tuesday 19 th october, 2015 information technology
TRANSCRIPT
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 Becoming outdated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.