the point is to put a guard when performing indirection, that checks a type bit in the register. setting this bit is a privileged operation. unprivileged addres

the point is to put a guard when performing indirection, that checks a type bit in the register. setting this bit is a privileged operation. unprivileged address arithmetic can be performed if addresses also contain a bound. but the whole point is that you just cant hand any integer to the hardware and ask it to fetch.