Base address
In computing, a base address is a memory address serving as a reference point for other addresses within a data structure. Related addresses can be accessed using an addressing scheme.
Under the relative addressing scheme, to obtain an absolute address, the relevant base address is taken and an offset is added to it. Under this type of scheme, the base address is the lowest-numbered address within a prescribed range, to facilitate adding related positive-valued offsets.
In IBM System/360 architecture, the base address is a 24-bit value in a general register, and the offset is a 12-bit value in the instruction.