Control Structures in Illiac IV Fortran As part of an effort to design and implement a Fortran compiler on the ILLIAC IV, an extended Fortran, called IVTRAN, has been developed. This language provides a means of expressing data and control structures suitable for exploiting ILLIAC IV parallelism. This paper reviews the hardware characteristics of the ILLIAC and singles out unconventional features which could be expected to influence language (and compiler) design. The implications of these features for data layout and algorithm structure are discussed, and the conclusion is drawn that data allocation rather than code structuring is the crucial ILLIAC optimization problem. A satisfactory method of data allocation is then presented. Language structures to utilize this storage method and express parallel algorithms are described. CACM October, 1973 Millstein, R. E. array processing, parallelism detection, explicit parallelism, array allocation, parallel control structures, ILLIAC IV Fortran 4.12 4.21 4.22 CA731007 JB January 20, 1978 11:30 AM 2433 5 2433 2433 5 2433 2433 5 2433 2785 5 2433 2433 6 2433 2685 6 2433