OPERATING METHOD OF MEMORY CONTROLLER AND NONVOLATILE MEMORY DEVICE

A default read operation is performed on a page using a default read voltage set to generate default raw data. If error bits of the default raw data are not corrected, a plurality of low-level read operations is performed on the page using a plurality of read voltage sets to generate a plurality of low-level raw data. Each read voltage set is different from the default voltage set. A read voltage set is selected from the plurality of read voltage sets as a starting voltage set, according to each low-level raw data. A high-level read operation using the selected starting voltage set is performed on the page to generate high-level raw data.