An assembler instruction is a request to the assembler to do certain operations during the assembly of a source module; for example, defining data constants, reserving storage areas, and defining the end of the source module. Except for the instructions that define constants, and the instruction used to generate no-operation instructions for alignment, the assembler does not translate assembler instructions into object code. The assembler instructions are described in Program structures and addressing, Assembler instruction statements, and How to write conditional assembly instructions.