The 0s and 1 s of the machine language were substituted by letters and symbols in assembly languages. The assembly languages use mnemonics (memory aid) in place of operation codes. The language uses symbols instead of numbers to write programs. A program written using such symbols in the assembly language is called the source program. The program written in assembly language has to be converted into machine language for use by the computer. This is achieved with the help of the assembler. The assembler is a system program which is supplied by the manufacturer. It converts the assembly program into a machine readable program and the resulting program is called the object program. Thus the input to the assembler is the source program and the output of the assembler is the object program. The assembler translates each assembly language instruction into a corresponding machine code.
It is relatively easy to write programs in assembly language as compared to machine language. They can be also modified relatively easily. However, like the machine language, assembly languages are also hardware dependant. When the machine changes, the program has to be changed.
Since the machine language and assembly language both are dependent on the hardware, they are referred to as low level programming languages. Both these languages require a deep understanding of the internal structure of the computer.
