Loader and Link-editor

Loader and Link-editor: Once the assembler procedures an object program, that program must be placed into memory and executed. The assembler could place the object program directly in memory and transfer control to it, thereby causing the machine language program to be execute.        This would waste core by leaving the assembler in memory while the user’s program was being executed. Also the programmer would have to retranslate his program with each execution, thus wasting translation time. To over come this problems of wasted translation time and memory. System programmers developed another component called loader

“A loader is a program that places programs into memory and prepares them for execution.”

It would be more efficient if subroutines could be translated into object form the loader could”relocate” directly behind the user’s program. The task of adjusting programs o they may be placed in arbitrary core locations is called relocation. Relocation loaders perform four functions.

1.      Allocate space in memory for the programs.

2.      Resolve symbolic references between object decks (linking).

3.      Adjust all address-dependent locations, such as address constants, to correspond to the allocation space (relocation).

4.      Physically place the machine instructions and data into memory (loading).