Minicomputer systems

By Richard H. Eckhouse

Subjects: Programming, Minicomputers, Computer programming, Pdp-11 (computer), Computers, PDP-11 (Computer)

Description: The front cover depicts a schematic of Prof. Derek de Solla Price's analysis of the 2000-year-old Antikythera gear mechanism, which is described on the back cover: The oldest known minicomputer system, the Antikythera mechanism, was created circa 80 B.C. by an ancient mechanician, possibly on the island of Rhodes. A party of sponge fishers discovered fragments of the device in a shipwreck off Antikythera, northwest of Crete, in 1900. This instrument predates any known mechanical system of similar complexity by hundreds of years and is thus the oldest existing relic of scientific technology. The fragments of the instrument were "reconstructed" and the function of the mechanism decoded primarily through the efforts of Derek de Solla Price, presently Avalon Professor of History of Science at Yale University. The gears, schematically depicted on the cover, were all fashioned from a single bronze sheet and were encased in a rectangular box about 17 cm wide, 32 cm high, and 9 cm deep. Two sets of rotatable annular dials, upper and lower, filled the back cover while a single dial with two annuli, the inner fixed and the outer moveable, was centrally located on the front. The device was apparently a portable hand-calculator for displaying calendrical cycles. System input was via the crown-gear wheel at the right; five turns moved the mechanism dials through a yearly cycle. System output, via the dial pointers, was a visual indication of various astronomical phenomena, such as the motions of the sun and moon in the zodiac, and risings and settings of bright stars and constellations throughout the year. The device is the true predecessor of the modern minicomputer system by virtue of its sophisticated differential turntable, which has no known historical precedent. The synodic motion of the moon, the cycle of phases from new moon to full moon, is the difference between the sidereal motions of the sun and moon against the background of fixed stars. The differential gear apparently computes and, via the dials, displays positional information regarding these cycles for any time of year. The provenance, decoding, function, and historical significance of the Antikythera mechanism is fully documented in Dr. Price's monograph, "Gears from the Greeks", Science History Publications, New York, 1975.