Modes of Transfer: The data transfer between the CPU and the i/o device is through the memory. Data transfer between the CPU and I/O may be handled in a variety of modes. These are: Programmed I/O Interrupt I/O Direct Memory Access(DMA) Programmed I/O Mode : This mode uses the CPU as an intermediate path for the data transfer. Each data item is initiated by an instruction. Data transfer under this mode requires constant monitoring of the peripheral by checking the status flag which indicate whether the device is ready to receive or send the data. In this method the CPU stays in a program loop until the i/o unit is ready for data transfer. This method is quite slow. Interrupt I/O In this method instead