Types of Storage Devices

Types of Storage Devices
This lesson includes the following sections:
• Categorizing Storage Devices
• Magnetic Storage Devices
• Optical Storage Devices

Categorizing Storage Devices
Storage devices hold data, even when the computer is turned off.
The physical material that actually holds data is called a storage medium.
The surface of a floppy disk is a storage medium.
The hardware that writes data to or reads data from a storage medium is
called a storage device. A floppy disk drive is a storage device.
The two primary storage technologies are magnetic and optical.

The primary types of magnetic storage are:
• Diskettes (floppy disks)
• Hard disks
• High-capacity floppy disks
• Disk cartridges
• Magnetic tape
The primary 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)
• PhotoCD
Magnetic Storage Devices
• How Magnetic Storage Works
• Formatting
• Disk Areas
• Diskettes
• Hard Disks
• Disk Capacities
• Other Magnetic Storage Devices

-How Magnetic Storage Works ?
A magnetic disk's medium contains iron particles,
which can be polarized—given a magnetic charge—in
one of two directions.
Each particle's direction represents a 1 (on) or 0 (off),
representing each bit of data that the CPU can
recognize.
A disk drive uses read/write heads containing
electromagnets to create magnetic charges on the
medium.
Write head
Random particles
(no data stored)
Medium
Current flow
(write operation)
Organized particles
(represent data)
As the medium
rotates, the head
writes the data.

Magnetic Storage Devices -Formatting
Before a magnetic disk can be used, it must be
formatted—a process that maps the disk's surface and
determines how data will be stored.
During formatting, the drive creates circular tracks
around the disk's surface, then divides each track into
sectors.
The OS organizes sectors into groups, called clusters,
then tracks each file's location according to the clusters
it occupies.
Formatted Disk
Magnetic Storage Devices -Disk Areas
When a disk is formatted, the OS creates four
areas on its surface:
Boot sector – stores the master boot record, a small
program that runs when you first start (boot) the
computer
File allocation table (FAT) – a log that records each
file's location and each sector's status
Root folder – enables the user to store data on the disk
in a logical way
Data area – the portion of the disk that actually holds
data
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.

3.5 inch
floppy
and drive
Magnetic Storage Devices -Hard Disks
Hard disks use multiple platters, stacked on a
spindle. Each platter has two read/write heads, one
for each side.
Hard disks use higher-quality media and a faster
rotational speed than diskettes.
Removable hard disks combine high capacity with
the convenience of diskettes.

Read/write heads
Magnetic Storage Devices -Disk Capacities
Diskettes are available in different capacities, but
the most common store 1.44 MB.
Hard disks store large amounts of data. New PCs
feature hard disks with capacities of 10 GB and
higher.
Magnetic Storage Devices Other
• High-capacity floppy disks offer capacities up to 250
MB and the portability of standard floppy disks.
Disk cartridges are like small removable hard disks,
and can store up to 2 GB.
Magnetic tape systems offer very slow data access,
but provide large capacities and low cost.

Due to long access times, tape
drives are used mainly for backups.

Optical Storage Devices
• How Optical Storage Works
• CD-ROM
• CD-ROM Speeds and Uses
• DVD-ROM
• Other Optical Storage Devices

Optical Storage Devices –
How Optical Storage Works
• An optical disk is a high-capacity storage medium.
An optical drive uses reflected light to read data.
To store data, the disk's metal surface is covered with
tiny dents (pits) and flat spots (lands), which cause
light to be reflected differently.
When an optical drive shines light into a pit, the light
cannot be reflected back. This represents a bit value
of 0 (off). A land reflects light back to its source,
representing a bit value of 1 (on).

1010
CD-ROM
In PCs, the most commonly used
optical storage technology is called
Compact Disk Read-Only Memory (CD-ROM).
• A standard CD-ROM disk can store up to 650
MB of data, or about 70 minutes of audio.
Once data is written to a standard CD-ROM
disk, the data cannot be altered or overwritten.

CD-ROM Speeds and Uses
Early CD-ROM drives were called single speed, and
read data at a rate of 150 KBps. (Hard disks transfer
data at rates of 5 – 15 MBps).
CD-ROM drives now can transfer data at speeds of
up to 7800 KBps. Data transfer speeds are getting
faster.
CD-ROM is typically used to store software
programs. CDs can store audio and video data, as
well as text and program instructions.

Optical Storage Devices -DVD-ROM
A variation of CD-ROM is called Digital Video Disk
Read-Only Memory (DVD-ROM), and is being used
in place of CD-ROM in many newer PCs.
Standard DVD disks store up to 9.4 GB of data—
enough to store an entire movie. Dual-layer DVD
disks can store up to 17 GB.
DVD disks can store so much data because both sides
of the disk are used, along with sophisticated data
compression technologies.
Optical Storage Devices Other
Optical Storage Devices
A CD-Recordable (CD-R) drive lets you record your
own CDs, but data cannot be overwritten once it is
recorded to the disk.
A CD-Rewritable (CD-RW) drive lets you record a
CD, then write new data over the already recorded
data.
PhotoCD technology is used to store digital
photographs.
lesson 9 Review
List four types of magnetic and four types of optical
storage devices.
Identify three common uses for floppy disks.
Name the four areas created on a magnetic disk
during formatting.
Explain how data is stored on the surface of magnetic
and optical disks.
List three variations on optical disk technology.

Types of Storage Devices

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Types of Storage Devices

This lesson includes the following sections:

• Categorizing Storage Devices

• Magnetic Storage Devices

• Optical Storage Devices

The two primary storage technologies are magnetic and optical.

• Diskettes (floppy disks)

• High-capacity floppy disks

• Compact Disk Read-Only Memory (CD-ROM)

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

• How Magnetic Storage Works

• Other Magnetic Storage Devices

-How Magnetic Storage Works ?

A magnetic disk's medium contains iron particles,

which can be polarized—given a magnetic charge—in

one of two directions.

Each particle's direction represents a 1 (on) or 0 (off),

representing each bit of data that the CPU can

A disk drive uses read/write heads containing

electromagnets to create magnetic charges on the

(no data stored)

rotates, the head

writes the data.

Before a magnetic disk can be used, it must be

formatted—a process that maps the disk's surface and

determines how data will be stored.

During formatting, the drive creates circular tracks

around the disk's surface, then divides each track into

The OS organizes sectors into groups, called clusters,

then tracks each file's location according to the clusters

When a disk is formatted, the OS creates four

areas on its surface:

Boot sector – stores the master boot record, a small

program that runs when you first start (boot) the

File allocation table (FAT) – a log that records each

file's location and each sector's status

Root folder – enables the user to store data on the disk

Data area – the portion of the disk that actually holds

Diskette drives, also known as floppy disk drives,

read and write to diskettes (called floppy disks or

Diskettes are used to transfer files between

computers, as a means for distributing software, and

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

Hard disks use multiple platters, stacked on a

spindle. Each platter has two read/write heads, one

for each side.

Hard disks use higher-quality media and a faster

rotational speed than diskettes.

Removable hard disks combine high capacity with

the convenience of diskettes.

Diskettes are available in different capacities, but

the most common store 1.44 MB.

Hard disks store large amounts of data. New PCs

feature hard disks with capacities of 10 GB and

Magnetic Storage Devices

• High-capacity floppy disks offer capacities up to 250

MB and the portability of standard floppy disks.

Disk cartridges are like small removable hard disks,