Nonvolatile memory device and method of operating the same

A nonvolatile memory device, comprising:

• a control unit configured to:
• calculate a threshold voltage distribution of each of selected pages, the threshold voltage distribution being calculated by repeatedly performing a read operation on each page from a start page to an end page while increasing a read voltage by a step voltage from a start read voltage to an end read voltage, in response to start page information and end page information of a command set for analyzing the threshold voltage distribution, the read operation being performed repeatedly until the read voltage reaches the end read voltage regardless of a compared result between the read voltage and threshold voltage of memory cells included in each of selected pages,
• compare the calculated threshold voltage distribution with a predetermined reference threshold voltage distribution, wherein the reference threshold voltage distribution includes information as to a distribution of threshold voltages of reference memory cells, and
• determine a read voltage having the least amount of errors for a subsequent read operation being performed according to the compared result.