A memory system (1, 2, 110, 200, 410, 500) comprising: a memory device (50, 112, 220, 412, 520, 700); a buffer memory (214, 215, 514, 515) configured to store at least one of a Ready-To-Transfer, RTT, Universal Flash Storage-Protocol-Information-Unit, UPIU, and a response UPIU and implemented separately from the memory device (50, 112, 220, 412, 520, 700); and a memory controller (60, 111, 210, 411, 510) configured to acquire read data from the memory device (50, 112, 220, 412, 520, 700) in response to a read request received from an external host (10, 120, 300, 420, 600) and transmit a read data packet including the read data to the external host (10, 120, 300, 420, 600), wherein when the at least one of the RTT UPIU and the response UPIU stored in the buffer memory (214, 215, 514, 515) is present and when a size of the read data packet is equal to a minimum size of a read data packet that can be transmitted from the memory system (1, 2, 110, 200, 410, 500) to the external host (10, 120, 300, 420, 600), the memory controller (60, 111, 210, 411, 510) sends the at least one of the RTT UPIU and the response UPIU to the external host (10, 120, 300, 420, 600) after transmission of the read data packet is completed, wherein, when the at least one of the RTT UPIU and the response UPIU stored in the buffer memory is present and when a size of the read data packet is greater than the minimum size of a read data packet that can be transmitted from the memory system (1, 2, 110, 200, 410, 500) to the external host (10, 120, 300, 420, 600), the memory controller divides the read data packet into a first sub-data packet and a second sub-data packet and sends the at least one of the RTT UPIU and the response UPIU to the external host (10, 120, 300, 420, 600), alternately between the first sub-data packet and the second sub-data packet, and wherein the size of the first sub-data packet is the minimum size that can be transmitted from the memory system (1, 2, 110, 200, 410, 500) to the external host (10, 120, 300, 420, 600). a memory device (50, 112, 220, 412, 520, 700); a buffer memory (214, 215, 514, 515) configured to store at least one of a Ready-To-Transfer, RTT, Universal Flash Storage-Protocol-Information-Unit, UPIU, and a response UPIU and implemented separately from the memory device (50, 112, 220, 412, 520, 700); and a memory controller (60, 111, 210, 411, 510) configured to acquire read data from the memory device (50, 112, 220, 412, 520, 700) in response to a read request received from an external host (10, 120, 300, 420, 600) and transmit a read data packet including the read data to the external host (10, 120, 300, 420, 600), wherein when the at least one of the RTT UPIU and the response UPIU stored in the buffer memory (214, 215, 514, 515) is present and when a size of the read data packet is equal to a minimum size of a read data packet that can be transmitted from the memory system (1, 2, 110, 200, 410, 500) to the external host (10, 120, 300, 420, 600), the memory controller (60, 111, 210, 411, 510) sends the at least one of the RTT UPIU and the response UPIU to the external host (10, 120, 300, 420, 600) after transmission of the read data packet is completed, wherein, when the at least one of the RTT UPIU and the response UPIU stored in the buffer memory is present and when a size of the read data packet is greater than the minimum size of a read data packet that can be transmitted from the memory system (1, 2, 110, 200, 410, 500) to the external host (10, 120, 300, 420, 600), the memory controller divides the read data packet into a first sub-data packet and a second sub-data packet and sends the at least one of the RTT UPIU and the response UPIU to the external host (10, 120, 300, 420, 600), alternately between the first sub-data packet and the second sub-data packet, and wherein the size of the first sub-data packet is the minimum size that can be transmitted from the memory system (1, 2, 110, 200, 410, 500) to the external host (10, 120, 300, 420, 600).