John Hennessy and David Patterson Impact Statement
Additional Notes Supporting Nomination by Forest Baskett and Krishna Palem
The synergy between compiler optimizations and computer architectures has been the key to driving innovation in
computer science at the highest level. For the most part, the focus and impact had been on achieving performance,
interpreted to be the speed of execution of applications, and on the ease of developing them—the latter concern
sometimes referred to as (programmer) productivity. Keeping these twin goals in mind, the Stanford MIPS project
and its commercial instantiations have galvanized the field of modern computer architecture Starting with the first
public disclosure of the MIPS architecture in 1981 by a group led by John Hennessy[1], and the Berkeley RISC
architecture, similarly led by David Patterson[2]. As early as 1994 and 1997 respectively, the tremendous impact of
these two seminal efforts could be easily discerned through their commercial instantiations, respectively the SUNSparc and MIPS products, as shown in Figure 1 (a) and (b); Berkeley inspired SPARC was used by 34% of the
workstations deployed by 1994, whereas MIPS represented 26.7% of the total embedded systems market by 1997.
Figure 1: The early impact of the MIPS and Berkeley RISC projects
It is striking to note that in addition to the direct impact of the commercial instantiations of these two efforts—the
SPARC and MIPS products—Advanced RISC Machines or ARM was also heavily influenced by these two designs.
To understand this, we quote from ARM Inc.’s history cite where they note ``For example, Sun developed the
SPARC RISC chip and architecture for its own computer workstations, while notable RISC processors from
established chip producers include Intel's i860 graphics processor and AMD's 29000, which has mainly been used as
a graphics accelerator or in printers. However, both Sun's and MIPS' efforts were based on earlier research efforts at
Stanford and Berkeley universities respectively, while Acorn's project was effectively begun from scratch, although
reports on the Berkeley and Stanford research were read by the Acorn team and were part of the inspiration behind
designing a RISC processor.’’ By 2009, as shown in Figure 2, MIPS and ARM had 41% of the overall
microprocessor market, and with a cumulative sales of over 16.6 billion processors by 2010!
Figure 2: The impact of the MIPS and ARM processors
1.
In the Beginning
By the late 1970s, ambitious processor architectures were being developed at significant cost, whereas it was
proving rather hard to truly exploit their complexity while retaining a level of productivity. This motivated John
Cocke and a team of researchers at IBM to take a deeper look at the value of implementing processor architectures
with ever increasing complexity. The resulting project 801 [3], many credit, as having established the importance of
a simple instruction set and the utility of a compiler in being able to exploit it. The projects at Berkeley and Stanford
(Figure 2) succeeded in indelibly establishing the influence of this principle in modern computer architecture as we
know it. We have already seen that the commercial derivatives of this processor had significant a impact in terms of
sheer numbers, on modern microprocessors. However, a subtler event which turned out to be epochal in
promulgating this philosophy, was the textbook authored by the protagonists of these projects, Hennessy and
Patterson. This book added significant momentum to a technical avalanche that was already on the way within the
industrial realm—various RISC processors were designed at that time including the DEC ALPHA and the SUN
SPARC architectures—by creating a pedagogically well-founded, cohesive, and quantitative framework through
which architectures could be viewed, rigorously evaluated, and ultimately innovated. A central concept that enabled
this was the approach of elevating the concept of an instruction set architecture (ISA) to be an abstraction worthy of
independent consideration in specification, analysis and evaluation in its own right, decoupled from the particular
manner in which it might (or might not) be implemented—the latter being an issue that became localized to the more
detailed world of microarchitecture. In our view, the book succeeded in giving computer architecture a lucid and
elegant framework that was methodologically reductionist—one does not always associate it with, nor is it always
tractable to achieve this in an area where detailed engineering considerations are intimately intertwined with
conceptual considerations.
J. Cocke
IBM-801
Project [3]
MIPS Computer
Systems was
founded
J. Hennessey
and D. Patterson
“Computer
architecture: a
quantitative
approach” [8]
Over 48 million
MIPS
architecture
based
processors sold
Source: MIPS
Corporation
1981
1980
J. Hennessey
MIPS project [1]
SPARC
developed by
Sun
Microsystems
Source: Netrino – The
Embedded Systems Expert
1987
1984
D. Patterson
RISC Project
[2]
Embedded
processors occupy
98% of the total
processor market
and represents 8.8
billion units
1990
1997
Advanced
RISC
Machines
(ARM) Ltd.
was founded
Less than 10 million
units based on ARM
architecture shipped
Source: Arm Holdings plc
2005
2010
A cumulative of 16.6
billion MIPS and
ARM based
processors shipped
Source:MIPS Corporation &
Arm Holdings plc
Figure 3. The major events and the impact of Hennessy and Patterson in the microprocessor arena
Thus, while the IBM 801 project started shifting the ``balance of power’’ from a hardware based microarchitecture,
to software based compiler-centric technique, this was motivated by traditional concerns of achieving high
performance. The efforts led by Hennessy and Patterson provided several crucial pivots beyond goal of the IBM 801
project, which was to demonstrate the importance of a compiler-centric approach to achieving high-performance and
were motivated by concerns that proved significant to the eventual impact of processors with simple instruction sets.
First, they wanted to overcome the burdens and overheads of having extra layers of microprogramming which made
the interpretations of instructions by hardware engines both cumbersome and inefficient. The result was a focus on
simplicity and efficiency. This in turn allowed the use and exploitation of (the then emerging) VLSI technology in a
variety of ways. The incorporation of instruction level parallelism, and an emphasis on using the increasingly
available silicon for on-chip caches, are two examples of this trend—in contrast, the IBM 801 was a wire-wrapped
board with composed of Motorola 10K parts built out of emitter coupled logic. Of course, the efficiency factor has
turned out to be very important in the embedded market as denoted by the dominance of the MIPS and ARM
2.
Beyond Microprocessors
Notably, in the 1980s, industry leaders Joseph (Josh) Fisher[4] and B. Ramakrishna (Bob) Rau [5] used the principle
that RISC enabled—that of a compiler managing hardware resources through architectural features and the concept
of a simple ISA—very successfully in the context of VLIW systems, at the heart of most if not all modern DSP
processing. To understand the significance of DSP processing, we note that (Figure 4) the total revenue associated
with the DSP market was close to all of the microprocessor related revenue from Intel.
Figure 4. Comparing the revenue associated with DSP processors with that of Intel from microprocessors.
On a personal note, this lesson also crucially influenced the work of one of the c-nominators. To elaborate, by 1999,
it was apparent that for customized embedded platforms to proliferate, it was essential to include malleable or
reconfigurable hardware into the mix, thereby adding a new dimension along which NRE and time-to-market had to
be combated. To tackle this challenge, Palem adopted the conceptual view and philosophy underlying the original
RISC lessons in a commercial effort pursued through Proceler Inc [6]—that of using an optimizing compiler and
``assemble’’ customized processors on reconfigurable hardware substrates quickly, and at low cost. This resulted in
the widely-used technology of Dynamically Variable Instruction Set Architectures (DVAITA),—the basis for
product offerings from major manufacturers of reconfigurable systems and their tools including Xilinx, Altera and
Symplicity and elucidated by Max Baron, its editor-in-chief, in the industry bellwether Microprocessor Report as a
nominee for one of the four outstanding technologies of 2002 [7]. In this connection, Max Baron noted that “It's no
longer possible to assume you can design a processor without having a good idea of the system architecture in
which it will be used and the workload it will execute....some of TI and ADI's DSP chips proves that processors are
designed with specific applications in mind....Proceler takes a different route: it can call "soft" hardware into
existence to accelerate parts of a workload that require high performance. Altera, Xilinx, Triscend, and others
provide microprocessor cores and raw hardware that can be programmed at boot time, or, if time permits, at run
time.”
References
[1] J. L. Hennessy, N. Jouppi, F. Baskett, and J. Gill, MIPS: a VLSI processor architecture. Technical Report CSL-TR-81-223,
Stanford, CA, USA, 1981.
[2] D. A. Patterson and C. H. Sequin, RISC I: A reduced instruction set VLSI computer, in the Proceedings of the International
Symposium on Computer Architecture, pages 443-458, 1981.
[3] G. Radin. The 801 minicomputer. IBM Journal of Research and Development, 27(3):237-246, 1983.
[4] J. A. Fisher, Trace scheduling: A technique for global microcode compaction, in the IEEE Transactions on Computers,
30(7):478-490, 1981.
[5] B. R. Rau, C. D. Glaeser, and E. M. Greenawalt, Architectural support for the efficient generation of code for horizontal
architectures, in the Proceedings of the Symposium on Architectural Support for Programming Languages and Operating
Systems, pages 96-99, 1982.
[6] K. Palem, H. Patel, and S. Yalamanchili. An instruction set architecture to aid code generation for hardware platforms having
multiple heterogeneous functional units, 2000. US Patent, Publication No. WO/2002/041104.
[7] M. Baron, Technology 2001: On a clear day you can see forever, Microprocessor Report, February 2002.
[8] J. L. Hennessy and D. A. Patterson. Computer architecture: a quantitative approach. Morgan Kaufmann Publishers Inc., San
Francisco, CA, USA, 1990.