Memory controller capable of performing multiple operations, an operation method thereof, a memory device, and a memory system

A memory system comprising:

• a memory module including a plurality of memory chips;
• a mirror memory module including a plurality of mirror memory chips corresponding to the plurality of memory chips, a first mirror memory chip of the plurality of mirror memory chips being storing same data as a first memory chip of the plurality of memory chips;
• and
• a memory controller configured to, in a system running state in which an operation according to a request of a user is capable of being performed after the memory system is booted, provide the memory module with a command for instructing a normal operation to be performed and provide the mirror memory module with a command for instructing a memory built-in self-test (MBIST) to be performed,
• wherein the MBIST is partially performed on the mirror memory module simultaneously with the normal operation performed on the memory module.