   I found binary file is base byte.
  Is it true? if I do need 1 byte to save 1 info ,it will waster space.   
  Yes, one byte is the smallest amount of data you can manipulate.But don't you worry about that, even a 1 byte file will fill up at least one sector: anywhere from 512 bytes to 4kB or more. Plus all the extra data the OS needs to keep track of the file itself.   ;  This is true.  You have to store data at the byte level on most computers.  But a 1 byte file takes up a lot more than 1 byte of disk space, because they will usually take up a filesystem block which is often 1,024 to 8,192 bytes.