Method and data storage system for storing data in blocks without file reallocation before erasure

A memory management method is provided for a nonvolatile memory having a plurality of blocks each of which can be electrically erased and programmed. A data file to be stored in the nonvolatile memory is received. A number of blocks that are available for data storage are located from the plurality of blocks. The data file is stored in a first block of the number of blocks if the size of the data file is smaller than the total storage space of the first block. The data file is stored in the first block and a second block of the number of blocks if the size of the data file is larger than the total storage space of the first block but smaller than the total storage space of the first and second blocks. Unoccupied space of the first or second block by the data file is not used to store other data files such that no file reallocation operation is needed when the first or second block is to be erased. A data storage system having an erasable and programmable memory and a memory management program is also described.