Discovering Computers
Chapter 7
Storage
Ch 1 – Introduction
Ch 2 – Internet & WWW
Ch 3 – Application Software
Ch 4
Processor
Control
Control
Unit
Unit
Arithmetic
Arithmetic
Logic
(ALU)
Logic Unit
Unit (ALU)
Instructions
Data
Information
MemoryInformation Output
Input
Data
Devices Instructions
Devices
Instructions
Ch 5
Ch 6
Data
Information
Storage Devices
Ch 8 – System Software
Ch 7
2
3
What a storage device does?
Hardware that
Reading
Transfers
items from storage
media to memory
writes
records to the medium
holds
them and
reads from
Writing
Transfers
items from memory
to storage media
4
Reading is the
process of
transferring items
from a storage
medium into memory
Writing is the
process of
transferring items
from memory to a
storage medium
5
6
Storage device and a storage medium
storage device
Hardware that
records, holds and
retrieves items to
and from a storage
medium
storage
medium
Physical material
on which a
computer keeps
info
7
How does storage differ from memory?
Stores items for
future use,
rather than
current use
Stores for a
long time,
rather than
temporarily
Storage is
nonvolatile,
rather than
volatile
To work
with a file,
you read a
part (a
block of
records)
from
storage
(block by
block) and
place it in
memory
When you are
finished with
the block of a
file, you write
it from
memory to the
storage
8
How does volatility compare?
Contents
of storage
retained
when
power is
off nonvolatile
Screen display and contents of
RAM are volatile –
erased when power is off
9
What is capacity? Number
of bytes storage
medium can hold
Storage Term
Abbreviation
Number of bytes
Kilobyte
KB
1 thousand
Megabyte
MB
1 million
Gigabyte
GB
1 billion
Terabyte
TB
1 trillion
Petabyte
PB
1 quadrillion
Google believes that the
“plummeting price of storage” will allow
iPods of the future (2020 A.D. ) to hold “any
video ever produced”.
11
Access time:
 The amount of
time it takes a
storage device
to locate an
item on a
storage
medium
12
13
What is access time?
Amount of time
it takes
device to
locate block
on disk –
measured in
millisec /
microsec /
nanosec /
picosec
Memory
(RAM)
cost
Hard
Disk
Flash
memory
Compact disk
Tape
speed
What is transfer rate?
Time required to deliver a block from storage to memory
in kilobytes/sec (KB/sec) or megabytes/sec (MB/sec)
Primary Storage
Memory (most RAM)
Items waiting to be interpreted
and executed by the processor
faster
transfer Secondary Storage
rates
Hard Disk
Flash Memory Cards
and USB Flash Drives
slower
transfer
rates
CDs and DVDs
Tape
Floppy Disk
Operating system, application
software, user data and information
Digital pictures or files
to be transported
Software, backups, movies, music
Backups
Small files to be transported
14
Hard disk contains one or
more inflexible, circular
platters that use magnetic
particles to store data,
instructions, and information
15
16
Characteristics of a hard disk:
Capacity
Platters
Read/Write
Heads
Cylinders
Sectors and
Tracks
Revolutions
per Minute
Transfer
Rate
Access
Time
17
Sample: Hard Disk Characteristics
Advertised capacity
500 GB
Platters
4
Read/write heads 8
Cylinders
16,383
Bytes per sector 512
Sectors per track 63
Sectors per drive 973,773,168
Revolutions per minute 7,200
Transfer rate
300 MB per second
Access time
8.5 ms
18
19
Calculating capacity of a hard drive
Sector stores
512 bytes of
data
16383 cylinders times 8 tracks in a cylinder times
63 sectors per track times 512 bytes per sector
= 500 GB
20
21
An external hard disk is a separate
free-standing hard disk that connects
to your computer with a cable or
wirelessly
A removable hard disk is a hard
disk that you insert and remove from
a drive
Internal and external hard disks are
available in miniature sizes
(miniature hard disks)
22
23
Arm Head
Platter
Sector
Track
Cylinder
Hard Disk Terminology
Track
platter
track
sector
read/write
head
platter
sides
24
cylinder
25
26
Track is the narrow
recording band that
forms full circle on
disk surface
Cylinder is the collection
of single tracks
through all platters
Single movement of
read/write head arms
can read any track on
the cylinder
cylinder
track
What is a head crash?
 Occurs when read/write head touches platter surface
 Spinning creates cushion of air that floats read/write head
above platter

A smoke particle, dust particle, or human hair could render drive
unusable
27
28
How does RAID work?
Redundant Array of Independent Disks
Disk system that duplicates data, instructions, and information to
improve data reliability

Mirroring has one backup disk for each primary disk
mirroring
(RAID Level 1)
External hard disk—freestanding Removable hard disk—
hard disk that connects to system unit you insert and remove
from hard disk drive
29
What is a disk cache?
 Portion of memory
that processor uses
to store frequently
accessed items
first request
for data goes to disk
cache
second request
for data goes to hard
disk
30
31
Disk History
1973:
1979:
140 MB
2,300 Mbytes = 2.3 GB
32
1 inch disk drive!

Hitachi 2007 release
• Development driven by
iPods & digital cameras
• 20GB, 5-10MB/s
Flash Memory Storage
Flash memory chips contain no moving parts –
solid state drives; they have several
advantages over magnetic hard disks:
Faster access
time
Faster transfer
rates
Generate less
heat and consume
less power
Last longer
33
USB flash drives plug into a USB port on a
computer or mobile device
34
35
A memory card is a removable flash memory
that you insert and remove from a slot in a
computer
CompactFlash
(CF)
microSD
Secure Digital
(SD)
Secure Digital
High Capacity
(SDHC)
microSDHC
xD Picture
Card
Memory Stick
Memory Stick
Micro (M2)
36
37
What are PC Cards?

Add capabilities to computer

Credit-card-sized device commonly
used in notebook computers
38
What is a smart card?


Stores data on
microprocessor
embedded in small card
Input, process, output,
and storage capabilities
39
Cloud Storage
40
41
What are advantages of an Internet
storage?
When in need
Large audio, video,
and graphics files can be
downloaded to an
Internet hard drive
Accessibility
Files can be accessed
from any computer or
device with Web access
Share
Others can be
authorized to access
data from your
Internet hard drive
Security
Allows offsite
backups of data
Reasons to subscribe to cloud storage:
Access files from any computer
Store large files
Allow others to access their files
View data and images
Store offsite backups
Provide data center functions
42
What are optical discs?
Push the button to
slide out the tray.

Flat, round, portable
discs made of metal or
plastic

Can be read only or
read/write

Most PCs include an
optical disc drive
Insert the disc,
label side up.
Push the same button
to close the tray.
43
How does a laser read data on an
optical disc?
disc label
lens
pit
0
prism
Step 1.
Laser diode
laser
shines a light
diode
beam toward
disc.
lightsensing
diode
lens
land
1
Step 2.
If light strikes
a pit, it
scatters. If light
strikes a land,
it is reflected
back toward
diode.
prism
lightsensing
diode
Step 3.
Reflected light
sends digital signals
of 1 to computer.
Absence of
reflected light is
read as digital
signal of 0.
laser
diode
44
How is data stored on an optical disc?


Data is stored in
single track
Track divided
into evenly
sized sectors
that store
items
single track
spirals to edge
of disc
disc sectors
45
How should you care for an optical disc?
46
What is the data transfer rate of a CD drive?
Ranges from
48X to 75X
75X
75  150 KBps = 11,250 KBps
or 12.25 MBps
X is 150 KBps
(KB per second)
48X:
48  150 KBps = 7,200 KBps
or 7.2 MBps
47
A CD-ROM can be read from
but not written to
A CD-R is an optical disc on
which users can write, but not
erase
A CD-RW is an erasable disc
48
What is a CD-ROM?




Compact disc read-only memory
Cannot erase or modify contents
Typically holds 650 MB to 1 GB
Commonly used to distribute multimedia and software
49
What are CD-Rs and CD-RWs?
Must have
CD recorder
or CD-R drive
CD-R (compact disc-recordable)
you can write on once
CD-RW (compact disc-rewritable)
disc you can write on
multiple times
Cannot erase
disc’s contents
Must have
CD-RW software
and CD-RW drive
50
What is a DVD-ROM (digital video disc-ROM)?


Must have DVD-ROM
drive or DVD player to
read DVD-ROM
Stores databases, music,
complex software, and
movies

Blu-Ray discs have storage
capacity of up to 100 GB

HD-DVD discs have
storage capacity of up to 60
GB
51
Other Types of Storage
52
What is a tape?
 Magnetically coated plastic ribbon
capable of storing large amounts
of data at low cost
 Used for backup
53
54
What is sequential access versus direct
access?
sequential access
Reading and writing data
consecutively
Method used for tape
direct access
You can locate a particular
data item or file immediately
Method used for hard disks,
and compact discs
Also called random access
How is data stored on a tape?
 Sequential access
 Reads and writes data consecutively, like music
tape
 Unlike direct access ( used on hard disks, CDs,
and DVDs ) which can locate particular item
much faster
55
A magnetic stripe card
contains a magnetic stripe that stores
information
A smart card
stores data on a microprocessor embedded in
the card
56
Microfilm and Microfiche
Store microscopic images of
documents on roll or sheet of
film
Images are recorded using
computer output microfilm
recorder
Microfilm — 100- to
215-foot roll of film
Microfiche — small sheet of
film, usually 4”  6”
57
58
Enterprise storage stores huge volumes
of data and information for large
businesses
Uses special hardware for heavy use,
maximum availability, and maximum
efficiency
59
To see the online addition
to the book click here