That do be correct. That style of subroutine call goes back a _long_ way. IIRC, Whirlwind used that kind of linkage (alas, I've misplaced my copy of the Whirlwind instruction manual, sigh - a real tresure). ISTVR there was something about the way Whirlwind did it that made it clear how it came to be the way it was - IIRC, the last instruction in the subroutine was normally a 'jump to literal' (i.e. a constant, in the instruction), and the Whirlwind 'jump to subroutine' stored the return address in a register; there was a special instruction (normally the first one in any subroutine) that stored the low-order N bits of that register in the literal field of the last instruction: i.e. self-modifying code. The PDP-6 (of which the PDP-10 was a clone) was on the border of that period; it had both types of subroutine linkage (store the return in the destination, and jump to dest+1; and also push the return on the stack). Noel