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          ADVANCED COMPUTER ARCHITECTURE LABORATORY SEMINAR

       Cooperative Shared Memory and the Wisconsin Wind Tunnel

		  Mark Hill, James Larus, David Wood
		     Computer Sciences Department
		   University of Wisconsin--Madison
			  1210 W. Dayton St.
			Madison, WI 53706  USA


This talk describes two new ideas: Cooperative Shared Memory, a new
approach to building large-scale, shared-memory parallel computers,
and Virtual Prototyping, a new methodology for rapidly prototyping
parallel computers.

Cooperative shared memory combines a parallel programming model with
simple hardware.  The model informs programmers of the cost of
operations and tells hardware designers which cases are common.  Our
initial implementation uses a simple model, called Check-In/Check-Out
(CICO), and even simpler hardware called Dir[1]SW.  In CICO, programs
bracket uses of shared data with a {\em check-out\/} annotation
marking the expected first use and a {\em check-in\/} annotation
terminating the expected use of the data.  Dir[1]SW is a minimal
directory protocol that adds little complexity to message-passing
hardware, but efficiently supports programs written within the CICO
model.

Virtual prototyping is a new technique that allows rapid prototyping
of parallel computers.  Virtual prototyping uses a host computer and a
software layer to mimic a target machine and record performance
metrics.  The host directly executes most target operations.  The
Wisconsin Wind Tunnel (WWT) is a virtual prototype of CICO/Dir[1]SW
that runs on a Thinking Machines CM-5.  It uses shared virtual memory
together with ECC (error-correcting code) bits to invoke the virtual
prototype trap handlers on target cache misses.

Preliminary measurements show that the CICO programming model is
effective and that a virtual prototype can be quickly built and
executes large application programs at hardware speeds.



TIME:	1:00 PM, Thursday, 14 January 1993
PLACE:	EEB 248, USC University Park Campus
HOST:	Prof. Alvin M. Despain, (213) 740-6006


NOTE:	Prof. Hill will have time for individual or group meetings
after about 3:00 PM.  To schedule an appointment, please contact Ms.
Susan Moore, (213) 740-4462, susanm@usc.edu.