The assembler language is the symbolic programming language that lies closest to the machine language in form and content. The assembler language is useful when:

• You need to control your program closely, down to the byte and even the bit level.
• You must write subroutines for functions that are not provided by other symbolic programming languages, such as COBOL, Fortran, or PL/I.

The assembler language is made up of statements that represent either instructions or comments. The instruction statements are the working part of the language and are divided into the following three groups:

• Machine instructions
• Assembler instructions
• Macro instructions