Spain’s Museo de Historia de la Computación has unveiled a full-size visual replica of the Cray-1 supercomputer, which appeared in 1976, but this time the model is powered by 30 used Mac Minis, most of them dating from 2012. The project took 18 months to complete and aims to commemorate both the 50th anniversary of the Cray-1 and the founding of Apple.
The project’s value is not limited to its exterior appearance; the team connected the devices into a computing cluster containing 64 effective processing cores and achieved approximately 1.3 teraflops in its latest test using custom Python software for matrix multiplication. The project previously recorded 1.5 teraflops when running 70 cores, before one of the nodes stopped working. The cluster consists of five devices with quad-core Intel Core i7 processors and 25 devices with dual-core Core i5 processors, except for two units from 2014.
From Vector Processing to a Parallel Cluster
The original Cray-1 relied on vector processing, meaning that one instruction was executed on multiple data elements simultaneously, and its theoretical peak performance was approximately 160 megaflops. The new version instead distributes the workload among independent processors through a parallel cluster, enabling relatively old consumer devices to deliver performance far exceeding that of the research machine that inspired it.
The team chose macOS Mojave 10.14 instead of a traditional Linux distribution, taking advantage of its built-in support for the Message Passing Interface, or MPI, which allows tasks to be passed between cluster nodes. Museum visitors can watch matrix algorithms operate in real time, starting with a single core and progressing to the entire group running in parallel.
Silent Cooling Inside a Cray-1-Inspired Structure
The project faced the challenge of cooling 30 devices inside a single structure. To avoid the noise of server fans, the team mounted the Mac Minis vertically inside a steel structure, with aluminum trays for each device. This arrangement allows hot air to rise through the structure and exit through its upper openings, functioning as a natural thermal chimney without additional mechanical fans.
According to the museum, most of the noticeable noise comes from two gigabit Ethernet adapters at the base of the structure, at a level ranging from 30 to 33 decibels, with plans to replace them with two silent models. The noise from each device while idle measures between 12 and 15 decibels, according to the stated data, although no precise measurement of the noise from inside the completed exhibit is available.
What Changes in Practice?
The project offers a direct visual explanation of computing’s transformation over five decades: from a supercomputer designed specifically for research to a group of relatively outdated consumer devices. At the same time, it shows that higher theoretical performance does not eliminate the challenges of building a cluster, such as node management, data exchange, cooling, and the result’s dependence on the type of test used.
The team also designed a control station inspired by the DEC VT05 and Processor Technology Sol-20 terminals from the 1970s, incorporating a main Mac Mini to manage the remaining nodes. Flat Samsung displays were used instead of CRT screens to avoid connection problems between technologies from different eras. Future plans include adding 3.5- and 5.25-inch floppy disk drives, a 3D-printed keyboard structure, and original IBM System/3 lamps.
Expansion Plan Toward TOP500
The team plans to fill the empty second half of the tower through a crowdfunding campaign to purchase an additional 70 to 80 M4 Mac Minis, with the goal of creating a cluster capable of entering the TOP500 supercomputer list. This remains a future objective and is not a ranking the project has achieved at present.
The replica is on permanent display at the museum alongside two unused original Cray CX1 systems, while guided visits are available on Saturdays from 11:30 a.m. to 2 p.m.