A receiver included in a memory device includes a flag generator circuit, an equalizer circuit and an equalization controller circuit. The flag generator circuit is configured to, during a normal operation mode, generates a flag signal without an external command. The equalizer circuit is configured to, during the normal operation mode, receive an input data signal through a channel, generate an equalized signal by equalizing the input data signal based on an equalization coefficient, and generate a data sample signal including a plurality of data bits based on the equalized signal. The equalization controller circuit is configured to, during the normal operation mode, determine an amount of change in the equalization coefficient based on the flag signal, the equalized signal and the data sample signal, and perform a training operation in which the equalization coefficient is updated in real time based on the amount of change in the equalization coefficient.