Assembler is a software that converts a program written in assembly language into machine code. There are usually one to one correspondent between assembly statements and machine language instruction. Machine language program in main memory of the computer and makes it ready for execution. Assembly language program after referred to as source program and its output is the machine language program often referred to as object program. During the process of translation the source program is not under execution assembler only coverts in into a from that the computer can execution.