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February 14, 2000, Issue: 1100
Section: News
ADVANCED PROCESSORS Intel, IBM, Compaq, Sun take
devices to the higher level at conference -- Four drive MPUs
into gigahertz performance
Chris Edwards and Will Wade
SAN FRANCISCO - Like multiple players setting a new standard for home
runs, four microprocessors flashed past the gigahertz performance mark at last
week's International Solid-State Circuits Conference here.
Intel, IBM, Compaq and Sun brought gigahertz processors to the stage at the
47th ISSCC.
Advanced Micro Devices Inc. privately showed an Athlon processor, based
on copper interconnect and produced at AMD's new fab in Dresden,
Germany, running at 1 GHz.
Meanwhile, an evening panel concluded that microprocessors are on course
for another hundredfold increase in performance over the next decade.
Intel Corp. delivered a gigahertz Coppermine MPU that still uses all-aluminum
interconnect. Design manager Peter Green said the device has an on-die Level
2 cache that runs at the same frequency as the processor core. Green said the
1-GHz Coppermine will be available commercially before year's end. "This is
not a stunt," he said. "A gigahertz design brings tangible performance increases
to the user. You can see it and feel it."
Not to be outdone, the design team at Sun Microsystems Inc. went to some
lengths to explain why they deserved entry to the gigahertz club. The
UltraSparc-III, described in the ISSCC's advance program as a 600-MHz
design and in the ISSCC paper itself as running at 800 MHz, actually has
been pushed to a gigahertz in the laboratory, the company said. However,
Sun's testers have not been able to fully verify its performance and voltage at
that speed.
"Unfortunately, 800 MHz is where our testers maxed out," said Ray Heald, a
distinguished engineer at Sun. "So, we don't have the full shmoo plot to show."
Still, said Sun senior engineer Dale Greenley, "We now have
production-quality chips running at 1 GHz. Our frequencies are higher than
expected."
The chip is expected to be used in parallel-processing machines packing as
many as 1,000 processors apiece. It has a dedicated multiprocessor bus to
maintain cache coherency as well as a memory bus. New caches, such as a
2-kbyte prefetch cache and a 2-kbyte write cache, were added in an attempt
to iron out differences between the processor's clock speed and the much
slower external memory.
"Moving data on and off the chip is becoming increasingly difficult," said
Greenley. "People are working on 1-GHz processors but memory bandwidth
is not scaling as quickly. We spent a long time developing the on-chip memory
architecture."
The UltraSparc-III designers opted for an approach that split the register file
in two. One part contains the 32 working registers, with a full complement of
read and write ports. Another 160 registers have just three write ports, used
for writing to memory at times of a window overflow. A dedicated transfer
port between the two sets of registers is used to transfer the entire contents
from a stored window to the working set in one cycle.
For its part, IBM Corp. showed a 64-bit PowerPC design that coaxed
gigahertz performance out of a very short pipeline.
"Most of the complexity in microprocessors today comes from the problems
of having very long pipelines to generate high frequencies," said Keith
Diefendorff, editor-in-chief of the Microprocessor Report. "A short pipeline is
more efficient."
The IBM team used a four-stage design, along with copper interconnect and a
0.22-micron process. "Traditionally, one of the ways to improve performance
in a processor is to add pipeline stages, so the amount of work done per cycle
goes down," said Peter Hofstee, from the IBM research lab in Austin, Texas.
"We have improved cycle time by requiring harder work in all pipeline stages,
so this design is well-balanced."
The chip delivers peak performance of 1.2 GHz, but at the cost of driving the
operating temperature up to 125 degrees C. Diefendorff termed the IBM
design more research experiment than production-bound device, and said it is
not likely to see any commercial applications.
The final entry in the gigahertz game was an Alpha chip from Compaq
Computer Corp.'s Alpha Processor Inc. subsidiary. Built with seven layers of
aluminum interconnect, an 0.18-micron process and low-k dielectric material,
the device is designed for both standard wire-bond and flip-chip packaging.
Bradley Benschneider, senior member of the technical staff at Compaq, said
that performance will increase as much as 10 percent with the use of flip-chip
packaging. The pro-cessor ran at 1.65 volts.
Editor Diefendorff said the Alpha architecture has always been know for
speed, but has achieved very little market presence. Compaq is the only
significant OEM to use Alpha chips in its servers, and Diefendorff predicted
that even the Houston PC maker would switch to Intel chips once its 64-bit
processors become available later this year. "I can't imagine that Compaq will
continue to carry the [Alpha] architecture forward," he said.
"There is nothing magic about running at 1 GHz," added Diefendorff, formerly
a microprocessor design manager at Motorola and AMD. "It is certainly a
goal that people have been striving for, but running at 1 GHz is no different
from running at 999 MHz. There are plenty of applications that use all the
horsepower you can throw at them," he said. "With more power, we won't
necessarily see new and revolutionary applications, but we might start to see
some that work right."
How long, how fast?
Architectural techniques such as multithreading will be widely used to boost
microprocessor performance even further-up to a hundredfold by 2010, said
participants at the panel session contemplating the future of the
microprocessor. While there are still gains to be had from frequency increases,
opinions dif-fered widely on how much. Fred Weber, vice president of AMD,
said, "It looks like there is another 10X to be had, but we can't take as many
gate delays out as we have over the last 10 years."
Hiroshi Iwai, a professor at the University of Tokyo, said the next 10 years
will see slower performance growth, following recent rapid increases in
frequency. By decade's end, current consumption for a high-end processor
will have reached 290 amps, he said.
"Beyond 2010, we will reach a kind of saturation point, not only in frequency
but in chip size," said Iwai.
"I'm a little less optimistic about frequency scaling," said Stanford University
professor Bill Dally. "I think 3X is possible. We are now at the point where it's
a lot more painful to squeeze a lot more out of clock cycles."
Intel fellow Fred Pollack reckoned that frequency could still be increased but
that process shrinks would become less important. "We'll still get good
performance out of process technologies but not as much," Pollack said. "We
will get more out of clever circuit techniques rather than process."
He called power the big problem. "We are already past the point where the
power density is higher than that of a hot plate," said Pollack. "We are
reaching the point where it is that of a nuclear reactor, although the chips are a
lot smaller."
CHRIS EDWARDS IS THE EDITOR OF EMBEDDED SYSTEMS, A
U.K.-BASED SISTER PUBLICATION TO EE TIMES.
eetimes.com
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