1. A memory system comprising: an interface connected to a host including a main memory and a processor to control the main memory; and a control circuit that generates an initialization command among a plurality of initialization commands and transmits the generated initialization command to the host, the initialization command representing a command for instructing the host to execute initialization of the main memory and indicating an initialization method among a plurality of initialization methods for the main memory, the initialization method corresponding to a pattern of initialization data, wherein the initialization command generated by the control circuit indicates the initialization method using initialization data including a value obtained by any one of incrementing a predetermined initial pattern, adding a predetermined addition value to a predetermined initial pattern, shifting a value in a predetermined initial pattern, or performing an operation on a predetermined initial pattern by a predetermined algorithm.