The global registers and the output registers can be used to hold 64-bit integer values, but the input registers and the local registers can only be used to hold 32-bit values in the lower half of the register. This is because the register save area for the input and local registers does not have enough room to store the full 64-bits and only the lower 32-bits are saved. The input and local registers may be saved and later reloaded at any point in time by a trap to handle an interrupt.