We know that in any digital system or microprocessor system data are represented and stored in the form 0's and 1's called binary bits. These 0's and 1's are nothing but voltage levels. Low voltage level or zero voltage level correspond to 0 and high voltage level correspond to 1.
In a machine language instructions or data are stored as a combination of 0's ans 1's e.g. 00111100 is an instruction that increments the number in the register called the accumulator by one likewise all instructions (data) are stored in the form of 0's and 1's. Each machine(microprocessor) has his own set of instructions based on the design of its CPU
The biggest disadvantage of the machine language is that it is difficult to write programs in set of 0's and 1's and moreover it is error-prone also to recognize and write instructions in binary language. To remove this disadvantage, designers developed assembly language.