Explain Register Window with appropriate window.

When a procedure is called, the register window shifts by sixteen registers, hiding the old input registers and old local registers and making the old output registers the new input registers.
Input registers : arguments are passed to a function
Local registers: to store any local data.
Output registers: When calling a function, the programmer puts his argument in these registers.

Circular Arrangement of Register Window

Make very fast procedure calls as they avoid the need to save a processor’s current in memory, further reducing off-chip traffic.
Instead, the state variables are held in the current window, and the next window is opened for the new procedure.
A refinement on this idea in that the input and output registers of adjacent windows overlap, allowing variables and parameters to be passed to the next process without physically moving data.
The additional registers are hidden from view until you call a subroutine or other function. Where other processors would push parameters on a stack for the called routine to pop off, SPARC processors just "rotate" the register window to give the called routine a fresh set of registers.
The old window and the new window overlap, so that some registers are shared.