You can use symbolic addresses in machine instructions and certain assembler instructions. This is much easier than explicitly coding the addresses in the form required by the hardware. Symbolic addresses you code in the instruction operands are implicit addresses, and addresses in which you specify the base-displacement or intermediate form are explicit addresses.

The assembler converts your implicit addresses into the explicit addresses required for the assembled object code of the machine instruction. However, for base-displacement operands, you must first establish addressability, as described below.

Base Address Definition: The term base address is used throughout this manual to mean the location counter value within a control section, element, or part from which the assembler can compute displacements to locations, or addresses. The base address need not always be the storage address of a control section, element, or part when it is loaded into storage at execution time.