LOGICAL-T0-REAL ADDRESS TRANSLATION BASED ON SELECTIVE USE OF FIRST AND SECOND TLBS

Under such a condition between outputs of AND circuits for outputting All "0" when one of zero detecting circuits of two register identifiers within an instruction register detects "0", instead of a content of a general-purpose register designated by these identifiers, and also a carry derived from a page offset corresponding to an intermediate result of an address adder, when a page address portion of a logical address is known before this logical address is defined, selecting circuits are controlled, and then the address controller is bypassed to retrieve a translation look-aside buffer, thereby defining a real address. In case that the page address portion of the logical address register is identical to the page address portion of the base register, the translation look-aside buffer is previously retrieved in accordance with either the content of the index register, or the content of the base register so that the real address can be defined.