Computer
Architecture
How Does a Computer
Work?
Chapter 6
Student Learning Outcomes
1. Identify the system unit as well as the
motherboard with its components.
2. Define ASCII and describe how information is
represented inside a computer.
3. Describe the role of the CPU, RAM, and CPU
cycles in the functioning of a computer.
4. Define and explain the role of connectors, ports,
expansion buses, expansion cards, and
expansion slots.
5. Describe how you connect external devices to
your computer.
©2003 The McGraw-Hill Companies
Introduction
At one of the spectrum a computer can be
as big as a giant warehouse such as the
Cray X1. At the other end of the spectrum is
a tiny computer the size of a credit card
being developed by Sharp. No matter how
big or small computers are, they all have
certain characteristics in common.
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System Unit
• System unit is
the case or box
in which the
motherboard
and storage
units are
housed
p. 6.162 Fig. 6-1
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6.1 The Big Picture
Input
Data
Process
Data
Output
Information
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The System Unit
• Motherboard is the
large circuit board
inside your system
unit that holds the
CPU, memory, and
other essential
electronic
components
• CAN YOU NAME
THE PARTS?
SimNet
Concepts Support CD:
“The Motherboard” and “Inside the Computer”
p. 6.164 Fig. 6.3
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System Unit Terminology
Connector - plug
used to connect a device
to a computer
CPU – Chip that
carries out
instructions it
receives from the
software
Port – Place
through which
information and
instructions flow to
your computer
system
RAM – Temporary
memory that holds
software instructions
and information for
the CPU
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System Unit Terminology
Expansion Card –
Circuit board that is
inserted into an
expansion slot
Expansion Slot –
socket on the
motherboard into
which an expansion
card is inserted
Expansion Bus –
highway system that moves
information coming from
& going to devices
outside the motherboard
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6.2 Representing Information
Inside a Computer
• Binary digit (bit) has two states - 0 or 1
• By combining bits into groups of 8, we
can represent letters, symbols, and
numbers, like the word "cool" (below)
• A group of 8 bits represents one natural
language character and is called a byte
01000011
C
01001111
O
01001111
O
01001100
L
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ASCII, EBCIDIC, and
Unicode
• ASCII —American Standard Code for Information
Interchange
• Used on personal computers; eight-bit coding system; 256
different patterns
• EBCDIC —Extended Binary Coded Decimal Interchange
Code
• Used by IBM mainframes; eight-bit coding system; 256
different patterns
• Unicode —coding scheme capable of representing many
languages
• Usable on many computers; 16-bit coding system;
approximately 65,000 patterns
SimNet
Concepts Support CD: “Data Representation Using Binary Codes”
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ASCII & EBCDIC Binary
Representations
p. 6.168 Fig. 6.7
YOUR CHARACTERS
ASCII
EBCDIC
(space)
00100000
01000000
!
00100001
01011010
#
00100011
01111011
$
00100100
01011011
&
00100110
01010000
0
00110000
11110000
1
00110001
11110001
2
00110010
11110010
3
00110011
11110011
4
00110100
11110100
5
00110101
11110101
6
00110110
11110110
7
00110111
11110111
8
00111000
11111000
9
00111001
11111001
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6.3 CPU, RAM, and Machine
Cycles
• Central processing unit (CPU or
microprocessor or processor). Chip that carries
out instructions it receives from your software
• Random access memory (RAM) Temporary
memory that holds software instructions and
information for the CPU
• Machine cycle (CPU cycle or clock cycle)
consists of retrieving, decoding, and executing
the instruction, and returning the result to RAM
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Central Processing Unit
Chip that carries out instructions it receives
from your software
Role of the CPU is analogous to the role of
your brain – keeps everything functioning
as it’s supposed to
SimNet
Concepts Support CD: “The CPU”
p. 6.169 Fig. 6.3
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Random Access Memory (RAM)
Work being
OS Instructions
created
RAM Holds
Application
Keyboard
Software
Strokes & Mouse
instructions
Movements
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Machine Cycle (CPU Cycle)
1. Retrieve an
instruction
from RAM
4. Store the result
In RAM
Machine cycle consists of:
3. Execute the
instruction
2. Decode the
instruction
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How a CPU Works
p. 6.170 Fig. 6.9
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CPU Clock
– Sliver of quartz that beats at regular intervals in
response to an electrical charge
– CPU clock keeps all the computer’s operations
synchronized
– Each tick of the CPU clock is called a clock cycle
and is equivalent to a CPU cycle (machine cycle)
– CPU uses the CPU clock to keep instructions and
information flowing through your CPU at a fixed rate
SimNet
Concepts Support CD: “System Clock”
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CPU Clock
Each beat or tick of the
clock is called a CPU
cycle/machine cycle
CPU speed is quoted in
Megahertz (MHz = 1 million
CPU cycles per second) or
Gigahertz (GHz= 1 billiion
CPU cycles per second).
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Central Processing Unit
•
•
The faster a CPU is,
the more heat it
generates
A heat sink and a
fan are necessary to
cool the CPU down
CPU Cooling fan
CPU Heat Sink
p. 6.172 Fig. 6.11
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Classes of CPU’s
• Intel and AMD are two major
manufacturers of CPUs for consumer
computers
• CPU speed and power continue to get
faster
• Higher-performance CPUs have top
speeds and are the most expensive
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RAM Capacity
•
•
“Buy as much as you can afford”. For optimal
performance purchase, more than the
minimum specifications
512 MB is standard on new computers – i.e.
512 million bytes
SimNet
Concepts Support CD: “Memory”
p.6.173 Fig. 6.13
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RAM Capacity: How Much
Do You Need?
– Byte
– Kilobyte (KB)
– Megabytes (MB)
– Gigabytes (GB)
– Terabytes (TB)
– Petabyte (PB)
– Exabyte (EB)
= 8 bits
≈ 1 Thousand Bytes
≈ 1 Million Bytes
≈ 1 Billion Bytes
≈ 1 Trillion Bytes
≈ 1 quadrillion Bytes
≈ 1 quintillion Bytes
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RAM and Virtual Memory
• If your computer runs out of physical RAM
space, it uses hard disk space as
temporary RAM, which is called virtual
memory
• Virtual memory is slower than physical
RAM because instructions temporarily
stored on the hard disk must be moved
into RAM as they are needed
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How Virtual RAM Works
p.6.174 Fig. 6.14
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6.4 Making Connections
•
•
Ports are places in a computer system where external
devices are plugged in, and through which information and
instructions flow into the computer system
Connectors consist of cables that are used to join peripheral
to the computer. Common types of connectors:
•
USB
•
Firewire
•
Serial
•
PS/2
•
Parallel
•
RJ-45
p.6.175 Fig. 6.15
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USB Connectors and Ports
• USB (Universal serial bus) connector – is
a plug-and-play interface between a
computer and add-on device
• With plug and play, a new device can be
added to your computer without having to
add an adapter card or even having to turn
the computer off
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Firewire (IEEE 1394)
• Firewire (IEEE1394) although different
from USB, allows you to connect hotswap, plug and play devices to your
computer
• Firewire used mostly for video camcorders
and digital video disk (DVD) players
• A popular implementation of IEEE 1394 is
Sony’s I-LINK
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Serial Connectors and Ports
• Serial means one event at a time. It is
usually contrasted with parallel, meaning
more than one event happening at a time
• In the context of computer hardware and
data transmission, serial connection,
operation, and media usually indicate a
simpler, slower operation and parallel
indicates a faster operation
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Parallel Connectors and Ports
• On a PC, the printer is usually attached
through a parallel interface and cable so
that it will print faster
• Keyboard and mouse are one-way devices
that only require a serial interface and line
SimNet
Concepts Support CD: “Ports and Cables”
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Wireless Ports
• Wireless is a term used to describe
telecommunications in which
electromagnetic waves (rather than some
form of wire) carry the signal over part or
all of the communications path
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Wireless Ports – Cont.
• Common examples of wireless equipment
– Cellular phones
– Global positioning systems
– Cordless mouse
– Wireless networks
– Baby monitors
– TV remote controls
p.6.178 Fig. 6.17
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Wireless Ports
• IrDA (Infrared Data
Association) port
– Use infrared light to
send and receive
information
• Bluetooth uses radio
waves over distances
of up to 30 feet
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IrDA (Infrared Data Association)
• In this form of radio transmission, a focused ray
of light in the infrared frequency spectrum,
measured in terahertz, or trillions of hertz (cycles
per second), is modulated and sent from a
relatively short distance
• IrDa communications is playing an important
role in wireless data communication due to the
popularity of laptop computers, personal digital
assistants, digital cameras, mobile telephones,
pagers, and other devices
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Examples for Using IrDA
• Exchange business cards between
handheld PCs
• Send a document from a notebook
computer to a printer
• Coordinate schedules and telephone books
between a desktop and notebook computer
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Examples for Using IrDA
• Send faxes from a notebook computer to a
distant fax machine through a public
telephone
• Beaming images from a digital camera into
a computer
• Interconnecting local area networks.
Maximum effective distance is somewhat
under 1.5 miles
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Bluetooth
• Bluetooth is a computing and
telecommunications industry specification that
describes how mobile phones, computers, and
PDAs can easily interconnect with each other
and with home and business phones and
computers using a short-range wireless
connection
• Bluetooth requires that a low-cost transceiver
chip be included in each device
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Expansion Slots on the
Motherboard
SimNet
Concepts Support CD: “Expansion Cards and Slots”
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Buses
• Data buses
– Carries information in the form of bits around
the motherboard
– Two types: system and expansion
• System bus
– Electrical pathways which move information
between RAM and CPU
– The more bits that can travel together at one
time, the faster the bus
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Expansion Bus
• Moves information coming from and going
to devices outside the motherboard
• Types of expansion buses
– ISA (industry standard architecture)
– PCI (peripheral component interconnect)
– AGP (accelerated graphics port)
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PCI and AGP Busses
p.6.180 Fig. 6.19
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6.5 Notebook Computers
• Notebook computer is smaller and power to
run devices is limited
• Biggest advantage is its portability
• Electronic engineers work to reduce the
power and size requirements of these
computers
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Notebook Computers CPUs
and RAM
• Notebook hardware has
special features
• A mobile CPU is a
special type of CPU for a
notebook computer that
changes speed, and
therefore power
consumption, in response
to fluctuations in demand
• The CPU fan comes on
only when the CPU gets
too hot
• RAM for a notebook looks
a little different from
desktop RAM
Notebook RAM
Desktop RAM
p. 6.181 Fig. 6.13 & 6.20
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Notebook Computers –
Expansion Cards and Slots
• Devices are added to
a notebook by sliding
a PC card into the PC
Card slot on the
notebook, and
connecting the device
to the PC card
• A PC Card is the
expansion card used
to add devices to
notebook computers
p.6.181 Fig. 6.21
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6.6 Consumer Q&A
1. Why Does My USB Device Not Work
Right in My USB Port?
2. How Long Can I Expect My Notebook
Battery to Last?
3. How Do I Connect Multiple Devices to a
USB or Firewire Port?
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6.7 Key Terms
•
•
•
•
•
•
•
•
Bit
Bluetooth
Byte
Central processing
unit
Connector
CPU cache
Expansion bus
Expansion card
•
•
•
•
•
•
•
•
Expansion slot
Gigahertz (GHz)
IrDA
Machine cycle
Megahertz (MHz)
Mobile CPU
PC Card
PC Card Slot
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6.7 Key Terms
• Peripheral component
interconnect (PCI)
slot
• Port
• RAM
• System bus
• Virtual memory
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Review of Concepts
1. Working with Nibbles
 What’s less than a byte?
2. Comparing CPUs to the Human Body
3. Can You Identify Ports and
Components?
 Where would a DVD burner plug in?
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Hands On Projects
E-Commerce
1. Buying RAM
 Is your software running slower than it
should be?
2. Buying Devices with the Right
Connectors
3. Buying Music
 Get the best music from the Web
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Hands On Projects
Ethics, Security & Privacy
1. Business Computers Classify You as
Profitable – or Not
 Should they be able to?
 They want good customers – can computers
help find bad ones?
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Hands On Projects
on the Web
1. Compare Computer Systems
2. Getting the Right Video Card
 At what cost?
3. Find Out about Wireless Devices
 What’s available now?
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Hands On Projects
Group Activities
1. How Fast Is a Gigahertz?
 How long would it take you to blink a
gigahertz?
2. Visualize the Magnitude of Memory
 How many megabytes are in a football field?
3. Play CPU Cycle
4. What Type of Connectors Come on What
Devices?
©2003 The McGraw-Hill Companies