Computer: Definition and History
Lin ZhongELEC101, Rice University
What makes a computer?
What did you do to the NXT, indeed?
lab1.nxc
lab1.rxe
Compiler
Program as understood by NXT
What does it take NXT to achieve it?
• Interface to receive your instructions• Store your instructions• Execute your instructions– Sense– Calculate– Actuate
Computer: definition
• Programmable machine that receives input, stores and automatically manipulates data, and provides output in a useful format– Wikipedia
Elementary functions of computer
• Communication– Input– Output
• Storage
• Processing (calculation/manipulation)
Computer: definition
• Programmable machine that receives input, stores and automatically manipulates data, and provides output in a useful format– Wikipedia
Key features of computer
• Programmable– Take new instructions
• Automatic– Involving human as little as possible
• Useful– Serve a human purpose
Questions to answer
• Why does NXT accept instructions in 0s and 1s?
• How does NXT store instructions?
• How does NXT interpret the instructions?
Key concepts
• State, data, and information• Computing– How to store, change, and communicate
information• Analog signal vs. digital signal
• State in various incarnations
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State vs. Data vs. Information
• State– The physical property of a physical entity
• Data– State measurement properly represented
• Information– “Meanings” carried by signal/data– Can be measured (entropy)
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Objective
Subjective
Computing
• Human function– Process information– Store information– Communication information
• Physical realization– Modification (Processing) of a state– Storage of a state– Communication of a state
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The world is analog
• Analog states– Continuous in both time and amplitude– Temperature as example
• Practical challenges to analog state– For example, tell a friend about the classroom
temperature
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Analog to digital: Quantization
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Amplitude
TimeDiscrete value, continuous time
Why could the information loss be fine?
Analog to digital: Sampling
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Amplitude
TimeDiscrete time, continuous value
Why could the information loss be fine?
Digital signal
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Amplitude
Time
Discrete value, discrete time
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Era of mechanical states
Chinese abacus
Punched card based “computers”
• Two states: presence or absence of hole
Jacquard loom (1801)
• Punched cards control positions of hooks for weaving
• More: fairground organ, player piano,….,
Mechanical computer • Charles Babbage (1791-1871)
– Difference Engine– Analytical Engine
• First programmable computer• First programmer (Ada Lovelace)
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WWW
Mechanical calculator (1900s to 1960s)
241964
1958
251966
Problems with mechanical states
• To change a state
• To store a state
• To communicate a state
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