Virginia Polytechnic Institute and State University

Cost-Conscious Supercomputing

The Architecture

The Power Mac G5: A New Era in Supercomputing

Virginia Tech had already built a number of high-powered clusters, although nothing of this scale. Then, when the Power Mac G5 was introduced in June 2003 — boasting dual 2 GHz G5 processors and up to 8GB of main system memory — the landscape of supercomputing had changed for the better. It wasn’t long before Virginia Tech had done the math: The Power Mac G5 provided greater price-performance than any other system on the market.

“I realized that the PowerPC 970 processor would be ideal for us. Its fused multiply-add operation gives it a floating-point performance equal to — if not better than — Intel’s Itanium2 solution.”

— Dr. Srinidhi Varadarajan

“We already had discussions in progress with another hardware provider,” recalls Lockhart. “But obviously the IBM PowerPC 970 processor, with its supercomputing pedigree, was really appealing to us. We’d been tracking the ‘buzz’ for several months, and we were very anxious to see if the Power Mac G5 would give us another platform option. When we heard the announcement in June, we basically wrapped up our other discussions and went down the new path with Apple.”

Record-Breaking Processing Speed

Lockhart says several features of the new Power Mac G5 computers were especially attractive for Virginia Tech. “AMD’s Opteron can only execute two double-precision floating-point instructions per clock cycle, which kind of limits system performance,” he notes. The G5 processor has two floating-point units. Thus, unlike the Opteron, it can perform fused multiply-adds, giving four operations per clock cycle and achieving a theoretical limit of 8 gigaflops from a 2 GHz processor. All this is in addition to the G5 processor’s Velocity Engine floating point and integer units.

Says Lockhart, “We would have had to buy more nodes to equal the amount of performance needed to hit our ten-teraflop goal. But the hypertransport memory architecture of the new Macs gives us lots of [speed]. And, having the PCI-X bus in the system gives us the bandwidth we need for our communications fabric.”

Adds Varadarajan, “When we were evaluating machines and platforms, I realized that the PowerPC 970 processor would be ideal for us. Its fused multiply-add operation gives it a floating-point performance equal to — if not better than — Intel’s Itanium2 solution. Pretty quickly, I knew that the Power Mac G5 machines would help us reach the goals we had in mind for our supercomputer.”

The PowerPC G5 gets its smarts from the execution core of IBM’s 64-bit POWER4 processor — recipient of Microprocessor Report’s 2001 Analyst’s Choice Award for Best Workstation/Server Processor. Apple collaborated with IBM to leverage this industry-leading design for the Power Mac G5, combining an optimized Velocity Engine with a new superscalar, superpipelined execution core that supports more than 200 simultaneous in-flight instructions.

For more information on the G5 processor, visit Apple’s G5 processor page.

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