20. Ambiguous moves: PTR directive

• Consider fragment of data definitions and code:

          .DATA
          table1 WORD 20 DUP (0)
          status BYTE 7 DUP (1)
          ..
          mov    EBX, OFFSET table1
          mov    ESI, OFFSET status
          mov    [EBX], 100
          mov    [ESI], 100
  

  The last two MOV instructions are ambiguous, since it is not clear whether the assembler should use byte or word equivalent of 100.

• WORD PTR and BYTE PTR type specifiers must be used for clarification:

          mov    WORD PTR [EBX], 100
          mov    BYTE PTR [ESI], 100