| CPC G06F 3/0619 (2013.01) [G06F 3/0653 (2013.01); G06F 3/0679 (2013.01); G11C 29/50004 (2013.01)] | 18 Claims | 

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               1. A storage device comprising: 
            a memory device including a memory region which includes a first sub-region and a second sub-region; and 
                a controller configured to: 
                read assist data from a plurality of memory cells according to an assist read voltage during a read voltage adjusting operation on the first sub-region as a target sub-region, and 
                re-utilize the read assist data during the read voltage adjusting operation on the second sub-region as the target sub-region, 
                wherein the controller is further configured to: 
                read data from the target sub-region according to a target read voltage, 
                determine, based on the data and the assist data, a number of memory cells corresponding to the target read voltage, and 
                adjust the target read voltage based on the number of memory cells and an expected number of memory cells. 
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