Computer: Definition and History Lin Zhong ELEC101, 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 13

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) 14 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 15

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 16

Analog to digital: Quantization 17 Amplitude Time Discrete value, continuous time Why could the information loss be fine?

Analog to digital: Sampling 18 Amplitude Time Discrete time, continuous value Why could the information loss be fine?

Digital signal 19 Amplitude Time Discrete value, discrete time

20 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 ( ) – Difference Engine – Analytical Engine First programmable computer First programmer (Ada Lovelace) 23 WWW

Mechanical calculator (1900s to 1960s)

Problems with mechanical states To change a state To store a state To communicate a state 26