A Technical History of the SEI

Software for Heterogeneous Machines
The Challenge: Meeting Performance Goals for Real-Time Applications
Involving Heterogeneous Machines
Around the time that the SEI was formed, DARPA was sponsoring research, under the Strategic
Computing Initiative, in a number of computation-intensive, real-time applications, such as autonomous
land vehicles. These applications required processing data obtained from sensors (for example,
TV cameras, radar, and sonar), extracting basic features of the terrain, consulting low-level
knowledge sources to build hypotheses about paths and obstacles, and consulting higher level
knowledge sources to make decisions about current vehicle location, desired target location, and
ways to arrive there.
Given the computer technology of the day, the demands for computing cycles were so great that
conventional processors could not meet all the performance goals. Certain tasks in the applications
required special-purpose processors capable of executing some tasks very quickly—but such
processors were perhaps not very useful for other tasks.
A Solution: Software for Heterogeneous Machines (Durra)
Recognizing this future need to support applications running on networks of these special-purpose
processors executing concurrent tasks, the SEI initiated research in software for heterogeneous
machines. This work continued from 1985 through 1992. The heterogeneous machines targeted
by this research consisted of general-purpose processors, special-purpose processors, memory
boxes, and switches that could be configured in arbitrary logical networks. The application tasks
were independent, large-grained, concurrent programs, written in various programming languages
and communicating via message passing protocols. Heterogeneous machines, such as the one assumed
in this research, pushed the leading edge of software engineering [Barbacci 1988].
By 1991, the research focused on improving the practice of developing and maintaining distributed
systems. The SEI had developed a language and methodology (Durra) 9 for implementing distributed,
real-time applications on heterogeneous computer systems [Barbacci 1986a, 1997, 1987;
Doubleday 1992]. The SEI also developed a runtime environment to support distributed applications
that use heterogeneous machines [Weinstock 1989].
This research improved the state of the practice of software engineering by integrating techniques
for specifying the software structure of applications, specifying reusable component programs,
and specifying the timing and functional behavior of component programs and applications [Barbacci
1986b].
Much of the research was done in collaboration with the CMU Department of Computer Science
(now part of the School of Computer Science), building on and leveraging its work on Nectar [Arnould
1989], a prototype heterogeneous machine that was also funded by DARPA to develop applications
for an autonomous land vehicle.
9 The name Durra is not an acronym. Rather it came from Sorghum bicolor, commonly called sorghum
and also known as durra, jowari, or mil—a grass species cultivated for its edible grain. Since
the project was dealing with large-grained parallelism, the name seemed appropriate.
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