Patent US 4,075,694

Apparatus is provided in connection with a computer memory for enabling a step by step transportation of an empty memory field containing a number of empty memory words from one side to the other of an adjacent data field containing a number of occupied memory words, while the computer is operative, by relocating the data field in such a manner that the information stored in each successive memory word adjacent to one border of the empty memory field is transferred to an empty memory word on the other border of the empty memory field, the latter field thus dividing the data field into two field portions which share said number of occupied memory words during the transportation. Incoming addresses, referring to a continuous area representing a data field being transferred, are converted so that the addresses instead refer to the two field portions. The continuous area is preferably identical with the relocated data field in one of its extreme positions, i.e. either the original position or the final position. By means of comparators the incoming addresses are compared with certain of the border addresses which delimit the field portions, thus determining whether or not the incoming address must be modified. When modification is to be made the address is incremented by an amount corresponding to the size of the empty memory field.