R0 = bit bucket and source of zero value R1 = target of ADDIL (Add Immediate Literal) R2 = RP Return Pointer where BL places address and where BV gets it R23 = fourth parameter of a procedure call R24 = third parameter of a procedure call R25 = second parameter of a procedure call R26 = first parameter of a procedure call R27 = DP Data Pointer to base of global data R28-29 = function result in R28 if 32-bits, both if 64-bits R30 = SP Stack Pointer to parameters and exit data R31 = receives target branch address in BLE instruction