Correct Statements ???
S1 : Generally I/O mapped I/O technique is used to connect more number of I/O devices then memory mapped I/O technique.
S2 : Processor generates memory read (MRD) and memory write (MWR) control signals while communication with I/O devices in memory mapped I/O technique.
S3 : In Isolated I/O : the maximum number of I/O devices that can be addressed by the processor is $2^{20}$ when port address size is 16 bit.
S4 : While communication the I/O devices in I/O mapped I/O, the valuable memory space address is wasted due to the utilization of this memory space address to the I/O devices.