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TECHNOLOGY IN ACTION
Technology in Focus
Under the Hood
Switches and Number Systems
Electrical Switches
• Computer system
• Enormous collection of on/off switches
• Combined to perform addition, subtraction, and move data
around
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Switches and Number Systems
Electrical Switches
• Computers only understand two states
• Binary language consists of two numbers: 1 or 0
• Electrical switches can be switched between 1 and 0
signifying ON and OFF
• Computers contain a huge
collection of electrical
switches
Lock
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Switches and Number Systems
Vacuum Tubes
• Used as switches
• Earliest generation computers
• Allow or block flow of electrical
current
• Problems with vacuum tube
switches
• Take up a large amount of space
• Produce heat and burn out
frequently
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Switches and Number Systems
Transistors
• Electrical switches built of layers of materials called
semiconductors
• Semiconductors can be controlled to conduct or insulate
• Made from silicon
• Smaller and faster than vacuum tubes
• Produce less heat, can be switched quickly, and are
less expensive
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Switches and Number Systems
Transistors
• This silicon wafer has the transistor circuitry for
hundreds of devices etched on it
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Switches and Number Systems
Integrated Circuits
• Tiny regions of semiconductor material
• Support a huge number of transistors
• No more than ¼ inch in size
• Can fit billions of transistors
• CPUs are microprocessor chips
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Switches and Number Systems
Number Systems
• Base-10 number system
• Number system is an organized plan for representing a
number
• Decimal notation
• Base 10 uses 10 digits (0–9)
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Switches and Number Systems
Number Systems
• Base-2 or binary uses two digits (0 and 1)
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Switches and Number Systems
Number Systems
• Hexadecimal notation
• Used to avoid working
with long strings of 1s
and 0s
• Base-16 uses 16 digits
(0–9 and A–F)
• A = 10, B = 11, etc.
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Switches and Number Systems
Number Systems
• American Standard Code for Information
Interchange (ASCII) represents each letter
or character as 8-bit binary code
• Each binary digit
is a bit
• 8 binary digits
(or bits) create
one byte
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Switches and Number Systems
Number Systems
• Unicode
• ASCII can only
assign 256 unique
codes
• Not sufficient for all
languages
• Unicode uses 16
bits
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Switches and Number Systems
Number Systems
• IEEE established floating-point standard
• Describes how fractional parts should be represented in
binary
• Uses a 32-bit system
• First digit indicates whether a number is positive or
negative
• Next 8 bits store magnitude
• Remaining 23 bits store value of number
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How the CPU Works
The Machine Cycle
• Machine cycle refers to series of general steps CPU
performs
1. Fetch
2. Decode
3. Execute
4. Store
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How the CPU Works
The Control Unit and the System Clock
• Manages switches inside CPU
• Remembers:
• Sequence of processing stages
• How switches are set for each stage
• With each beat of the system clock
• Control unit moves each switch to correct on/off setting
• Performs the work of that stage
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How the CPU Works
The Control Unit and the System Clock
• Moves CPU from one stage to the next
• Acts as a metronome, keeping steady beat or tick
• Ticks, known as the clock cycle, set the pace
• Pace, known as clock speed, is measured in hertz
• Today’s speed is measured in gigahertz, 1 billion
clock ticks per second
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How the CPU Works
Machine Cycle Stages
• The fetch stage
• Data and program instructions stored in various areas of
the system
• Program or data is moved to RAM from the hard drive
• As instructions are needed, they are moved from RAM into
registers
• Storage areas located on CPU
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How the CPU Works
Machine Cycle Stages
• The decode stage
• CPU’s control unit decodes program’s instructions into
commands
• Instruction set
• Commands CPU can execute
• Written in assembly language
• Assembly language translated into binary code
• Machine language—long strings of binary code
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How the CPU Works
Machine Cycle Stages
• The execute stage
• Arithmetic logic unit (ALU)
• Mathematical operations
• Test comparisons of values (<, >, =)
• Logical OR, AND, and NOT operations
• Word size is number of bits worked
with at a time
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How the CPU Works
Machine Cycle Stages
• The store stage
• Results produced by ALU are stored in registers
• Instruction explains which register to use
• When instruction is completed, the next
instruction will be fetched
• The fetch–decode–execute–store cycle begins
again
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Making CPUs Even Faster
• Building a faster CPU is not easy
• Must consider time to design, manufacture, and test
the processor
• For release in 36 months, a CPU must perform twice
as fast as currently available
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Making CPUs Even Faster
Pipelining
• CPU works on more than one stage or
instruction at a time
• Boosts CPU performance
• System clock indicates when instructions
move to next process
• Can potentially run four times faster
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Making CPUs Even Faster
Pipelining
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Making CPUs Even Faster
Specialized Multimedia Instructions
• Incorporates specialized multimedia instructions in the
command set
• Speeds up video and audio processing
• Advanced Encryption Standard (AES)
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Making CPUs Even Faster
Multiple Processing Efforts
• Many high-end server systems use a large number of
processors
• Multicore processing
• Quad-core processors have four separate parallel
processing paths
• Six- and eight-core processors are available
• Parallel processing uses multiple computers to work
on a portion of same problem simultaneously
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Questions
Copyright
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without the prior written permission of the publisher. Printed in the United States of America.