1. Translator lookahead controls for use with a main memory having a plurality of different storage units, the lookahead controls comprising, a plurality of segmentation registers for translating a part of an inputted logical address into physical block addresses contained in the segmentation registers, lookahead bistable positions being associated with each segmentation register for storing a lookahead coded signal for identifying a particular one of the storage units which contains a block being addressed by a loaded content of the segmentation register, means for selecting one of the segmentation registers to be loaded with an inputted physical block address, the lookahead bistable positions associated with each segmentation register being selected when the associated segmentation register is selected, means for generating the lookahead coded signal from the inputted physical block address being loaded into a selected segmentation register, and means for setting the coded signal into the selected lookahead bistable positions.