Abstract: Flash is a type of electronically erasable programmable read- only memory (EEPROM). Flash memory is important as nonvolatile storage for mobile consumer electronics due to its low power consumption and shock resistance. NAND flash memory has many advantageous features as a storage medium, such as superior performance, shock resistance, and low power consumption. However, the erase-before-write nature and the limited number of write/erase cycles are obstacles to the promising future of NAND flash memory. An intermediate software layer called Flash Translation Layer (FTL) is used to overcome these obstacles. Many efforts for optimizing the working of address mapping schemes have been done by different research workers. Though various schemes are designed and proposed but there is no literature available providing mathematical computations comparing the performance of the various mapping schemes in the form of time complexity. In this paper we have tried to find out the comparative cost of block merge operation required during garbage collection for some representative mapping schemes like BAST and FAST .