IEEE Spectrum August, 2009 - 34

A fAult-monitoring microprocessor design
cAn sAve power or Allow overclocking

by david blaauw & shidhartha das

CPU,
Heal Thyself

daniel bejar

In the old days, computer vendors would often

pull a fast one. They would tell you their system had the latest microprocessor when it actually had a cheaper, slower
version running faster than the chip's rating permitted. So
the shiny, new 500-megahertz system you thought you
were buying might contain only an overclocked 300-MHz
CPU. But the computer worked fine; indeed, it might have
operated perfectly for years, with you none the wiser.
And you perhaps replaced it only because a good buy on
a 1-gigahertz machine eventually came along.
How did that poor 300-MHz processor cope with such
abuse? The short answer is that the manufacturer had
set the clock speed low to ensure that its products would
function without fault despite the inevitable variations
among chips and among their different operating environments. Shady overclockers took advantage of that
conservatism, inviting unpredictable failures when they
eliminated the chipmaker's prudent safety margins.
Lately, overclocking has gone mainstream. You can, for
example, find competitions on the Web in which hardware
hackers vie for top honors in this domain. Even chip manufacturers themselves are doing it in public trials to show off
how blazingly fast their processors can run under the right
conditions-like when they are being cooled with liquid
helium to within a few kelvins of absolute zero.

www.spectrum.ieee.org

E ng i ne e r s at Adv a nc e d M ic r o
Devices, of Sunnyvale, Calif., did just
that this past April to prove that the
company's Phenom II CPU could break
the 7-GHz barrier. In theory, they could
have used the same approach to reduce
the voltage at which this chip runs at
its normal clock speed. That in turn
would have significantly diminished
the power it consumed.
While saving a few watts is not so
important in a desktop system, it's critical for smartphones, mobile Internet
devices, and other such gadgetry, which
now have to handle glitzy graphics,
video, Web access, and gaming without
burning too quickly through their tiny
batteries. And reducing the amount of
power that a CPU uses translates to an
enormous amount of money saved for
the companies that deploy vast numbers of microprocessors in large-scale
server farms.
The problem is that if you use anything less than their normal voltage, some
of these chips, on rare occasions, will fail
to produce the correct results. That might
happen when a laptop is turned on after

AuguSt 2009 * iEEE SpEctrum * NA

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http://www.spectrum.ieee.org

Table of Contents for the Digital Edition of IEEE Spectrum August, 2009

IEEE Spectrum August, 2009 - Cover1
IEEE Spectrum August, 2009 - Cover2
IEEE Spectrum August, 2009 - 1
IEEE Spectrum August, 2009 - 2
IEEE Spectrum August, 2009 - 3
IEEE Spectrum August, 2009 - 4
IEEE Spectrum August, 2009 - 5
IEEE Spectrum August, 2009 - 6
IEEE Spectrum August, 2009 - 7
IEEE Spectrum August, 2009 - 8
IEEE Spectrum August, 2009 - 9
IEEE Spectrum August, 2009 - 10
IEEE Spectrum August, 2009 - 11
IEEE Spectrum August, 2009 - 12
IEEE Spectrum August, 2009 - 13
IEEE Spectrum August, 2009 - 14
IEEE Spectrum August, 2009 - 15
IEEE Spectrum August, 2009 - 16
IEEE Spectrum August, 2009 - 17
IEEE Spectrum August, 2009 - 18
IEEE Spectrum August, 2009 - 19
IEEE Spectrum August, 2009 - 20
IEEE Spectrum August, 2009 - 21
IEEE Spectrum August, 2009 - 22
IEEE Spectrum August, 2009 - 23
IEEE Spectrum August, 2009 - 24
IEEE Spectrum August, 2009 - 25
IEEE Spectrum August, 2009 - 26
IEEE Spectrum August, 2009 - 27
IEEE Spectrum August, 2009 - 28
IEEE Spectrum August, 2009 - 29
IEEE Spectrum August, 2009 - 30
IEEE Spectrum August, 2009 - 31
IEEE Spectrum August, 2009 - 32
IEEE Spectrum August, 2009 - 33
IEEE Spectrum August, 2009 - 34
IEEE Spectrum August, 2009 - 35
IEEE Spectrum August, 2009 - 36
IEEE Spectrum August, 2009 - 37
IEEE Spectrum August, 2009 - 38
IEEE Spectrum August, 2009 - 39
IEEE Spectrum August, 2009 - 40
IEEE Spectrum August, 2009 - 41
IEEE Spectrum August, 2009 - 42
IEEE Spectrum August, 2009 - 43
IEEE Spectrum August, 2009 - 44
IEEE Spectrum August, 2009 - 45
IEEE Spectrum August, 2009 - 46
IEEE Spectrum August, 2009 - Cover3
IEEE Spectrum August, 2009 - Cover4
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