The science that drives modern computers.Changing face of manufacturing20th century science and IT: a match made in heaven?Moore’s LawWhy lasers are so useful: Accurate focusingSilicon Chip manufacturingImplementation of a gate in a modern chipExample: Implementing an AND gateChip FabricationAside: Lasik eye correctionChip PackagingLife cycle of a microprocessorWhy so few new CPU’s? Engineering tradeoffsEven more precise control of matter: NanotechnologyYet another example of control of matter: the changing data cableHow optical fibers workWave Division Multiplexing (WDM)Thoughts about the 20th centuryAre faster chips the answer to all problems in computing?What about this decidable problem?A week from today: The computational cost of automating serendipityNext lecture (do not miss!)The science that drives modern computers.COS 1164/10/2006Instructor: Sanjeev AroraChanging face of manufacturing1936 Late 20thcentury“Modern Times”Silicon wafer fabrication20thcentury science and IT: a match made in heaven?“These are the days of miracles and wonders.” – Paul Simon, GracelandMain theme in this lecture: Scientific AdvancesÆ Ability to control matter preciselyÆ Amazing products/computersMoore’s Law [Gordon Moore 1965] Technology advances so that number of gates per square inch doubles every 18 months.Number of gates doubling every 24 monthsNumber of gates doubling every 18 months Quantum mechanics (wave-particle duality, quantization of energy, etc.) Ability to produce light with a single frequency (“laser”)Example of precise control of matter: LasersWhy lasers are so useful: Accurate focusing White light Different colors focus at different points –“smudge” Laser Focus at single pointSilicon Chip manufacturing“A picture is worth a billion gates.”Fact: modern chips are manufactured using a processsimilar to photographyImplementation of a gate in a modern chip Semiconductor: not as good a conductor as metals, not as bad as wood Example: silicon Doped semiconductor: semiconductor with some (controlled) impurities: p-type, n-type Switch: p-n junctionExample: Implementing an AND gateNNPABPowerOutputGroundNNPChip FabricationGrow silicon ingotsCut wafers and polishCreate maskCoat with chemicals that remove parts unexposed to light Repeat to add metal channels (wires) and insulation; many layers Coat wafer with light sensitive chemicals and project mask onto itAside: Lasik eye correctionUses laser that was invented for chip fabricationChip Packaging Inside OutsideLife cycle of a microprocessorFact: Less than 1% of microprocessors sold are used in computersInside an iPod Remote(see sheet being passed around)Why so few new CPU’s?Cost of new design: $8 billion Profit: $100 / chip Need to sell 80 million to break evenEngineering tradeoffs36 months later... Can run at twice the clock speed! (Why?) But: higher clock speeds → much more heat!Half the size!Even more precise control of matter: NanotechnologyTechnology to manufacture objects (machines, robots, etc.)at the atomic or molecular level (1-100 nanometers)nanogearYet another example of control of matter: the changing data cable Serial cable: 115 kb/s USB cable: 480 Mb/s (USB 2.0) Fiber optic cable: 40 Gb/sHow optical fibers work Glass fiber: 10-40 billion bits/s“Total internal reflection”PulsingLaser beam Transmission rates of trillion (“Tera”) bits/sWave Division Multiplexing (WDM)MultiplexorDe-multiplexorMultiple (100 or so) data streams enterOne beam with various frequences mixed inMultiple data streams exitFiber optic cableThoughts about the 20thcentury What factors (historical, political, social) gave rise to this knowledge explosion? Will it continue in the future?What do we not know, and what do we not know we don’t know? (D. Rumsfield)Are faster chips the answer to all problems in computing?An Answer: No! Halting problem is undecidable!What about this decidable problem?Does this formula have a satisfying assignment? What if instead we had 100 variables? 1000 variables?(A + B + C) · (D + F + G) · (A + G + K) · (B + P + Z) · (C + U + X)A week from today: The computational cost of automating serendipityDiscussion topic:What is the difference between being creative and being able to appreciate creativity?Next lecture (do not miss!)How computation and computational models pervade
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