82713 intro cs420 10 how to make switches use

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Unformatted text preview: ff 8/27/13 cs420: intro 7 Lets use them crea3vely Output is high if both the inputs input1 AND input2 are high Input 1 Outp ut If either of the inputs is low, the output is low. This is called an AND gate Input 2 Now, can you make an OR gate with switches? 8/27/13cs420: intro 8 OR Gate Input1 Output Input2 Output is low iff both inputs are low 8/27/13 cs420: intro I.e. Output is high if either of the inputs (or both) are high (input1 OR input2) 9 Basic Gates •  There are three basic kinds of logic gates Operation: AND of two inputs OR of two inputs NOT (complement) on one input Logic gate: • Two Questions: • How can we implement such switches? • What can we build with Gates? •  Adders, controllers, memory elements, computers! 8/27/13 intro cs420: 10 How to make switches? •  Use mechanical power •  Use hydrolic pressure •  Use electromechanical switches (electromagnet turns the switch on) •  Current technology: –  Semiconductor transistors •  A transistor can be made to conduct electricity depending on the input on the 3rd input –  CMOS “gates” (actually, switches) Two properties of Switches and Gates: Size 8/27/13 cs420: intro 11 Switching and Propagation delay Clock Speeds •  Since we can make transistors smaller –  Which means smaller capacitances.. •  Imagine Pilling up “tanks” with “water” (electrons) •  We can turn them on or off faster –  Which means we can make our computers go faster –  Clock cycle is selected so that the parts of the computer can Pinish basic calculations within the cycle –  And indeed: 8/27/13 cs420: intro 12 The Virtuous Cycle •  If you can make transistors smaller, –  You can Pit more of them on a chip •  Cost per transistor decreases –  AND: propagation delays get smaller •  So they can run faster! •  Can you make them smaller? –  Technological progress needed, but can be done •  This led to: –  Cheaper and faster processors every year 8/27/13 cs420: intro 13 Moore’s law •  Commonly (mis) stated as –  “Computer Performance doubles every 18 months” •  Gordon Moore observed in 1965 –  “The complexity… has increased roughly a factor of two per year. [It] can be expected to continue…for at least 10 years” –  Its about number of transistors per chip •  Funny thing is: it held true for 40+ years –  And still going until 2020 –  “Self FulPilling prophecy” 8/27/13 cs4...
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