Register window isn't used for context switching, it's used during function calls. In most architectures the sliding is done implicitly during by the call/ret i

Register window isn't used for context switching, it's used during function calls. In most architectures the sliding is done implicitly during by the call/ret instructions (named eg call4 ret4 to slide 4). Some architectures allow you to also slide the window manually but none (that I know of) allows you the absolute positioning needed to mimic traditional register files/banking.