the science that drives modern computers. cos 116: 4/8/2008 sanjeev arora
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The science that drives modern computers.
COS 116: 4/8/2008Sanjeev Arora
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Changing face of manufacturing
1936 Late 20th century
“Modern Times” Silicon wafer fabrication
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20th century science and IT: a match made in heaven?
“These are the days of miracles and wonders.” – Paul Simon, Graceland
Main theme in this lecture:
Scientific Advances Ability to control matter precisely Amazing products/computers
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Quantum mechanics (wave-particle duality, quantization of energy, etc.)
Ability to create light of a single frequency (“laser”)
Example of precise control of matter: Lasers
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Why lasers are so useful: Accurate focusing White light
Different colors focus at different points – “smudge”
Laser
Focus at single point
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Silicon Chip manufacturing
“A picture is worth a billion gates.”
Fact: Modern chips are manufactured using a process similar to photography
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Timeline
Vacuum Tube Triode (1908)
Transistor1947(silicon, germanium)
Very Large ScaleIntegrated (VLSI)Circuits; 1970s--(> 1,000 transistorsper chip)
Intel Itanium (Tukwila) 2008: 2 billion transistors
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Moore’s Law
Technology advances so that number of gates per square inch doubles every 18 months.
[Gordon Moore 1965]
Number of gates doubling every 24 months
Number of gates doubling every 18 months
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Implementation 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 junction
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Example: an AND gate
N
NPA
B
Power
Output
Ground
N
NP
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Chip Fabrication
Grow silicon ingots
Cut wafers and polish Create mask
Coat 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 it
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Aside: Lasik eye correction
Uses laser invented for chip fabrication
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Chip Packaging
Inside Outside
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Life cycle of a microprocessor
Fact: Less than 1% of microprocessors sold are used in computers
Inside an iPod Remote
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Why so few new CPU’s?
Cost of new design: $8 billionProfit: $100 / chipNeed to sell 80 million to break even
Cost of new design: $8 billionProfit: $100 / chipNeed to sell 80 million to break even
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Engineering tradeoffs
36 months later...
Can run at twice the clock speed! (Why?) But: higher clock speeds much more heat!
Half the size!
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Even more precise control of matterNanotechnology: manufacture of objects (machines, robots, etc.)at the atomic or molecular level (1-100 nanometers)
“nanogear”
Biocomputing: Implementing computers via interactions ofbiological molecules.
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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/s
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Total Internal Reflection
Porro Prism
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How optical fibers work
Glass fiber: 10-40 billion bits/s
“Total internal reflection”
PulsingLaser beam
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Transmission rates of trillion (“Tera”) bits/s
Wave Division Multiplexing (WDM)
Multiplexor De-multiplexor
Multiple (100 or so) data streams enter
One beam with various frequencies mixed in
Multiple data streams exit
Fiber optic cable
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Thoughts about the 20th century
What factors (historical, political, social) gave rise to this knowledge explosion?
Will it continue in the future?As we know,
There are known knowns.There are things we know we know.
We also knowThere are known unknowns.
That is to sayWe know there are some things
We do not know.But there are also unknown unknowns,
The ones we don't knowWe don't know.
— D. Rumsfeld, Feb. 12, 2002
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Are faster chips the answer to all problems in computing?
An Answer: No! Halting problem is undecidable!
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What about this decidable problem?
Does it 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)
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Next time:
Computer Viruses, Worms, and Zombies