modem (মডেম) stands for mo = modulator and dem = demodulator. hence it makes analog to digital and digital to analog signals. when you pass a signal then it sends this signal to the BTS(base transceiver station) from MS(mobile station) and does reverse. so it is a input and output device.

mouse , keyboard = only for input becasue it sends signal to the computer.

plotter is an printing machine thus we can say it an output device.

টাচ স্কিনও একটি ইনপুট আউটপুট ডিভাইস।