The Connection Machines were a series of supercomputers that grew out of Danny Hillis's doctoral research at MIT in the early 1980s on alternatives to the traditional von Neumann architecture of computation. The Connection Machines (CMs), beginning with CM-1, were originally intended for applications in artificial intelligence and symbolic processing, but later versions found greater success in the field of computational science.
Origin of idea
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Danny Hillis and Sheryl Handler founded Thinking Machines (TMC) in Waltham, Massachusetts in 1983, moving in 1984 to Cambridge, MA. At TMC, Hillis assembled a team to develop what would become the CM-1 Connection Machine, a design for a massively parallel hypercubic arrangement of thousands of microprocessors, springing from this PhD thesis work at MIT in Electrical Engineering and Computer Science (1985). The dissertation won the ACM Distinguished Dissertation prize in 1985, and was presented as a monograph that overviewed the philosophy, architecture, and software for the first Connection Machine, including information on its data routing between CPU nodes, its memory handling, and the Lisp programming language applied in the parallel machine.
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Each CM-1 microprocessor has its own 4 kilobits of RAM, and the hypercubic array of them was designed to perform the same operation on multiple data points simultaneously, i.e., to execute tasks in single instruction, multiple data (SIMD) fashion. The CM-1, depending on the configuration, has as many as 65,536 individual processors, each extremely simple, processing one bit at a time. CM-1 and its successor CM-2 take the form of a cube 1.5 meters on a side, divided equally into eight smaller cubes. Each sub-cube contains 16 printed circuit boards and a main processor called a sequencer. Each printed circuit board contains 32 chips. Each chip contains a router, 16 processors, and 16 RAMs. The CM-1 as a whole has a 20-dimensional hypercubic routing network, a main RAM, and an input/output processor. Each router contains 5 buffers to store the data being transmitted when a clear channel isn't available. The engineers had originally calculated that 7 buffers per chip would be needed, but this made the chip slightly too large too build. Richard Feynman had previously calculated that 5 buffers would be enough, using differential equations involving the average number of bits, so they reduced the number of buffers to 5, and it worked fine. Each chip is connected to a switching device called a nexus. The CM-1 uses Feynman's algorithm for computing logarithms that he had developed at Los Alamos National Laboratory for the Manhattan Project. It is well suited to the CM-1, using as it did, only shifting and adding, with a small table shared by all the processors. Feynman also determined that the CM-1 would do QCD calculations faster than an expensive special purpose machine at Caltech. 
In order to improve its commercial viability, TMC launched the CM-2 in 1987, adding Weitek 3132 floating-point numeric co-processors and more RAM to the system. Thirty-two of the original one-bit processors shared each numeric processor. The CM-2 can be configured with up to 512 MB of RAM, and a RAID hard disk array, called a DataVault, of up to 25 GB. Two later variants of the CM-2 were also produced, the smaller CM-2a with either 4096 or 8192 single-bit processors, and the faster CM-200.
Due to its origins in AI research, the software for the CM-1/2/200 single-bit processor was influenced by the Lisp programming language and a version of Common Lisp, *Lisp (spoken: "Star-Lisp"), was implemented on the CM-1. Other early languages included Karl Sims' IK and Cliff Lasser's URDU. Much system utility software for the CM-1/2 was written in *Lisp. Many applications for the CM-2, however, were written in C*, a data-parallel superset of ANSI C.
With the CM-5, announced in 1991, TMC switched from the CM-2's hypercubic architecture of simple processors to an entirely new MIMD architecture based on a fat tree network of SPARC RISC processors. To make programming easier, it was made to simulate a SIMD design. The later CM-5E replaces the SPARC processors with faster SuperSPARCs. The CM-5 was the second-fastest system in the November 1993 TOP500 list, running 1024 cores with Rpeak of 131.0 GFlop/s.
Connection Machines were noted for their (intentionally) striking visual design. The CM-1 and CM-2 design teams were led by Tamiko Thiel. The physical form of the CM-1, CM-2, and CM-200 chassis was a cube-of-cubes, referencing the machine's internal 12-dimensional hypercube network, with the red LEDs, by default indicating the processor status, visible through the doors of each cube.
By default, when a processor is executing an instruction, its LED is on. In a SIMD program, the goal is to have as many processors as possible working the program at the same time – indicated by having all LEDs being steady on. Those unfamiliar with the use of the LEDs wanted to see the LEDs blink – or even spell out messages to visitors. The result is that finished programs often have superfluous operations to blink the LEDs.
References in popular culture
- Brewster Kahle - Lead engineer on the Connection Machine projects.
- David E. Shaw's NON-VON machine, which preceded the Connection machine slightly.
- FROSTBURG — a CM-5 used by the NSA
- Goodyear MPP
- ICL DAP
- Parallel computing
- W. Danny Hillis (1986). The Connection Machine. MIT Press. ISBN 0262081571.
- "William Daniel Hillis - Award Winner". ACM Awards. Retrieved 30 April 2015.
- Brewster Kahle & W. Daniel Hillis, 1989, The Connection Machine Model CM-1 Architecture (Technical report), Cambridge, MA:Thinking Machines Corp., 7 pp., see , accessed 25 April 2015.
- Richard Feynman and The Connection Machine, Physics Today, January 15, 1989
- "NOVEMBER 1993". www.top500.org. Retrieved 16 January 2015.
- Design Issues, (Vol. 10, No. 1, Spring 1994) ISSN 0747-9360 MIT Press, Cambridge, MA.
- Thiel, Tamiko (Spring 1994). "The Design of the Connection Machine". Design Issues. 10 (1). Retrieved 16 January 2015.
- "Bloodless Beige Boxes: The Story of an Artist and a Thinking Machine". IT History Society. 2 September 2014. Retrieved 16 January 2015.
- Hillis, D. 1982 "New Computer Architectures and Their Relationship to Physics or Why CS is No Good", Int J. Theoretical Physics 21 (3/4) 255-262.
- Lewis W. Tucker, George G. Robertson, "Architecture and Applications of the Connection Machine," Computer, vol. 21, no. 8, pp. 26–38, August, 1988.
- Arthur Trew and Greg Wilson (eds.) (1991). Past, Present, Parallel: A Survey of Available Parallel Computing Systems. New York: Springer-Verlag. ISBN 0-387-19664-1
- Charles E. Leiserson, Zahi S. Abuhamdeh, David C. Douglas, Carl R. Feynman, Mahesh N. Ganmukhi, Jeffrey V. Hill, W. Daniel Hillis, Bradley C. Kuszmaul, Margaret A. St. Pierre, David S. Wells, Monica C. Wong, Shaw-Wen Yang, and Robert Zak. "The Network Architecture of the Connection Machine CM-5". Proceedings of the fourth annual ACM Symposium on Parallel Algorithms and Architectures. 1992.
- W. Daniel Hillis and Lewis W. Tucker. The CM-5 Connection Machine: A Scalable Supercomputer. In Communications of the ACM, Vol. 36, No. 11 (November 1993).
- Gallery of CM-5 images
- CM-5 Manuals
- Tamiko Thiel on the visual design of the CM-1/2/200
- Feynman and the Connection Machine
- Liquid Selves, an animated short film rendered on a CM-2
- A preserved CM-2a at the Corestore Computer Museum
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Thinking Machines CM-5/1024
Numerical Wind Tunnel