7.
1 Secondary Storage Devices
Secondary Storage Device
Stores data, operating system and
application software on a computer system
Also called backing storage
Non-volatile
7.1 Secondary Storage Devices
Secondary Storage Device
Reading data from secondary storage
device
Secondary 1. Issue a read CPU
storage instruction
device
2. Load data 3. Load data and
into main continue
memory execution
Main memory
7.1 Secondary Storage Devices
Secondary Storage Device
Writing data into secondary storage device
Secondary 2. Issue a write CPU
storage instruction
device
3. Write data 1. Store data into
into main memory
secondary
storage Main memory
7.1 Secondary Storage Devices
The Speed of a Secondary Storage
Device
Access
Access time
time Data
Data transfer
transfer
rate
rate
•• The
The average
average time
time •• The
The amount
amount of of data
data
taken
taken for
for the
the device
device that
that can
can bebe
to
to search
search andand read
read transferred
transferred between
between
the
the required
required data
data onon the
the main
main memory
memory
the
the storage
storage medium
medium and
and aa storage
storage device
device
•• Shorter
Shorter access
access time
time per
per second
second
means
means higher
higher •• Unit:
Unit: bps
bps oror Bps
Bps
searching
searching speed
speed •• Higher
Higher rate
rate means
means
faster
faster
reading/writing
reading/writing
process
process
7.1 Secondary Storage Devices
Storage Capacity
The maximum amount of data that can be
stored on a storage medium.
Measured in kilobyte, megabyte, gigabyte
or terabyte
Unit Abbreviation Value
Kilobyte KB 1 KB = 210 B = 1,024 B
Megabyte MB 1 MB = 220 B = 1,024 KB
Gigabyte GB 1 GB = 230 B = 1,024 MB
Terabyte TB 1 TB = 240 B = 1,024 GB
7.1 Secondary Storage Devices
Magnetic and Optical Storage
Devices
Magnetic
Magnetic Storage
Storage Optical
Optical Storage
Storage
Devices
Devices Devices
Devices
•• Example:
Example: floppy
floppy •• Example:
Example: CD-ROM,
CD-ROM,
disks,
disks, hard
hard disks
disks DVD
DVD
•• Data
Data stored
stored as as •• Data
Data stored
stored as
as
electromagnetic
electromagnetic microscopic
microscopic light
light and
and
charges
charges on on magnetic
magnetic dark
dark spots
spots on
on the
the
surfaces
surfaces of of the
the disk
disk surface.
surface.
storage
storage units.
units. •• Less
Less susceptible
susceptible to
to
•• Gradual
Gradual loss
loss of
of environmental
environmental
magnetic
magnetic charges
charges damage
damage
leads
leads to
to loss
loss ofof data
data
7.1 Secondary Storage Devices
Magnetic and Optical Storage
Devices
Magnetic
Magnetic Storage
Storage Optical
Optical Storage
Storage
Devices
Devices Devices
Devices
•• Example:
Example: floppy
floppy •• Example:
Example: CD-ROM,
CD-ROM,
disks,
disks, hard
hard disks
disks DVD
DVD
•• Data
Data stored
stored as as •• Data
Data stored
stored as
as
electromagnetic
electromagnetic microscopic
microscopic light
light and
and
charges
charges on on magnetic
magnetic dark
dark spots
spots on
on the
the
surfaces
surfaces of of the
the disk
disk surface.
surface.
storage
storage units.
units. •• Less
Less susceptible
susceptible to
to
•• Gradual
Gradual loss
loss of
of environmental
environmental
magnetic
magnetic charges
charges damage
damage
leads
leads to
to loss
loss ofof data
data
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Floppy Disk
Protective
plastic
casing
Circular
flexible
plastic disk
with
magnetic
coating
3.5 inch
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Floppy Disk
Stores data in tracks and sectors
Two
Sector recordable
• A small arc surfaces
• Can store
up to 512 Track
bytes of • A circular
data band
80 tracks
Storage capacity
= (2 x 80 x 18 x 512) 18 sectors
= 1,474,560 bytes
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Floppy disk
Access data on a floppy disk
Its read/write head transfers data
between the computer and the disk
A floppy disk drive
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Floppy Disk
Features
Handy, cheap and rewritable
Usage
Back up files
Transfer a small amount of data between
computers
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Hard Disk
Consists of platters, which store data
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Data access of hard disk
Direct access
The access arm moves the read/write
head on the platters.
The drive then rotates the platters to the
proper position. Sector
Cluster
Track Read/write head
Platter
Access arm
Cylinder
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Hard Disk
Factors determining the performance
Seek
Seek Time
Time Drive
Drive Rotational
Rotational
•• Time
Time taken
taken toto move
move Speed
Speed
the
the read/write
read/write head
head •• The
The number
number of of
over
over the
the right
right track
track and
and revolutions
revolutions the
the disk
disk
sector
sector platters
platters make
make perper
•• Higher
Higher speed
speed rotations
rotations minutes
minutes
of
of disk
disk plates
plates and
and •• Unit:
Unit: revolution
revolution per
per
faster
faster movement
movement of of minute
minute (rpm)
(rpm)
read/write
read/write head
head leads
leads •• Higher
Higher rotational
rotational
to
to shorter
shorter seek
seek time
time speed
speed leads
leads to
to higher
higher
data
data transfer
transfer rate
rate
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Magnetic tapes
Consist of a magnetically coated strip of
plastic on which data is stored
Magnetically
coated
plastic strip
7.2 Types of Secondary Storage
Devices
Magnetic Storage Devices
Magnetic tapes
Require sequential access
Tape drive has to move through all
preceding data before it can access
the desired data.
Relatively slow storage but large storage
capacity at low cost
Suitable for long-term storage and
backup
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Compact Disk Read-Only Memory (CD-ROM)
A round disk coated with a metallic
surface
Data can be stored and accessed via
laser technology.
Content is set
permanently
when
manufactured.
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Compact Disk Read-Only Memory (CD-ROM)
CD-ROM drive
The device that reads data from a
CD-ROM
Performance mainly measured by its
data transfer rate
A N× CD-ROM
drive can
transfer N × 150
KB per second
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Compact Disk Read-Only Memory (CD-ROM)
CD-ROM drive focuses a laser beam on
the layer so as to read the stored data
Lens Lens
Pit No Land Reflected
reflection beam
Light-sensing Light-sensing
diode diode
“0” “1”
Laser diode Laser diode
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Compact Disk Read-Only Memory (CD-ROM)
Variations of CD-ROM
Compact disk-recordable (CD-R)
Compact disk-rewritable (CD-RW)
Can read data Can write data Can modify
Drive
from onto data of
CD-ROM CD-ROM, CD-R,
- -
drive CD-RW
CD-R CD-ROM, CD-R,
CD-R -
drive CD-RW
CD-RW CD-ROM, CD-R,
CD-R, CD-RW CD-RW
drive CD-RW
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Digital Versatile Disk (DVD)
Looks like CD-ROM
Can store up to 17 GB of data
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Digital Versatile Disk (DVD)
DVD drive
Reads data from DVD and CD-ROM
A N× drive transfers N × 1.32 MB data
per second
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Digital Versatile Disk (DVD)
Variations
DVD+R and DVD-R
Write-once optical disks
DVD+RW and DVD-RW
Rewritable versions of DVD+R and
DVD-R respectively
DVD-RAM
Allows users to copy, modify and delete
files
7.2 Types of Secondary Storage
Devices
Optical Storage Devices
Digital Versatile Disk (DVD)
Features
Large capacity
Medium speed
Low unit cost
DVD+R and DVD-R: not rewritable
DVD+RW and DVD-R: rewritable
Usage
Back up files
Movie and multimedia file distribution
7.2 Types of Secondary Storage
Devices
Other Forms of Secondary Storage
Devices
Magneto-Optical (MO) Disks
Combine magnetic and optical methods
to read and write data
Can store up to 9.1 GB of data
7.2 Types of Secondary Storage
Devices
Other Forms of Secondary Storage
Devices
Magneto-Optical (MO) Disks
Features
Medium capacity
Medium speed
High unit cost
Rewritable
Reliable long-term storage
Usage
Back up files
7.2 Types of Secondary Storage
Devices
Other Forms of Secondary Storage
Devices
Memory Card
Small memory chips on cards
Store data in electronic format
Extend storage capacity of
Notebook computers
PDAs
MP3 players
Digital cameras
7.2 Types of Secondary Storage
Devices
Other Forms of Secondary Storage
Devices
Memory Card
Types
Compact flash
Multimedia card
Memory stick
7.2 Types of Secondary Storage
Devices
Other Forms of Secondary Storage
Devices
Memory Card
Memory Card Reader
Provides a data transfer between a
memory card and a computer
Compact flash All-in-one
reader card reader
7.2 Types of Secondary Storage
Devices
Other Forms of Secondary Storage
Devices
Memory Card
Features
Wide range of capacities available
Medium speed
High unit cost
Rewritable
Small, light, portable
Quiet in operation
Less susceptible to environmental
change
7.2 Types of Secondary Storage
Devices
Other Forms of Secondary Storage
Devices
Memory Card
Features
Wide range of capacities available
Medium speed
High unit cost
Rewritable
Small, light, portable
Quiet in operation
Less susceptible to environmental
change
7.3 Interface Cards
Interface Card
A circuit board that can be slotted into the
motherboard
Expands the capability of the system
Video/graphic card Sound card
Computer Video Digital Audio
outputs signals data signals
7.3 Interface Cards
Interface Card
Network
Modem card
interface card
Transmit data over a Transmit data over a
telephone line cable
7.3 Interface Cards
Interface Card
Network
Modem card
interface card
Transmit data over a Transmit data over a
telephone line cable
