A method for accessing a memory of a computer system for BIOS codes optionally performs a detection procedure to realize a maximum memory burst read size of the memory according to a flag value upon the computer system is initialized. For example, the detection procedure is performed when the flag value is logic “1” and the detection procedure is not performed when the flag value is logic “0”. When the detection procedure is performed, read requests with sequentially reduced memory burst read sizes are asserted to the memory one by one until the maximum memory burst read size of the memory is realized. Then, the BIOS codes are read from the memory with the maximum memory burst read size.