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Unformatted text preview: L02 - Digital Abstraction 1 6.004 – Fal 2010 9/14/10 The Digital Abstraction Handouts: Lecture Slides 1 1. Making bits concrete 2. What makes a good bit 3. Ge ing bits under contract L02 - Digital Abstraction 2 6.004 – Fal 2010 9/14/10 Concrete encoding of information To this point we’ve discussed encoding information using bits. But where do bits come from? If we’re going to design a machine that manipulates information, how should that information be physically encoded? What makes a good bit? - cheap (we want a lot of them) - stable (reliable, repeatable) - ease of manipulation (access, transform, combine, transmit, store) He said to his friend, "If the British march By land or sea from the town to-night, Hang a lantern aloft in the belfry arch Of the North Church tower as a signal light,-- One if by land, and two if by sea; And I on the opposite shore will be, Ready to ride and spread the alarm Through every Middlesex village and farm, For the country folk to be up and to arm." L02 - Digital Abstraction 3 6.004 – Fal 2010 9/14/10 Substrates for computation We can build upon almost any physical phenomenon… Wait! Those last ones might have potential... h p://www.pinkandaint.com/oldhome/comp/dominoes/ h p://www.americanscientist.org/template/AssetDetail/assetid/14340 h p://www.digitalphilosophy.org/physicists_model.htm lanterns polarization of a photon dominos engraved stone tablets Billiard balls E. Coli L02 - Digital Abstraction 4 6.004 – Fal 2010 9/14/10 But, since we’re EE’s… Stick with things we know about: voltages phase currents frequency This semester we’ll use voltages to encode information. But the best choice depends on the intended application... Voltage pros: easy generation, detection lots of engineering knowledge potentially low power in steady state Voltage cons: easily a ff ected by environment DC connectivity required? R & C e ff ects slow things down zero L02 - Digital Abstraction 5 6.004 – Fal 2010 9/14/10 Representing information with voltage Representation of each point (x, y) on a B&W Picture: 0 volts: BLACK 1 volt: WHITE 0.37 volts: 37% Gray etc. Representation of a picture: Scan points in some prescribed raster order… generate voltage waveform How much information at each point? L02 - Digital Abstraction 6 6.004 – Fal 2010 9/14/10 Information Processing = Computation First let’s introduce some processing blocks: v Copy v INV v 1-v L02 - Digital Abstraction 7 6.004 – Fal 2010 9/14/10 Why have processing blocks?...
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