Nonvolatile memory device, memory controller, and reading method of storage device including the same

A memory controller comprising:

• a processor;
• control pins configured to provide control signals to at least one nonvolatile memory device including a first memory area connected to a first word line;
• an error correction circuit configured to correct data read from the at least one nonvolatile memory device based on the control signals;
• and
• a buffer memory configured to store a plurality of tables for compensating for a reading level of a reading operation of the at least one nonvolatile memory device,
• wherein the processor is configured to input a first read command for performing a first reading operation on the first memory area using at least one variation table stored in the at least one nonvolatile memory device.

A reading method of a storage device, the reading method comprising:

• performing, in at least one nonvolatile memory device, a first on-chip valley search (OVS) sensing operation on selected memory cells in response to a first read command received from a memory controller;
• extracting variation information of threshold voltages of the selected memory cells and deterioration information of a memory block including the selected memory cells;
• performing a first main sensing operation at a modified reading level based on the variation information and the deterioration information;
• and
• outputting a result of the first OVS sensing operation and data of the first main sensing operation to the memory controller,
• wherein the first OVS sensing operation and the first main sensing operation are defined as a first reading operation.