Editing Addressing mode (section)

===Memory indirect or deferred===
Any of the addressing modes mentioned in this article could have an extra bit to indicate indirect addressing, i.e. the address calculated using some mode is in fact the address of a location (typically a complete [[word (data type)|word]]) which contains the actual effective address. On some machines the indirect word could indicate indexing, indirection, tallying{{efn|Either increment or decrement.}} or some combination.

Indirect addressing may be used for code or data. It can make implementation of ''pointers'', ''references'', or ''[[handle (computing)|handle]]s'' much easier, and can also make it easier to call subroutines which are not otherwise addressable. Indirect addressing does carry a performance penalty due to the extra memory access involved.

Some early minicomputers (e.g. DEC [[PDP-8]], [[Data General Nova]]) had only a few registers and only a limited direct addressing range (8 bits). Hence the use of memory indirect addressing was almost the only way of referring to any significant amount of memory.

Half of the [[PDP-11 architecture|DEC PDP-11]]'s eight addressing modes are deferred. Register deferred @Rn is the same as register indirect as defined above. Predecrement deferred @-(Rn), postincrement deferred @(Rn)+, and indexed deferred @nn(Rn) modes point to addresses in memory which are read to find the address of the parameter. The PDP-11's deferred mode, when combined with the program counter, provide its absolute addressing mode.