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How Computers Work Part 1 6 February 2008
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Sometimes They Don’t Having a Bad Day Mouse Won’t Work
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Simplified Model of a Computer
processor retrieves the instruction directs data movement Performs the operations Control Unit Arithmetic Logic Unit instructions data the information that it works on defines an algorithm MEMORY
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Computer Cycle Fetch Execute Store
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Logical organization of computer system
CPU Inputs Outputs programs data Memory information Programs & Data/info in use now Storage LOTS of programs and data files stored here
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Simplified Model of a Computer
processor retrieves the instruction directs data movement Performs the operations Control Unit Arithmetic Logic Unit instructions data the information that it works on defines an algorithm MEMORY
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Binary System 1 = Everyone knows that computers store bits, right?
What does it mean? All data is stored as a series of zeroes and ones Why? 1 =
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Representing Numbers Additive system Positional system ||||| |||||
Every item represents 1 Examples of additive systems? Positional system Value = face * place 37 = 3*10 + 7*1 ||||
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Positional System Base = number of different values in a position
Base 10 = 10 values: 0-9 Base 2 = 2 values: 0-1 Value of each position = power of base b4 b3 b2 b1 b0 Binary:
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Binary Positional System
= 1 2 3 4 1 =
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Examples Examples 1111 = 15 1000 = 8 = 100
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Exercises Find the decimal value of 1111 10111
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(place value) =0 =1 =2 =3 =4 =5 =6 =7 =8 =9 =10 =11 Etc.
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Making sense? 26 25 24 23 22 21 20 64 32 16 8 4 2 1 (place value)
(place value) Represent 37 in binary code? What about 63?
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Exercises Find the decimal value of 1111 10111
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Decimal Numbers represented logically in binary form
represented physically with bits
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Data Types Computer doesn’t know what the bits represents or what format is being used Computer assumes that the instructions know the format of the data What are the types of data? Numbers, text, pictures, sound, instructions
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Data Types Numbers: integers and floating point numbers (scientific notation) Why do we need floating point numbers? Text: Unicode, double byte Languages and symbols (Word insert symbol) Pictures: pixels A very fine needlepoint How to represent color? Sound: different formats Instructions
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