Nonvolatile memory device, memory system, method of operating nonvolatile memory device, and method of operating memory system

A method of operating a memory system including a nonvolatile memory device that includes a 3D memory cell array and a memory controller configured to control the nonvolatile memory device, the method comprising:

• performing a first normal read operation on first memory cells connected to a first word line by using a first read voltage level;
• performing, if the first normal read operation fails, a read retry operation using a read retry voltage on the first memory cells, wherein the read retry voltage is set to a second read voltage level;
• selecting by the memory controller, a read offset table from a plurality of read offset tables based on a difference between the first read voltage level and the second read voltage level, wherein the selected read offset table stores a plurality of read voltage offsets, each of the read voltage offsets corresponding to a respective one of a plurality of word lines, and each of the read voltage offsets being used to determine a level of a read voltage in a normal read operation;
• sending, by the memory controller, a read voltage offset selected from the plurality of read voltage offsets of the read offset table to the nonvolatile memory device, wherein the selected read voltage offset corresponds to a second word line;
• and
• performing a second normal read operation on second memory cells connected to the second word line by using the selected read voltage offset.

A method of operating a nonvolatile memory device that includes a three-dimensional (3D) memory cell array, the method comprising:

• performing a plurality of read operations including a first read operation on the 3D memory cell array, wherein the first read operation is firstly performed on a first word line using a first read voltage level among the plurality of read operations;
• performing a read retry operation on the first word line using a second read voltage level after the first read operation is firstly performed and before a second read operation is secondly performed on a second word line;
• and
• generating a third read voltage level based on the first read voltage level and a read voltage offset of the second word line,
• wherein the second read operation is performed using the third read voltage level, wherein the first and second read operations are not read retry operations, and wherein the read voltage offset of the second word line is stored in a read offset table group.