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What is a computer?

A machine that processes information

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Processes Information

Input Computer Output

… but,

brains process information

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Why use computers?

Fast Accurate Don’t get bored Expand our capabilities

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At fundamental level

Computers work by transmitting an electric current through switches

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Components

Calculator Computer

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Input devices

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Output Devices

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Temporary Memory

Calculator Small Intermediate

values Explicit memory

Computer Bigger Main memory

Power off Information lost

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Storage

Calculator none

ComputerBig external storage Floppy disks Hard disks Optical disks Magnetic tape Flash memory

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Processor

Calculator Single purpose Few functions Hardwired

Computer General purpose Programmable

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Processor

Performs (executes, carries out) a sequence of instructions

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What instructions

Arithmetic: + - * / Compare 2 data values and use the

result to alter the order of execution Move data (e.g. from memory to

processor)

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Program: A sequence of instructions

Stored program computer: processor gets the data AND the instructions from main memory

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Summary

Computer Programmable More I/O options Bigger memory Storage Faster Stores both programs and data in

memory

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See overhead