Addressing within source modules: establishing addressability

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 in the following section.

Base Address Definition: A base address is the storage address that a given location counter value refers to when the program is loaded into memory. The location counter value is the location within the program (it is fixed relative to the start of the program). The corresponding storage address depends on where in memory the program is loaded.