Superconducting Technology Assessment - nitrd

1.2 LIMITATIONS OF CONVENTIONAL TECHNOLOGY FOR HIGH-END COMPUTING
In 1999, the President’s Information Technology Advisory Committee (PITAC) wrote the following in its Report
to the President-Information Technology Research: Investing in Our Future (Feb 1999): “…Ultimately, silicon chip
technology will run up against the laws of physics. We do not know exactly when this will happen, but as devices
approach the size of molecules, scientists will encounter a very different set of problems fabricating faster
computing components.”
1.2.1 CONVENTIONAL SILICON TECHNOLOGY NOT THE ANSWER
NSA experts in HEC have concluded that semiconductor technology will not deliver the performance increases that
the government’s computing applications demand. Complementary metal oxide semiconductors (CMOS) is becoming
less a performance technology—vendors such as Intel are voicing reluctance to seek 10 GHz clock speeds—and
more a capability technology, with transistor counts of several hundred million per chip. The high transistor counts
make it possible to put many functional units on a single processor chip, but then the on-chip functional units must
execute efficiently in parallel. The problem becomes one of extracting parallelism from applications so that the
functional units are used effectively.
Unfortunately, there are applications for which on-chip parallelism is not the solution; for such applications, blazing
speed from a much smaller number of processors is required. For supercomputers, continuing reliance solely on a
CMOS technology base means a continuation of the trend to massively parallel systems with thousands of processors.
The result will be limitations in efficiency and programmability.
In addition, at today’s scale, the electrical power and cooling requirements are facing practical limits, even if ways
were found to efficiently exploit the parallelism. For example, the Japanese Earth Simulator system, which has been
ranked number one on the list of the top 500 installed HEC, consumes over 6 megawatts of electrical power.
1.2.2 SUPERCOMPUTING RSFQ A VIABLE ALTERNATIVE
The Silicon Industry Association (SIA) International Technology Roadmap for Semiconductors (ITRS) 2004 update on
Emerging Research Devices has many candidate technologies presently in the research laboratories for extending
performance beyond today’s semiconductor technology. Superconducting Rapid Single Flux Quantum (RSFQ) is
included in this list and is assessed to be at the most advanced state of any of the alternative technologies. RSFQ
technology has the potential to achieve circuit speeds well above 100 GHz with lower power requirements than
complementary metal oxide semiconductor (CMOS), making it attractive for very-high-performance computing, as
shown in Figure 1-1.
Superconducting RSFQ is assessed to be at the most advanced
state of any of the alternative technologies.
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