Memory Mapped I/O and Isolated I/O are two methods of performing input-output operations between CPU and installed peripherals in the system.
Memory Mapped I/O:
Memory mapped I/O uses the same address bus to connect both primary memory and memory of hardware devices (registers). Memory and registers of I/O devices gets assigned values, thus when CPU try to access an address value, it can either from memory or from registers of I/O devices. Memory mapped I/O thus helps in utilizing the same instruction for accessing or addressing both primary memory and I/O device memory locations.
Isolated I/O uses separate instruction classes to access primary memory and device memory. In this case, I/O devices have separate address space either by separate I/O pin on CPU or by entire separate bus. As it separates general memory addresses with I/O devices, it is called isolated I/O. As the peripheral devices are slower than the memory devices, I/O operations can be slow. Isolated I/O accelerates I/O operations by using separate buses.