1. A memory system which is connectable to a host, the memory system comprising: a first memory as a nonvolatile memory storing information associated with an address translation between a logical address and a physical address; a second memory temporarily storing a part of the information at least; a first controller executing a read operation and a write operation of the information for the second memory in a first data unit, the first data unit being changeable and being a data size of one of regions obtained by dividing in a first address space, the part of the information at least stored in the first memory; and a second controller executing a read operation and a write operation of the information for the first memory in a second data unit different from the first data unit.