The 1130 has no hardware support for a stack. Most subprograms are called with the instruction BSI (Branch and Store IAR). This deposits the value of IAR (the return address) at the destination address and transfers control to destination+1. Subprograms return to wherever they were called on that occasion using an indirect branch through that first word of the subprogram. Placing the return address in-line was a common technique of computers at that time, such as the Hewlett-Packard HP 2100 and the Scientific Data Systems SDS 920.