1. In an electronic computer receptive of program subroutines including instructions and having a main memory for storing same therein, wherein said memory is sequentially searched for locating a stored instruction: section defining means responsive to a programmed instruction for defining at least two separate memory sections each having a predetermined initial memory address; jump means responsive to a second instruction following said programmed instructions for jumping to the first instruction of a subroutine stored in a predetermined one memory section, a booking register conditionable by said section defining means for temporarily storing the initial memory address of said predetermined section, a first memory origin register conditionable by said jump means for storing said temporarily stored initial memory address, and a program addressing register conditionable by said first memory origin register for sequentially addressing the instructions of said predetermined memory section departing from the initial memory address stored in said first memory origin register until said first instruction of subroutine is found.