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page 6 of 9
The Bandwidth Tidal Wave
A
New Moore's Law?
Intel Chairman Gordon Moore recently promulgated a new Moore’s Law,
supposedly deflecting the course of the old Moore’s Law, which ordains
that chip densities double every 18 months. The new law is that the costs
of a chip factory double with each generation of microprocessor. Moore
speculated that these capital burdens might deter or suppress the necessary
investment to continue the pace of advance in the industry.
Gerhard (“Gerry”) Parker, Intel’s chief technical officer,
however, presents contrary evidence. The cost for each new structure may
be approximately doubling as Moore says. But the cost per transistor—and
thus the cost per computer function—continues to drop by a factor
of between three and four every three years. Not only does the number
of transistors on a chip rise by a factor of four, but the number of chips
sold doubles with every generation of microprocessor, as the personal
computer market doubles every three years. Thus there will be some eight
times more transistors sold by Intel from a Pentium fab that from a 486
fab. At merely twice the cost, the new fab seems a bargain.
Of course, Intel gets paid not for transistors but for computer functions.
To realize the benefits of the new fabs, therefore, Intel must deliver
new computer functions that successfully adapt to the era of bandwidth
abundance.
Moreover, it is worth noting that measured in telecosmic terms of useful
terabits per second of bandwidth, a MicroUnity fab ultimately costing
some $ 150 million might generate more added value than a $ 2 billion
megafab of Intel.
Return to Low and Slow
Since as a general rule, the more the power, the faster the switch, you
can get speed by using high-powered or exotic individual components. It
is an approach that worked well for years at Cray, IBM, NEC and other
supercomputer vendors. Wire together superfast switches and you will get
a superfast machine.
The other choice for speed is to use low-powered, slow switches. You make
them so small and jam them so close together, the signals get to their
destinations nearly as fast as the high-powered signals. This approach
works well in the microprocessor industry and in the human brain.
Despite occasional deviations at Cray and IBM, low and slow has been the
secret of all success in semiconductors from the outset. Inventor William
Shockley substituted slow, low-powered transistors for faster, high-powered
vacuum tubes. Gordon Teal at Texas Instruments replaced fast germanium
with slower silicon. Jean Hoerni at Fairchild spurned the fast track of
mountainous Mesa transistors to adopt a flat “planar” technology
in which devices were implanted below the surface of the chip. Jack Kilby
and Robert Noyce then substituted slow resistors and capacitors as well
as slow transistors on integrated circuits for faster, high-powered devices
on modules and printed circuit boards. Federico Faggin made possible the
microprocessor by replacing fast metal gates on transistors with slow
gates made of polysilicon. Frank Wanlass and others replaced faster NMOS
and PMOS technologies with the 1,000 times slower and 10 times lower-power
Complementary Metal Oxide Semiconductors (CMOS) that now rule the industry.
Low and slow finds its roots in the very physics of solid state, separating
the microcosm from the macrocosm. Chips consist of complex patterns of
wires and switches. In the macrocosm of electromechanics, wires were simple,
fast, cool, reliable and virtually free; switches were vacuum tubes, complex,
fragile, hot and expensive. In the macrocosm, the rule was economize on
switches, squander on wires. But in the microcosm, all these rules of
electromechanics collapsed.
In the microcosm, switches are almost free—a few millionths of a
cent. Wires are the problem. However fast they may be, longer wires laid
down on the chip and more wires connected to it translated directly into
greater resistance and capacitance and more needed power and resulting
heat. These problems become exponentially more acute as wire diameters
drop. On the other hand, the shorter the wires the purer the signal and
the smaller the resistance, capacitance and heat.
This fact of physics is the heart of microelectronics. As electron movements
approach their mean free path—he distance they can travel “ballistically”
without bouncing off the internal atomic structure of the silicon—they
get faster, cheaper and cooler.
At the quantum level, noise plummets and bandwidth explodes. Tunneling
electrons, the fastest of all, emit virtually no heat at all. It was a
new quantum paradox; the smaller the space the more the room, the narrower
the switches the broader the bandwidth, the faster the transport the lower
the noise. As transistors are jammed more closely together, the power
delay product—the crucial index of semiconductor performance combining
switching delays with heat emission—improves as the square of the
number of transistors on a single chip.
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