MIT6_004s09_lec02

MIT6_004s09_lec02 - MIT OpenCourseWare http:/ocw.mit.edu...

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MIT OpenCourseWare http://ocw.mit.edu For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . 6.004 Computation Structures Spring 2009
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L02 - Digital Abstraction 1 6.004 – Spring 2009 2/5/09 The Digital Abstraction Handouts: Lecture Slides 1. Making bits concrete 2. What makes a good bit 3. Ge±ing bits under contract modified 1/30/09 11:46 L02 - Digital Abstraction 2 6.004 – Spring 2009 2/5/09 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 – Spring 2009 2/5/09 Substrates for computation We can build upon almost any physical phenomenon… Wait! Those last ones might have potential. .. lanterns polarization of a photon dominos engraved stone tablets Billiard balls E. Coli L02 - Digital Abstraction 4 6.004 – Spring 2009 2/5/09 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 affected by environment DC connectivity required? R & C effects slow things down zero
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L02 - Digital Abstraction 5 6.004 – Spring 2009 2/5/09 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 – Spring 2009 2/5/09 Information Processing = Computation First let’s introduce some processing blocks: v Copy v INV v 1-v L02 - Digital Abstraction 7 6.004 – Spring 2009 2/5/09 Why have processing blocks? The goal of modular design: What does that mean anyway: Rules simple enough for a 6-3 to follow… Understanding BEHAVIOR without knowing IMPLEMENTATION Predictable composition of functions Tinker-toy assembly Guaranteed behavior, under REAL WORLD circumstances Abstraction L02 - Digital Abstraction 8 6.004 – Spring 2009 2/5/09 ?
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MIT6_004s09_lec02 - MIT OpenCourseWare http:/ocw.mit.edu...

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