An apparatus of a memory system and an operating method thereof include: memory blocks, each of the memory blocks includes strings, each of the stings has flash cells and select gates thereon, wherein the select gates of each of the strings with a same index number in each of the memory blocks are connected with each other, in each of the memory blocks, the strings are divided into groups, each of the groups includes at least one string, and each of the groups has own read counts management thereof.