Connection Machine

A Connection Machine (CM) is a member of a series of massively parallel supercomputers that grew out of doctoral research on alternatives to the traditional von Neumann architecture of computers by Danny Hillis at the Massachusetts Institute of Technology (MIT) in the early 1980s. Starting with CM-1, the machines were intended originally for applications in artificial intelligence and symbolic processing, but later versions found greater success in the field of computational science.

Danny Hillis and Sheryl Handler founded Thinking Machines Corporation (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 hypercube-based 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 central processing unit (CPU) nodes, its memory handling, and the programming language Lisp applied in the parallel machine.

Each CM-1 microprocessor has its own 4 kilobits of random-access memory (RAM), and the hypercube-based 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 subcube contains 16 printed circuit boards and a main processor called a sequencer. Each 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 hypercube-based routing network, a main RAM, and an input-output processor (a channel controller). 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. Nobel Prize winning physicist Richard Feynman had previously calculated that 5 buffers would be enough, using a differential equation involving the average number of 1 bits in an address. They resubmitted the design of the chip with only 5 buffers, and when they put the machine together, 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 discovered that the CM-1 would compute the Feynman diagrams for quantum chromodynamics (QCD) calculations faster than an expensive special purpose machine developed at Caltech.

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