40 in order to match the storage capacity 256 bytes or 512 bytes i e 128 or 256 words of page of the buffer 419 or a physical block b 0 each word w 0 w 1 w m of the mapping table 419 includes the address of a corresponding block b 0 b 1 b m therefore a mapping table 419 can correspond to 128 or less than 256 physical blocks b 0 therefore the physical blocks can be partitioned into a plurality of segments seg 0 u02dc seg n the number of blocks included in each partitioned segment will be limited within 256 or 128 of course each segment has a special reserved block as the symbol shown in fig2 b or as shown in fig2 c for exclusively recording mapping update each segment has a corresponding special reserved block for recording mapping update to built mapping relations of data the initial value of this mapping block is built when the system is initiating when the host computer 49 is to access a file the microprocessor 45 of the control device 40 will acquire the mapping table required to be read in by dividing the lba value introduced from the host computer 49 by the physical block number in the segment and then by the sector number in the block the mapping table of this segment will be stored into a mapping buffer 419 by the newest updated page of the special reserved block of mapping update thereby letting the system conveniently finding out the physical block address this lba required to map moreover each segment.