A data processing system includes: a first memory system coupled to a host through a first external channel, a second memory system coupled to the host through a second external channel, and an internal channel suitable for coupling the first and second memory systems with each other, the host, when read-requesting first and second data to the first memory system, transfers a first external channel control information for selecting sole use of the first external channel or simultaneous use of the first and second external channels, to the first and second memory systems, the first memory system, when the first external channel control information indicates simultaneous use, the first memory system outputs the first data through the first external channel and outputs the second data through the internal channel, and the second memory system outputs the second data inputted through the internal channel, through the second external channel.