Abstract—The structure of ILLIAC IV, a parallel-array computer containing 256 processing elements, is described. Special features include multiarray processing, multiprecision arithmetic, and fast data-routing interconnections. Individual processing elements execute 4×106instructions per second to yield an effective rate of 109 operations per second.

An on-line man-computer program has been described and experimental results concerning the demands made upon the computer are reported. For this particular system it would appear unwise to attempt a time-sharing with other programs on most systems. The use, however, as a single multicomponent program is quite reasonable. It is felt that the functions that are defined and measured here are sufficiently similar to those involved in other on-line systems that these results should be of some concern to those proposing to time-share them. In any event, this work points up the need for experimental evaluation of programs proposed for on-line use before incorporation in a time-sharing system. The author gratefully acknowledges the assistance of D. Mortara in helping to devise the experimental monitoring system and of R. Trogdon and J. Knoke for their technical assistance in the measurements.