Technology in Action Alan Evans Kendall Martin Mary Anne Poatsy Ninth Edition Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall

Technology in Action Technology in Focus: Under the Hood Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall

Switches System unit –Box that contains central electronic components of the computer Computer system –Can be viewed as an enormous collection of on/off switches Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall2

Electrical Switches Computers work with numbers, not words –Binary language consists of two numbers: 0 or 1 –Electrical switches are devices that can be switched between 1 and 0 signifying “On” and “Off” –Computers are built from a huge collection of electrical switches Lock Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall3

Vacuum Tubes Allow or block flow of electrical current Take up a large amount of space Produce heat and burn out frequently Impractical because of size and reliability Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall4

Transistors Electrical switches built of layers of silicon Early transistors were built in separate units as small metal rods –Each rod was a small on/off switch Smaller and faster than vacuum tubes Produced less heat Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall5

Integrated Circuits –Support huge number of transistors –Also contain resistors, capacitors, and diodes –No more than ¼ inch in size –Over 2 billion transistors can fit on integrated circuit Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall6 Tiny regions of semiconductor material

Base 10 Number System ,000s place s place s place s place 6 * 1, * * * 1 (6,000) + (900) + (50) + (4) = 6,954 Base 10 uses 10 digits (0–9) To represent a number, you break it down into groups of ones, tens, hundreds, etc. Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall7

Base 2 Number System Base 2 or binary uses two digits (1,0) Describes value as sum of powers of 2: 1, 2, 4, 8, 16, 32, 64, and so on 2 3 8s place 2 2 4s place 2 1 2s place 2 0 1s place 1011 (8) + (0) + (2) + (1) = 11 Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall8

Base 16 Number System Hexadecimal notation is used to avoid working with long strings of 1s and 0s Base 16 uses 16 digits (0–9 and A–F) –A equals 10, B equals 11, etc. Values in hexadecimal are much shorter than binary –Easier for computer scientists to use 43 than Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall9

Windows Calculator Windows Calculator in Programmer view: Converts from decimal values to binary –67 is in binary Also converts to hexadecimal notation – 67 is 43 in hexadecimal Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall10

Representing Characters: ASCII American Standard Code for Information Interchange represents each letter or character as 8-bit binary code –Each binary digit is called a bit –8 binary digits (or bits) create one byte ASCII Code Represents This Symbol ASCII Code Represents This Symbol A a B b C C Z # ! $ “ % Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall11

Representing Characters: Unicode ASCII can use only 256 codes Unicode uses 16 bits and can represent nearly 1,115,000 code points Currently assigns more than 96,000 unique character symbols Unicode can represent alphabets of all modern and historic languages Will probably replace ASCII as standard Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall12

Representing Decimal Numbers IEEE established floating-point standard –Describes how numbers with fractional parts should be represented in binary –Uses a 32-bit system –First digit used to indicates whether number is positive or negative –Next 8 bits store magnitude (hundreds, millions, etc.) –Remaining 23 bits store value of number Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall13

CPU Machine Cycle All CPUs perform a series of similar steps –Fetch –Decode –Execute –Store Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall14

System Clock Moves CPU from one stage of the machine cycle to the next Acts as a metronome, keeping a steady beat or tick –Ticks, known as the clock cycle, set the pace –Pace, known as clock speed, is measured in hertz (Hz) Today’s speed is measured in gigahertz (GHz), one billion clock ticks per second Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall15

Control Unit Manages switches inside the CPU Remembers –Sequence of processing stages –How switches are set for each stage With each beat of system clock, control unit moves each switch to correct on or off setting and performs work of that stage Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall16

Stage 1: The Fetch Stage Data and program instructions are stored in various areas of computer system Program or data is moved to RAM from hard drive As instructions are needed, they are moved from RAM into registers –Storage areas located on CPU Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall17

Cache Memory Stores recent or frequently used instructions Faster access than RAM Advantage is better performance Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall18 Small blocks of memory located directly on and next to CPU chip

Stage 2: The Decode Stage CPU’s control unit decodes a program’s instructions into commands Instruction set –The collection of commands a CPU can execute –Written in assembly language –Assembly language is translated into machine language for the CPU Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall19

Stage 3: The Execute Stage Arithmetic logic unit (ALU) –Mathematical operations Addition Subtraction Multiplication Division –Test comparisons of values (, =) –Logical OR, AND, and NOT operations –Word size is bits worked with at a time Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall20

Stage 4: The Store Stage Results produced by the ALU in Stage 3 are stored in the registers Instruction explains which register to use When entire instruction is completed, the next instruction will be fetched The fetch-decode-execute-store cycle begins again Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall21

Making CPUs Even Faster Building a faster CPU is not easy Must consider time it will take to design, manufacture and test the processor To create CPU for release in 36 months, it must perform at least twice as fast as what is currently available Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall22

Moore’s Law Over 40 years ago, Moore predicted that the number of transistors on a processor would double every 18 months –Prediction has been remarkably accurate Manufacturers can increase CPU performance in several ways –Pipelining to boost performance –Specialized, faster instructions –Using CPUs with six processing paths Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall23

Pipelining Boosts CPU performance CPU works on more than one stage or instruction at a time 24Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall

Special Multimedia Instructions New processors incorporate multimedia instructions into the basic instruction set Multimedia-specific instructions work to accelerate video, speech, and image processing in the CPU Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall25

Multiple Processing Efforts Quad- processor has four separate CPU chips on one motherboard Multi-core processing –Dual-core processors have two separate parallel processing paths –Six-core processors are appearing in high- performance home-based systems Parallel processing uses multiple computers to work on portion of same problem simultaneously 26Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall

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