Assembler Directives and Operators
The major advantage of machine language programming is directly that the memory control is in the hands of the programmer, so that, he can be able to manage the memory of system more capably. Or else, the disadvantages are more. The coding, programming and resource management techniques are tiresome. The programme has to take care of the all these functions therefore the probability of human errors are more. The programs are hard to understand unless one has a thorough technical knowledge of instruction set and processor architecture.
The assembly language programming is simple as comparison of machine language programming. The instruction mnemonics are written in the assembly language programs directly. Now the programs are more readable for users than machine language programs. The major improvement in assembly language over the machine language is that the address values and the constants may be recognized by labels. If the labels are indicative, certainly then the program will become more understandable, and every time the programme will not have to bear in mind the different constants and addresses at which they are stored, throughout the programs. The labels might help to recognize the constants and addresses. Due to this service, the tedious byte handling and manipulations are got rid of. In similar manner, now different routines and logical segments might be assigned with labels rather than the different addresses. The memory control feature of machine language programming is not changed by providing storage define facilities in assembly language programming. The documentation facility that was not possible with machine language programming is now available in the assembly language.
An assembler is a program utilized to convert an assembly language program into the corresponding machine code modules which can further be converted to executable codes. Assembler decides address of each substitute and labels the values for each of the variables and constant. Then it forms the machine code for thedata and mnemonics in the assembly language program. Whilst doing these things, the assembler might find out syntax errors. The logical errors and others programming errors are not found out by the assembler. For finishing all these tasks) an assembler needs some hints from the programmer, for example: the need of the storage for a specific a variable or constant, types of the different routines ,logical names of the segments and modules, end of file, etc. These types of hints are given to the assembler by using some predefined alphabetical strings called assembler directives. Assembler directives help the assembler to properly understand the assembly language programs to prepare the codes.
Another type of hint which helps the assembler to assign a specificconstant witha label or initialise specific memory locations or labels with constants is called an operator. Rather than the operators perform and logical and the arithmetic tasks unlike directives that just direct the assembler to properly interpret the program to code it well. Following directives are commonlyused in the assembly language programming practice by using Turbo Assembler or Microsoft Macro Assembler.