To aid the programmer, the assembler optionally generates an output listing of the source statements, machine code, memory locations, error messages, and other information useful in debugging and verifying programs. The assembler has a number of directives that control the operation of the assembler. For example, the .TITLE directive controls the identifying title that the assembler prints on the pages of the output listings; the .BYTE directive instructs the assembler to generate data in memory bytes.