Supercomputer
"A supercomputer is a device for turning compute-bound problems into
I/O-bound problems."
--Seymour Cray (widely attributed; possibly apocryphal)
A supercomputer is a computer that leads the world in terms of processing
capacity, particularly speed of calculation, at the time of its
introduction. The first supercomputers were introduced in the 1960s, led
primarily by Seymour Cray at Control Data Corporation (CDC), which led the
market into the 1970s until Cray split off to form his own company, Cray
Research, and then took over the market. In the 1980s a large number of
smaller first entered the market, a parallel to the creation of the
minicomputer market a decade earlier, many of whom disappeared in the
mid-1990s "supercomputer market crash". Today supercomputers are typically
one-off custom designs produced by "traditional" companies such as IBM and
HP, who had purchased many of the 1980s companies to gain their experience.
The term Supercomputer itself is rather fluid, and today's supercomputer
tends to become tomorrow's also-ran, as can be seen from the world's first
(non solid state) computer Colossus, used to break German ciphers in World
War II. CDC's early machines were simply single very fast processors, some
ten times the speed of the fastest machines offered by other companies. In
the 1970s most supercomputers were dedicated to running a vector processor,
and many of the newer players developed their own such processors at lower
price points to enter the market. In the later 1980s and 1990s, attention
turned from vector processors to massive parallel processing systems with
thousands of simple custom CPUs. Today the parallel design is the only
remaining architecture, but based on "off the shelf" RISC microprocessors
such as the PowerPC or PA-RISC.
Software Tools
Software tools for distributed processing such as MPI and PVM and
proprietary solutions such as Beowulf and MOSIX facilitate the creation of a
sort of "virtual supercomputer" from a collection of ordinary workstations
or servers. Technology like Rendezvous pave the way for the creation of ad
hoc computer clusters. An example of this is the distributed rendering
function in Apple's Shake compositing application. Computers running the
Shake software merely need to be in proximity to each other, in networking
terms, to automatically discover and use each other's resources. While no
one has yet built an ad hoc computer cluster that rivals even yesteryear's
supercomputers, the line between desktop, or even laptop, and supercomputer
is beginning to blur.
Uses
Supercomputers are used for highly calculation-intensive tasks such as
weather forecasting, climate research (including research into global
warming), molecular modeling (computing the structures and properties of
chemical compounds, biological macromolecules, polymers, and crystals),
physical simulations (such as simulation of airplanes in wind tunnels,
simulation of the detonation of nuclear weapons, and research into nuclear
fusion), cryptanalysis, and the like. Military and scientific agencies are
heavy users.
Design
Supercomputers tradionally gained their speed over conventional computers
through the use of innovative designs that allow them to perform many tasks
in parallel, as well as complex detail engineering. They tend to be
specialised for certain types of computation, usually numerical
calculations, and perform poorly at more general computing tasks. Their
memory hierarchy is very carefully designed to ensure the processor is kept
fed with data and instructions at all times—in fact, much of the
performance difference between slower computers and supercomputers is due to
the memory hierarchy design and componentry. Their I/O systems tend to be
designed to support high bandwidth, with latency less of an issue, because
supercomputers are not used for transaction processing.
As with all highly parallel systems, Amdahl's law applies, and supercomputer
designs devote great effort to eliminating software serialization, and using
hardware to accelerate the remaining bottlenecks.
Supercomputer challenges and technologies
* A supercomputer generates heat and must be cooled. Cooling a
supercomputer is a major HVAC problem.
* Information cannot move faster than the speed of light between two
parts of a supercomputer. For this reason, a supercomputer that is many
meters across must have latencies between its components measured at
least in the tens of nanoseconds. Seymour Cray's Cray supercomputer
designs attempted to keep cable runs as short as possible for this
reason.
* Supercomputers consume and produce massive amounts of data in a very
short period of time. Much work is needed to ensure that this
information can be transferred quickly and stored.
Technologies developed for supercomputers include:
* Vector processing
* Liquid cooling
* NUMA
* Striped disks (the first instance of what was later called RAID)
* parallel filesystems
Processing Techniques
Vector processing techniques were first developed for supercomputers and
continue to be used in specialist high-performance applications. Vector
processing techniques have trickled down to the mass market in DSP
architectures and SIMD processing instructions for general-purpose
computers.
Operating Systems
Their operating systems, often variants of UNIX, tend not to be as
sophisticated as those for smaller machines, since supercomputers are
typically dedicated to one task at a time rather than the multitude of
simultaneous jobs that makes up the workload of smaller devices.
Programming
The parallel architectures of supercomputers often dictate the use of
special programming techniques to exploit their speed. Special-purpose
FORTRAN compilers can often generate faster code than the C or C++
compilers, so FORTRAN remains the language of choice for scientific
programming, and hence for most programs run on supercomputers. To exploit
the parallelism of supercomputers, programming environments such as PVM and
MPI for loosely connected clusters and OpenMP for tightly coordinated shared
memory machines are being used.
Types of general-purpose supercomputers
There are three main classes of general-purpose supercomputers:
* Vector processing machines allow the same (arithmetical) operation to
be carried out on a large amount of data simultaneously.
* Tightly connected cluster computers use specially developed
interconnects to have many processors and their memory communicate with
each other, typically in a NUMA architecture. Processors and networking
componenets are engineered from the ground up for the supercomputer.
The fastest general-purpose supercomputers in the world today use this
technology.
* Commodity clusters use a large number of commodity PCs, interconnected
by high-bandwidth low-latency local area networks.
As of 2002, Moore's Law and economies of scale are the dominant factors in
supercomputer design: a single modern desktop PC is now more powerful than a
15-year old supercomputer, and at least some of the design tricks that
allowed past supercomputers to out-perform contemporary desktop machines
have now been incorporated into commodity PC's. Furthermore, the costs of
chip development and production make it uneconomical to design custom chips
for a small run and favor mass-produced chips that have enough demand to
recoup the cost of production.
Additionally, many problems carried out by supercomputers are particularly
suitable for parallelization (in essence, splitting up into smaller parts to
be worked on simultaneously) and, particularly, fairly coarse-grained
parallelization that limits the amount of information that needs to be
transferred between independent processing units. For this reason,
traditional supercomputers can be replaced, for many applications, by
"clusters" of computers of standard design which can be programmed to act as
one large computer. Many of these use the Linux operating system; they are
then called Beowulf clusters.
As of 2003, the world's number 3 ranked supercomputer is a commodity cluster
running Linux on Intel x86 hardware. However, a number of new commodity
cluster projects that will run Linux on thousands of AMD x86-64 CPUs are
expected to run at even higher speeds. If these trends continue, the Linux
operating system is likely to become the de facto standard supercomputer
operating system.
Special-purpose supercomputers
Special-purpose supercomputers are high-performance computing devices with a
hardware architecture dedicated to a single problem. This allows the use of
specially programmed FPGA chips or even custom VLSI chips, allowing higher
price/performance ratios by sacrificing generality. They are used for
applications such as astrophysics computation and brute-force codebreaking.
Examples of special-purpose supercomputers:
* Deep Blue, for playing chess
* Configurable computing
* GRAPE for astrophysics
The fastest supercomputers today
The speed of a supercomputer is generally measured in FLOPS (floating point
operations per second); this measurement ignores communication overheads and
assumes that all processors of the machine are provided with data and are
working at full speed.
As of early 2002, the fastest supercomputer is the Earth Simulator at the
Yokohama Institute for Earth Sciences. It is a cluster of 640
custom-designed 8-processor vector processor computers based on the NEC SX-6
architecture (a total of 5120 processors). It uses a customised version of
the UNIX operating system.
Its performance is over 5 times that of the previous fastest supercomputer,
the cluster computer ASCI White at Lawrence Livermore National Laboratory.
The United States Government ASCI initiative aims to replace nuclear testing
with simulation, to maintain its strategic advantage in the presence of
nuclear test-ban treaties.
PARAM is another series of supercomputers.
Timeline of supercomputers
Period Supercomputer Speed Location
1943-1944Colossus Ê Bletchley Park, England
1945-1950Manchester Mark I Ê University of Manchester,
England
1950-1955MIT Whirlwind Ê Massachusetts Institute of
Technology, Cambridge, MA
1955-1960IBM 7090 210 KFLOPS U.S. Air Force BMEWS (RADC),
Rome, NY
1960-1965CDC 6600 10.24 Lawrence Livermore
MFLOPS Laboratory, California
1965-1970CDC 7600 37.27 Lawrence Livermore
MFLOPS Laboratory, California
1970-1975CDC Cyber 76 Ê Ê
1975-1980Cray-1 160 MFLOPS Los Alamos National
Laboratory, New Mexico (1976)
1980-1985Cray X-MP 500 MFLOPS Los Alamos National
Laboratory, New Mexico
1985-1990Cray Y-MP 1.3 GFLOPS Los Alamos National
Laboratory, New Mexico
1990-1995Fujitsu Numerical Wind 236 GFLOPS National Aerospace Lab
Tunnel
1995-2000Intel ASCI Red 2150 Sandia National Laboratories,
GFLOPS New Mexico
2000-2002IBM ASCI White, SP 7226 Lawrence Livermore
Power3 375 MHz GFLOPS Laboratory, California
2002- Earth Simulator 35 TFLOPS Yokohama Institute for Earth
Sciences, Japan
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