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Executive Summary
By definition, supercomputers are those hardware and software computing systems that provide close
to the best currently achievable sustained performance. The performance of supercomputers, which is
normally achieved by introducing parallelism, is typically much better than that of the vast majority of
installed systems. Supercomputers are used to solve complex problems, including the simulation and
modeling of physical phenomena such as climate change, explosions, or the behavior of molecules; the
analysis of data from sources such as national security intelligence, genome sequencing, or astronomical
observations; or the intricate design of engineered products. Their use is important for national security
and defense, as well as for research and development in science and engineering.
As the uses of computing have increased and broadened, supercomputing has become less dominant
than it once was. Many interesting applications require only modest amounts of computing, by today's
standards. Because of the increase in computer processing power, many problems whose solution once
required supercomputers can now be solved on relatively inexpensive desktop systems. That change has
caused the computer industry, the research and development community, and some government agencies
to reduce their attention to supercomputing. Yet problems remain whose computational demands for
scaling and timeliness stress even our current supercomputers. Many of those problems are fundamental
to the government's ability to address important national issues. One notable example is the Department
of Energy's computational requirements for nuclear stockpile stewardship.
The government has sponsored studies of a variety of supercomputing topics over the years. Some of
those studies are summarized in the body of this report. Recently, questions have been raised about the
best ways for the government to ensure that its supercomputing needs will continue to be satisfied in
terms of both capability and cost-effectiveness. To answer those questions, the National Research
Council's Computer Science and Telecommunications Board convened the Committee on the Future of
Supercomputing to conduct a 2-year study to assess the state of supercomputing in the United States and
to give recommendations for government policy to meet future needs. This study is sponsored jointly by
the Department of Energy's Office of Science and by its Advanced Simulation and Computing (ASC)
Program.
This interim report, presented approximately 6 months after the start of the study, reflects the
committee's current understanding of the state of U.S. supercomputing today, the needs of the future, and
the factors that contribute to meeting those needs. After such a short time, the committee is not yet ready
to comment in detail on the specifics of existing supercomputing programs or to present specific findings
and well-supported recommendations. Although the committee has made considerable progress in
understanding the current state of supercomputing and how it got there, it still has much more work to do
before it develops recommendations.
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2
THE FUTURE OF SUPERCOMPUTING: ANINTERIMREPORT
Many technical, economic, and policy issues need to be addressed in this study. They include (1) the
computational needs of present and future applications and approaches to satisfying them; (2) the
balancing of commodity components and custom design in supercomputer architectures and the effects of
software design improvements and industry directions on that balance; (3) the interplay of research,
development, prototyping, and production in creating innovative advances; (4) the extent and nature of
direct government involvement to ensure that its needs are met; and (5) the important requirement that the
present not be neglected while the future is being determined. Although this report touches on each of
those topics, the committee has not completed its consideration of them.
The particular technical approaches of any program that develops or uses supercomputing represent a
complex compromise between conflicting requirements and an assessment of risks and opportunities
entailed in various approaches. An evaluation of these approaches requires a detailed understanding of
(1) the relevant applications, (2) the algorithms used to solve those application problems, (3) the
performance likely to be achieved by codes that implement these algorithms on different platforms, (4)
the coding efforts required by various approaches, (5) the likely evolution of supercomputing technology
over multiple years under various scenarios, and (6) the costs, probabilities, and risks associated with
different approaches. In its final report, the committee will seek to characterize broadly the requirements
of different application classes and to examine the architecture, software, algorithm, and cost challenges
and trade-offs associated with these application classes keeping in mind the needs of the nuclear
stockpile stewardship program, the broad science community, and the national security community.
(Note that a separate, classified report by the JASONs is expected to identify the distinct requirements of
the stockpile stewardship program and its relation to the ASC acquisition strategy.) The committee
believes that it would be unwise to significantly redirect or reorient current supercomputing programs
before careful scientific consideration has been given to the issues described above. Such changes might
be hard to reverse, might reduce flexibility, and might increase costs in the future.
In the period ahead, the committee will continue to learn and to analyze. A workshop focused on
applications, to be held in the fall of 2003, will include a number of applications experts from outside the
committee. Its purpose will be to identify both the computational requirements of important applications
and the opportunities to adapt and evolve current solutions so as to benefit from advances in algorithms,
architectures, and software. In addition, the committee will meet with experts who are developing
solutions for applications of particular importance for national defense and security within the
Department of Energy (DOE) and the National Security Agency (NSA). The committee will also meet
with managers of supercomputing facilities, procurement experts, industrial supercomputer suppliers,
experts on computing markets and economics, and others whose expertise will help to inform it.
SUPERCOMPUTING TODAY
According to the June 2003 list of the 500 most powerful computer systems in the world, the United
States leads the world in the manufacture and use of supercomputers, followed by Japan. A number of
other countries make or use supercomputers, but to a much lesser degree.
Virtually all supercomputers are constructed by connecting large numbers of compute nodes, each
having one or more processors and a common memory, by an interconnect network (a switch).
Supercomputer architectures differ in the design of their nodes, their switches, and the node-switch
interfaces. Higher node performance is achieved by using commercial scalar microprocessors with 64-bit
data paths intended primarily for commercial servers or nodes designed specially for supercomputing,
rather than the high-volume, 32-bit scalar microprocessors used in workstations and lower capability
cluster systems. The custom nodes tend to use special mechanisms such as vectors or multithreading to
reduce memory latency rather than relying solely on the more limited latency avoidance afforded by
caches. High-bandwidth, scalable interconnects are typically custom-built and more expensive than the
lithe TOP500 list is available at .
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EXECUTIVE SUMMARY
more widespread Ethernet interconnects. Custom switch use is often augmented by custom node/switch
interfaces.
The highest-ranked system in the TOP500 list is the Japanese-built Earth Simulator, released in the
spring of 2002 and designed specifically to support geoscience applications. That system has custom
multiprocessor vector-based nodes and a custom interconnect. The emergence of that system has been
fueling recent concerns about continued U.S. leadership in supercomputing.
The system software that is used on most contemporary supercomputers is some variant of Unix,
either open source or proprietary. Programs are written in FORTRAN, C, and C++ and use a few
standard application libraries. All of these supercomputers use implementations of the message passing
interface (MPIN standard to sunnort messa~e-nassin~-stvle internode communication. Relativelv little
~ ~ — O ~ O
stanclarcllzatlon exists tor other aspects ot software environments and tOOlS.
EVOLUTION IN SUPERCOMPUTING
A major policy issue for supercomputing is the proper balance between investments that exploit and
3
evolve current supercomputmg architectures and software tine evolutionary aspect' and Investments in
alternative approaches that may lead to a paradigm shift (the innovative aspect). Both aspects are
important.
At this stage in the study, the committee sees the following advantages for an evolutionary approach
to investment and acquisition. First, much useful work is getting done using the existing systems, and
their natural successors can be expected to continue that work. In addition, there are no obvious near-
term architectural alternatives: The promising technology breakthroughs, such as processor-in-memory,
streaming architectures, and the like, that might revolutionize supercomputing are far off in the future and
less than certain. Of course, higher capability would enable better solutions to be obtained faster. But
history suggests that even when revolutionary advances come along, they do not immediately supplant
existing architectures. Different problems benefit from different architectures and no one design is
universally best. The committee sees a need for evolutionary investments in all major approaches to
supercomputing that are currently pursued: clusters built entirely of commodity components; scalable
systems that reuse commodity microprocessors together with custom technology in the interconnect or the
interconnect interface; and systems in which microprocessors, the interconnect, and their interface are all
customized.
Although some advantages also accrue from evolutions in software, the committee sees a need for
investment that would accelerate that evolution. The advantages of commodity architectural components
might be more easily realized if more applications were redesigned, better custom software was provided,
and the cost of bringing software to maturity was better appreciated. The benefit of software investment
is that it tends to have continuing value as architectures evolve. At the same time, both the maintenance
and the evolution of legacy applications must be anticipated and supported.
Finally, the committee observes that uncertainties in policy and inconsistencies over time can be both
disruptive and expensive. Unexpected pauses in an acquisition plan or failure to maintain a diversity of
suppliers and products can cause both the suppliers and the skilled workforce to divert their attention from
supercomputing. It can be difficult and expensive to recover the supply of expertise.
INNOVATION FOR SUPERCOMPUTING
. ~ . .
Innovation in supercomputing stems from application-motivated research that leads to
experimentation and prototyping, to advanced development and testbeds, and to deployment and
products. All the stages along that path need continuous, sustained investment in order that the needs of
the future will be met. If basic research activities are not supported, revolutionary advances are less
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4
THE FUTURE OF SUPERCOMPUTING: ANINTERIMREPORT
likely; if experimentation and advanced development are not done, the promising approaches never ripen
into products.
In supercomputing, innovation is important in architecture, in software, in algorithms, and in
application strategies and solution methods. The coupling of these aspects is equally important.
Major architecture challenges stem from the uneven performance scaling of different components. In
particular, as the gap between processor speeds, memory bandwidth, and memory and network latency
increases, new ideas are needed to increase bandwidth and hide (tolerate) latency. Additionally, as new
mechanisms are introduced to address those issues, there is a need for ways to supply a stable software
interface that facilitates exploiting hardware performance improvements while hiding the changes in
.
mecnamsm.
The need for software innovation is motivated by its role as an intermediary between the application
(the problem being addressed) and the architectural platform. Innovation is needed in the ways that
system software manages the use of hardware resources, such as network communication. New
approaches are needed for ways in which the applications programmer can express parallelism at a level
high enough to reflect the application solution and without platform-specific details. Novel tools are
needed to help application-level software designers reason about their solutions at a more abstract and
problem-specif~c level. Software technology is also needed to lessen future dependence on legacy codes.
Enough must be invested in the creation of advanced too! and environment support for new language
approaches so that users can more readily adopt new software technology. Importantly, advances in
algorithms can sometimes improve performance much more than architectural and software advances do.
More realistic simulations and modeling require not only increased supercomputer performance but
also new methods to handle finer spatial resolution, larger time scales, and very large amounts of
observational or experimental data. Additional applications challenges for which innovation is needed are
the coupling of multiple physical systems, such as the ocean and the atmosphere, and the synthesizing of
a physical system's design by analytic estimation of its properties. Emerging applications in areas such as
bioinformatics, biological modeling, and nanoscience and technology are providing both new
opportunities and new challenges.
THE ROLE OF THE GOVERNMENT
There are several important arguments for government involvement in the advancement of
supercomputers and their applications. The first is that unique supercomputing technologies are needed
to perform essential government missions and to ensure that critical national security requirements are
met. Furthermore, without the government's involvement, market forces are unlikely to drive sufficient
innovation in supercomputing, because the innovators like innovators in many other high-technology
areas do not capture the full value of their innovations. Historically, it seems that innovations in
supercomputing have played an important role in the evolution of today's mainstream computers and
have provided important benefits by virtue of their use in science and engineering. These benefits seem
to significantly exceed the value captured by the initial inventors.
It appears that the ability of government to affect the supercomputing industry has diminished
because supercomputing is a smaller fraction of the total computer market and computer technology is
increasingly a commodity. This situation requires a careful assessment of the most effective ways for
government to influence the future of supercomputing.
Representative terms from entire chapter:
evolve current
