Assembler

Assembler is software (program module) which converts assembly language code (source module) into a machine language code.

Types of Assemblers 

One Pass Assembler: 

• Goes (scans) through the program once
• Can resolve backward reference
• Cannot resolve forward reference

Two Pass Assembler: 

• Goes (scans) through the assembly language program twice
• First pass generates the table of the symbol, which consists of labels with addresses assigned to them
• Second pass uses the symbol table generated in the first pass to complete the object code for each instruction thus producing machine code
• It can resolve forward and backward reference both.

Backward reference	Forward reference
L1: …..       …..       …..       ….. JMP L1	JMP L1 ….. ….. ….. L1: …..