive storage capacities

2. High-quality pictures and sounds can be

achieved without noticeable deterioration, even

after continuous use

3. Information can be retrieved quickly by direct

access

Secondary Storage

Advantages –

5. Discs are coated against dust and most

scratches

6. Relatively cheap and easy to access

7. Reliable.

Secondary Storage

Disadvantages –

1. Data tends to become corrupted on certain

types of discs

2. Not all writeable software supports

standards for writing

Secondary Storage

Solid State Media/ Devices

Secondary Storage

Solid-state device-

Electronic device in which electricity flows through solid semiconductor crystals or contains a EEPROM chip

Secondary Storage

Secondary StorageFlash Drive –

A small, portable flash memory card that plugs

into a computers. USB port and functions as a

portable hard drive. USB flash drives are touted

as being easy-to-use as they are small enough

to be carried in a pocket and can plug into any

computer with a USB drive.

Secondary Storage

Flash Drive cont’d –

USB flash drives have less

storage capacity than an external hard drive,

but they are smaller and more durable

because they do not contain any internal

moving parts.

Secondary Storage

Secondary Storage

Flash Memory –

Flash memory is used for easy

and fast information storage in computers,

digital cameras and home video game

consoles. It is used more like a hard drive

than as RAM.

Secondary Storage

Flash Memory cont’d –

In fact, flash memory is known as

a solid state storage device, meaning there

are no moving parts -- everything is electronic

instead of mechanical.

Secondary Storage

Secondary Storage

Secondary StorageSolid State Drive, SSD –

A traditional hard disk drive (HDD) consists

of a spinning disk with a read/write head on a

mechanical arm. An SSD, on the other hand, has

an array of semiconductor memory organized as

a disk drive, using integrated circuits (ICs) rather

than magnetic or optical storage media.

Secondary Storage

Recap –

Categorize the different types of secondary storage media

Explain how information is accessed from different types

of secondary storage media

Identify portability and significance

Secondary StorageRecap –

Select secondary storage media in terms of speed

Select secondary storage media in terms of capacity

Choose which secondary storage media are suited for

our everyday needs.

Secondary Storage

Thank you for being a great class and have a good afternoon!

Please check google drive for today’s lesson.