The Power and Legacy of Virginia Tech's Mac-Based Supercomputers

When we think about data centers today, we often picture rows of GPU-packed racks run by companies like Microsoft, Google, Amazon, and Meta, and used by AI labs such as OpenAI and Anthropic. Much of that hardware does one of two jobs: training new models or running finished ones to answer requests from millions of people around the world. A supercomputer is built from many of the same parts but for a different purpose. It is typically owned by a government lab or university and designed for scientific simulation, such as modeling climate, nuclear physics, or new materials. That work demands high-precision math and very fast communication between processors. Rather than serving the masses, a supercomputer is shared among researchers, whose large jobs wait in a queue and run according to a schedule. Early examples like UNIVAC and the IBM 7030 were used by scientists working on atomic research. The Cray-1 came along in the mid-70s and accelerated such work to new levels. Each of these machines brought with it new technologies that made those breakthroughs possible. They were also fairly bespoke, built of components regular nerds could only dream about. Over time, that changed. By the time the 1990s rolled around, companies like Cray saw their hardware being outpaced by newcomers who were packing far more processors into their products. The kicker? Those processors were much more pedestrian than the custom silicon older supercomputers were built around. In 1998, David Bader built what he calls “the first bona fide Linux supercomputer” with off-the-shelf parts, including the Intel Pentium II. 1 That brings us to 2003, and the subject of today’s article: Virginia Tech’s Mac-based supercomputers. Bang for the Buck # As you can see from these photos , System X — pronounced “System Ten” 2 — was built with 1,100 Power Mac G5s: Photos from Virginia Tech’s Advanced Research Computing website, via the Wayback Machine . Honestly, I could end this article right here. Look how badass this all is! I really do love the look of the Power Mac G5. Virginia Tech built this supercomputer in the summer of 2003, with the goal of hitting 10 teraflops. Once it was up and running that fall, it ranked as the world’s third-fastest computer, and the fastest at an academic institution. You can see from this video that the G5 was chosen to hit these numbers without breaking the bank: (This video played as part of Apple’s product introduction for the Power Mac G5 itself.) The total cost was $5.2 million, 3 a far cry from the $400 million spent to build the fastest supercomputer at the time, the Earth Simulator . (System X also looked much cooler.) Both Virginia Tech faculty members and students could get time on the machine free of charge, and thanks to the dual 2.0 GHz processors inside each G5, their projects could tap into vast resources easily. On the software front, every node ran Mac OS X. The machines arrived running Mac OS X 10.2.7 , with plans to move to Panther shortly after. Each G5 came equipped with 4 GB of DDR400 RAM, a 160 GB Serial ATA hard drive, and a Mellanox InfiniBand PCI-X card, which allowed the machines to be linked to each other and to the network over high-speed cables. Notably, the Power Mac G5 didn’t support ECC memory. That would matter later. The G5s were unboxed and installed by students and faculty: The whole thing came together pretty quickly, according to this FAQ : Planning began in January of 2003. Facilities planning began in April of 2003. Renovations began the first week of August and were completed on September 23, 2003. Computers, network equipment, and cables began arriving the first week of September 2003. The computers arrived in six shipments during a seven day period and were processed into the racks in less than 2 hours per shipment with no more than 30 volunteers working a shift. Ethernet cabling (roughly 1200 connections) was done by a four man team from our internal communications and network services group and was completed in less than 14 days. InfiniBand cabling (roughly 1700 connections) began September 13, 2003 and was completed by a team of five people in 10 days. I was lucky to get an email about this from Sam Davies, who was a student and an Apple Campus Representative at Virginia Tech at the time. He told me: In the summer of 2003, I was fortunate to be a part of the team working to put System X together (that was the official name, unofficially the Mac community and everyone else called it “Big Mac”). The first 1,100 G5s off of Apple’s assembly line were unloaded from trucks, unboxed, and carried into server racks by a huge team of faculty, staff, Apple project folks, and student volunteers like me. Only one G5 tower in the batch of 1100 couldn’t be used, and that was because one of the Apple sales reps dropped it. (Those handles are sharp!) Of course, having a bunch of tower machines stuffed into racks isn’t very space-efficient. The next year, Apple had a solution. The Xserve G5 # Here’s Apple PR, in January 2004 : Apple today introduced Xserve G5, the most powerful Xserve yet, delivering over 30 gigaflops of processing power per system, about 60 percent more than the PowerPC G4-based Xserve. Xserve G5 features the same revolutionary PowerPC G5, 64-bit processor used in Virginia Tech’s cluster of Power Mac G5s—the world’s third fastest supercomputer. With unparalleled performance and manageability in a 1U rack-mount enclosure, Xserve G5 is the perfect server for today’s UNIX-based applications. Xserve G5 includes a new system controller with up to 8GB of PC3200 error correcting code (ECC) memory; three hot-plug Serial ATA drive modules that deliver up to 750GB of storage; optional internal hardware RAID; dual PCI-X slots, supporting 133 MHz PCI-X cards with over 1 GBps of throughput; and dual on-board Gigabit Ethernet for high-performance networking. The press release continues: “Xserve G5 delivers just what our customers have been asking for,” said Philip Schiller, Apple’s senior vice president of Worldwide Product Marketing. “With dual G5 processing power and up to 8GB of ECC memory, Xserve G5 is affordable, easy to manage and easy to cluster. Starting as low as $2,999, no one can offer better price performance in a 1U rack-mount design.” Available with either single or dual 2.0 GHz PowerPC G5 processors, the Xserve G5 architecture is based on an execution core that features massively parallel computation for an unprecedented 215 in-flight instructions, full symmetric multi-processing, two double precision floating-point units and an optimized Velocity Engine. Xserve G5 has the industry’s fastest front side processor bus—running at up to 1.0 GHz and delivering 8 GBps per processor. Building on the engineering feats first introduced in the Power Mac G5, Xserve G5 squeezes the incredible performance of dual PowerPC G5 processors into an ultra-thin 1U enclosure. An innovative copper heat sink design effectively removes heat from the processors while eight high-performance fans provide airflow for cooling the system. The fans are individually managed and monitored by a dedicated fan control processor; if a single fan fails the others speed up to compensate. The 1U enclosure has an array of over 30 sensors, including eight dedicated to temperature control, that continually monitor all critical system functions throughout the server. Tech tore down the Power Mac version of System X in January 2004 and rebuilt it with Xserve G5s that summer. ECC memory was a big part of the reason. As the school put it : “We needed to upgrade the system to something with error correcting code (ECC) RAM. The Power Macs did not support it and the XServes were coming.” The new array was made up of 1,100 dual 2.3 GHz Xserve G5 servers and six Xserve RAIDs. Those 2.3 GHz machines were custom-built by Apple for Virginia Tech; the public wouldn’t be able to buy one until Januar