1. A hybrid memory system, comprising: a central processing unit; a storage device configured to store user data and code data; and a main memory including a volatile memory and a nonvolatile memory, the main memory being configured to receive data necessary to perform an operation of the central processing unit from the storage device and to store the data, the volatile memory including a cache portion for data stored in the nonvolatile memory and a non-cache portion, wherein when data of the storage device is initially loaded to the main memory, data having a read-only property is stored in the nonvolatile memory and is not stored in the volatile memory, data having a read-write property is stored in the volatile memory and is not stored in the nonvolatile memory according to information of an initial allocation, wherein when data of the storage device is additionally loaded to the main memory by a request of the central processing unit, data having a read-only property is selectively stored in the nonvolatile memory and data having a read-write property is selectively stored in the volatile memory based on information of a page table, and wherein least recently used data among data stored in the cache portion of the volatile memory is migrated to the nonvolatile memory.