Instruction Set Principles - Computer Architecture: A Quantitative Approach - page 500

Addressing Modes
Given an address, we now know what bytes to access in memory. In this subsection we will
look at addressing modes—how architectures specify the address of an object they will access.
Addressing modes specify constants and registers in addition to locations in memory. When
a memory location is used, the actual memory address specified by the addressing mode is
called the effective address .
Figure A.6 shows all the data addressing modes that have been used in recent computers.
Immediates or literals are usually considered memory addressing modes (even though the
value they access is in the instruction stream), although registers are often separated since
they don't normally have memory addresses. We have kept addressing modes that depend
on the program counter, called PC-relative addressing , separate. PC-relative addressing is used
primarily for specifying code addresses in control transfer instructions, discussed in Section
A.6 .