Technology in Action
Chapter 9
Behind the Scenes:
A Closer Look at System Hardware
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
1
Binary Language
• Computers work in binary language.
• Consists of two numbers: 0 and 1
• Everything a computer does is broken
down into a series of 0s and 1s.
• Switches: Devices inside the
computer that can be flipped between
these two states: 1 or 0, on or off
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Switches
• Nonmechanical
devices in computers
that open and close
circuits
• Types of electrical
switches
Vacuum Tube
– Vacuum tubes
– Transistors
• Solid state
Semiconductors
Transistors
– Integrated circuits
(very small transistors
billions per square inch)
Integrated Circuits
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3
Switches Representing Data
• The on/off state of a switch represents one
bit of data.
OFF
ON
• Bit (binary digit)
– On = 1
– Off = 0
0
1
OR
1
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= 1 bit
0
4
The Binary Number System
• Describes a number as powers of 2
• Also referred to as base 2 numbering
system
• Used to represent every piece of data
stored in a computer: all of the numbers,
letters, and instructions
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The Binary Number System
• Number systems are organized ways to
represent numbers.
• Each number in one system has a corresponding
number in another.
Binary
Base
10
128
2x64
64
2x32
32
2x16
16
2x8
8
2x4
4
2x2
2
2x1
1
0
1
0
1
1
0
0
1
0+
0+
0 + 64 + 0 +
16 + 8 +
1 = 89
01011001
=
89
Binary
Base 10
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The Binary Number System
• Any whole number can be precisely
represented (max 18,446,744,073,709,600,000)
•Fractions may not be precise
•Same problem as decimal numbers, for
example:
•What is 2/3 ? .6666666666→∞
•Solution: round to precision desired
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Representing Letters
and Symbols
• American Standard Code for Information
Interchange (ASCII)
– 8 bits = 1 byte = alphanumeric character or
symbol
– 256 different combinations
• Unicode
– 16 bits equal 1 byte or character
– 65536 different combinations; used to
define all alphabets
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ASCII Chart
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9
The CPU:
Processing Digital Information
• The brains of the
computer
• Different types of
CPUs
• Differentiating CPUs
– Processing power
– Clock speed and
cache
– Intel and AMD chips: Used
in most Windows-based
PCs and most newer Apple
systems
– Some older Apple systems
use a different CPU design
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10
Graphics Processing Unit (GPU)
• Performs the same
work as a CPU
• Specialized to handle
– 3D graphics
– Image processing
– Video processing
• CPUs perform better
with a GPU handling
graphics computation.
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11
The CPU Machine Cycle
• Fetch
– The next instruction is “fetched” from its location in
RAM and moved to the CPU.
• Decode
– The CPU circuitry is prepared to execute the
instruction.
• Execute
– The instruction is executed.
“Inside the Chip” by
Intel
Video Clip
• Store
– The results are stored in memory or registers.
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The System Clock
• Located on the motherboard
• Controls the CPU’s processing cycles
• Clock cycle
– Pulse or tick
• Clock speed
– Number of pulses per second
– Measured in hertz--Hz, megahertz--MHz,
gigahertz--GHz
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The Future of RAM
• Magnetoresistive Random Access
Memory (MRAM)
– Uses magnetic plates to store data
• Nano Random Access Memory (NRAM)
– Uses carbon nanotubes to store data
•
Something?? we don’t know about yet
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The Control Unit
The part of the CPU that:
• Manages the switches inside the CPU
• Is programmed by CPU designers to
remember the sequence of processing
stages for that CPU
• Moves each switch to its correct setting
(on or off)
• Then performs the work of that stage
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The Arithmetic Logic Unit (ALU)
• The Part of the CPU designed to perform
mathematical operations (addition,
subtraction, multiplication, division, etc.)
• Also performs logical OR, AND, and NOT
operations
• Is fed data from the CPU registers
– Word size: Number of bits a computer can
work with at a time (8, 16, 32, 64)
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Cache Memory-- more is better
• Small amount of very
fast memory located on
or near the CPU chip or
both
• Stores recent or
frequently used
instructions and data
• Used for quick access
by the CPU
• Different levels of
cache—L1 on chip, L2
off
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RAM--main memory, holds the
programs to be executed
• Volatile: When you turn off your
computer, the data is erased.
• Several kinds of RAM exist.
• Each type of RAM has a different
design.
– Some types work at much faster speeds.
– Some transfer data more quickly.
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Types of RAM: DRAM-dynamic ram
• Most inexpensive and most basic type of RAM
• Loses its electrical charge; needs to be refreshed
• Many types of DRAM
– SDRAM: Synchronous DRAM
– DDR SDRAM: Double data rate of SDRAM
– DDR2 SDRAM: Twice as fast as DDR SDRAM
– Dual-Channel DDR2: Faster than DDR2
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Types of RAM: SRAM
• Static RAM (SRAM)
– Does not lose its electrical charge
– Faster than DRAM (on CPU chip)
– More expensive than DRAM
– Used only in locations like cache
memory
– Used in thumb drives and other
pseudo-disks
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Buses: The CPU’s
Data Highway
• Bus
– Electrical pathway used to move data between
components
– Local bus or front side bus (FSB): Connects the CPU
with the memory
– Expansion bus: Connects the CPU with peripheral
controllers
– Bus speed improves with technology
01100010
01001000
01110011
00100111
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21
Bus Performance
• Bus clock speed
– Rate of speed data moves from one location to another
– Measured in MHz (millions of clock cycles per second)
• Bus width
– The number of bits of data moved on a bus at any one
time
– Measured in bits
• 16 bits
• 32 bits (PCI)
• 64 bits (PCI)
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Types of Expansion Buses
• ISA and EISA
– Found on older computers
– Connect mouse, modem, and sound card
• PCI and PCI-x
– Faster than ISA and EISA
– Found on modern computers
– Connect network, modem, and sound cards
• AGP (accelerated graphics port)
– Used for three-dimensional graphics
– Connects the graphics card and memory
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Making Computers Faster
• Pipelining: The CPU processes more than
one instruction at a time
Nonpipelined CPU
Instruction 1
Fetch
Decode
Execute
Store
Instruction 2
Fetch
Decode
Execute
Store
Pipelined CPU
Instruction 1
Fetch
Instruction 2
Decode
Fetch
Execute
Decode
Store
Execute
Store
Fetch
Decode
Execute
Store
Instruction 4
Fetch
Decode
Execute
Instruction 3
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Store
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Making Computers Faster
• Overclocking (can overheat and damage)
• Dual processing
– Two CPUs on the same system
– Each processor shares the workload
– Each could specialize—computing, communications
• Multi-core processing—sharing of workload, like
graphics, I/O
• Hyperthreading—1 CPU doing 2 or more tasks at the
same time, like math
• Parallel processing (Supercomputers)
– Network (or cluster) of computers
– Each computer works on a portion of the problem simultaneously
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