Introduction to Computers
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Introduction to Computers

Storage devices and storage media. Storage devices are designed for long-term, non-volatile retention of electronic data. A . storage medium. is a disk, tape, CD, DVD or other recording surface that retains data.

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Introduction to Computers

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Introduction to Computers


Storage devices and storage media

Storage devices are designed for long-term, non-volatile retention of electronic data


storage medium

is a disk, tape, CD, DVD or other recording surface that retains data


storage device

records and reads the data on the storage medium

Hard disk and flash memory combine the medium and device into one unit

CD, DVD, & tape allow the media to be removed from the device


Types of storage

Magnetic storage

Includes hard disk and magnetic tape

Magnetizes tiny particles on the recording surface

Optical storage

Includes CDs and DVDs

Stores data as tiny light spots (lands) or dark spots (pits) on the disk surface

Flash memory

A non-volatile form of solid state memory circuitry


Magnetic storage

Magnetic storage device has a read/write head

Data written by magnetizing particles on a surface

Magnetization can later be read and deciphered

Susceptible to dust, smoke, heat, but especially magnetic or strong electrical fields

Don’t put a powerful speaker near magnetic media

Speakers contain magnets that erase the media

Magnetic media tends to degrade over time

But this process takes years


Optical storage

A laser is directed at the surface of the disk

The pattern of dark and light spots is reflected back

The pattern of reflected light is read as data

CDs and DVDs much less sensitive to damage

Fairly insensitive to dust, smoke, heat

Not magnetic so not harmed by electrical fields

Does not degrade over time

Generally more reliable than magnetic media

But slower access time and more difficult to write to


Flash memory

Functions similar to random access memory

But uses an entirely different type of technology

Non-volatile, power not needed to maintain data

Fast read times but not as fast as RAM

Completely electronic, no moving parts

Thus highly reliable and very durable

Not sensitive to dust, smoke, magnetic fields

Both solid state drives (SSD’s) and flash drives are based on this type of storage technology


Drive bays hold storage devices

PCs have

drive bays

to hold

storage devices

Two sizes of drive bays

5 ¼ inch drive bay

3 ½ inch drive bay

Laptops may also have their

own version of a drive bay


Evaluating types of storage

Use the following factors when evaluating the relative merits of different types of storage

Storage capacity - hard disk & tape have the largest capacity by far, SSD’s come in a close second

Access speed – SSD & hard disk are fastest by far

Durability – SSD, hard disk, CD, DVD all very good

Portability – CD, DVD, flash memory most portable


Hard disk positives

Still the main storage device in most computers

Huge storage capacity, 500 to 2000 GB & more

Fast access to data

Extremely low cost per megabyte

Avoids magnetic storage durability issues by operating in a closed environment

Manufactured in clean rooms

Disk surface permanently enclosed

If you remove the cover, you’ll never use it again


Hard disk design

Often has multiple platters

2 read/write heads for each platter, one for the top and one for the bottom

Platters spin at a high rate of speed, 5400-7200 rpm

Read/write head moves across the surface to read data anywhere on surface


Hard disk negatives

Hard disks are highly reliable but susceptible to:

A head crash can damage data on the disk

Can occur when dust or other contaminant gets between the read/write head and disk surface

Can also occur from jarring hard disk while in use

Never move a desktop computer while in use

Read/write head retracts from disk when turned off

Laptops have shock-mounted hard drives

Mechanical failure – any machine can break


SSD’s slowly replacing hard disks

SSD is an acronym for

solid state drive

Calling an SSD a “drive” is a misnomer since it is completely electronic with no moving parts

Based on flash memory technology but far faster

Uses hard drive data pathway instead of a USB port

More reliable, durable, & faster than hard drives

The only downside to SSD’s is cost

Less capacity at a significantly higher cost

Hard disks still have a cost per megabyte advantage


removable and external hard disks

Removable hard drives

Transforms a drive bay into a “drawer”

Can slide a removable hard drive into the “drawer”

Can easily remove and replace it with another drive

External hard drives are designed to be used outside the system unit

Connect to the computer through the USB port

USB port limitations cause access time to be slower

External and removable drives can be terrific as backup devices to save a copy of your hard disk


USB Flash Memory Devices

Portable device often called flash drive, jump drive, thumb drive, memory key, & other names

As with SSD’s the term “drive” is a misnomer since it’s completely electronic with no moving parts

External device that uses flash memory technology

Small, easy to carry, and plugs into any USB port

Best means to transport data from place to place

Reliable & durable but not indestructible

Can be hard to keep track of and easily lost

Most store from 8 GB to 128 GB of data


CD storage Positives

CDs are extremely durable

Very inexpensive to manufacture and purchase

Ideal for distributing software or other large files

Access speed much slower than flash memory

Can create your own CDs with CD-R or CD-RW

Great for archiving large files such as photos

Good storage capacity, up to 700 MB

A CD drive is a necessity, even if an external one


CD storage negatives

Access speed much slower than a hard disk

Storage capacity less than flash memory and far less than hard disk


Writing data to your CD

CD-ROM stands for Compact Disk - Read Only

Can’t write data to a CD-ROM

Can buy CD-R disks, Compact Disk-Recordable

Allows you to create your own CDs

Can write only once but read as much as you like

CD-RW stands for Compact Disk Rewritable

Also allows you to create your own CDs

Can write and read as often as you like

Must have a CD-R or CD-RW drive to do this

Most CD drives work with both CD-R and CD-RW


CD-R versus CD-RW

CD-R disks are much cheaper than CD-RW

So think carefully when buying

Do you really need the “rewritable” capability?

For example, if archiving photos it’s usually more cost effective to use CD-R

It’s unlikely you’ll make further changes to that disk

If the data on a CD-R becomes out of date….

Can still use it as a coaster… or a


CD-RWs don’t get out of date, just rewrite them


DVD storage

Similar positives to CDs

Durable and very inexpensive to manufacture

Far better storage capacity, 4.7 GB versus 700 MB

Only negative is a slower access speed similar to CD access speeds

Must have a DVD drive to read a DVD

Most optical drives (but not all) sold today are combo drives that read both CDs and DVDs

A DVD drive is a necessity, even if external


CD and DVD access speeds

CD and DVD speed is expressed in an odd way

Both are expressed in terms of how many times faster than the 1st model of CD or DVD drive

DVD Drive Speed Data Transfer Rate CD Drive Speed

1X 11.08 Mbps 9X

2X 22.16 Mbps 18X

3X 44.32 Mbps 36X

4X 55.40 Mbps 46X


Does anyone still use tape?

Magnetic tape was a popular form of general use storage in the 1960s

Tape is no longer a primary storage device

Inconvenient and slow, can only read sequentially

Tape now used primarily as a backup device

High storage capacity, comparable to hard disks

Heavily used by businesses for data backup

Tape drives are available in both internal and external models