Serial compilation and the 1401 FORTRAN compiler

The IBM 1401 FORTRAN compiler
¹
was designed as a set of phases that operate sequentially on the source program. The source program having been placed in core storage, the compiler phases enter core one at a time. Each phase overlays its predecessor, operates on the source program and, in turn, is overlaid by the next phase of the sequence. Thus, in contrast to the customary technique of passing the source program against the compiler in core, the compiler is passed against the source program which resides in core. It is assumed that the source program is more concise than the object program, and that an object program of interest can be accommodated in core.