Final answer:
The relocation register's primary function is to provide each process with a unique address space by converting logical addresses to physical addresses on a machine, ensuring process isolation and security.
Step-by-step explanation:
The relocation register is used in operating systems to help manage the process address space. When considering its primary function in a system, the best answer is b) A different address space to processes. The relocation register holds the value added to a program's address to convert a logical address space to a physical address on the machine. This offers each process the illusion of having its unique address space and protects the address spaces of individual processes from each other. This mechanism ensures that no two processes can interfere with each other's addresses, providing an important layer of security within the system. While it indirectly contributes to the memory protection of processes, the key role of the relocation register is to ensure that each process operates within its assigned address space.