From the studies it is observed that a typical procedure employs only a few passed parameters and local variables. Also the depth of procedure activation remains within a relatively narrow range.

To exploit these properties, multiple small sets of registers are used, each assigned to a different procedure.

A procedure call automatically switches the processor to use a different fixed size window of registers, rather than saving registers in memory.

Windows for adjacent procedures are overlapped to allow parameter passing.
The concept of overlapping register window is shown in the Figure 8.1.
                  
Figure 8.1: Overlapping register window