Question

1A. With a neat diagram, explain the various components of language processing 3M system

Answer 1

We needed a system that helps us to program in our own language and execute it . But since the system cannot understand this language, we need a mechanism which converts the high level language that we program with to a machine level program and execute it. On this high level language program, we may be using tools or modules that are residing outside this program therefore we also need to include these files to our code. The system that does this task is known as language processing system. There are many steps involved in this other than specified above. We look into the components of language processing system and explain each.

Source Program Pno cesso Pre wa Comn pilet Torga Assum bly progarr Assemble Reloatable madin Pagam module

Note : Source program is not a component. We can say it as an input to the system. (Source program is the program that we code in high level language)

Pre processor :

Input :Source program

Output :Source program

The source program is first handled by the pre processor. It import/include different other program/program segments or modules to have a complete environment so that the source program can run.Therefor the pre processor will convert our source program into a different version of source program. The best example for this the include statements that we write above C/C++ and using the functions defined in those libraries. In C/C++ any statement started with '#' is handled by pre processor. The examples are macros (using #define). Consider a statement # define pi 3.14. The pre processor replace all the occurrences of the of pi in code with 3.14

Compiler:

Input :Source program

Output :Assembly code

The compiler do the compilation. Compilation is defined as the process of translating one language to other. Here the compiler will translate the given source code into a target assembly language. There are many benefits for doing this. The most important benefit is easiness. Assembly language are easy to debug. In most of the time code optimization is also done in assembly code.

Assembler:

Input :Assembly code

Output :Relocatable Machine code

It will convert the assembly code (from compiler) to actual executable code.

Now the important question comes..., If it assembler returns the executable code, then what is Linker/Loader.

In machine language, the address for each module will be in relocatable machine code format. This is done so that even if we change one module, we don't have to re write the entire code. We just have to locate the address to new written module. Therefore the actual output of assembler is not machine code, but a relocatable machine code. This is given as input to Linker/Loader

Linker/Loader:

Input Linker :Relocatable machine code

Output Linker :Target machine code

The linker will link each and every module of program to other some other modules or modules whose definitions are written outside. So different modules will get linked so that the program will become ultimately an executable one. It will also create an header to the target program so that when the program gets executed, then from the header part of the program, the Operating System can get the required information and do the needful loading. Then Loader will come into play. When the program will be asked for execution, each and every program is requiring some memory space to get loaded. The loader will check for available memory blocks, where the program can get loaded and can have its smooth execution. Therefore, in the end, linker will returns the target machine code which will be loaded by loader prior to execution.