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Linker & Loader are utility programs that play an important part in program execution. Before execution, a program’s source code travels via the compiler, assembly, linker, and Loader in the sequence listed before execution. On the one hand, the linker consumes the Assembler’s object codes and combines them to form the executable module. On the other hand, the Loader loads the above executable module into the main memory to be executed. Let us use a comparison graphic to explain the difference between a linker and a loader.
What is Linker?
The Assembler creates object code from a source program and passes it to the linker. The linker uses this object code to build executable code again for the program, which it then passes on to the Loader. Programs written in high-level languages include libraries & header files. The source code may include some library functions, the definitions of which are kept inside the built-in libraries. These functions are linked to a built-in library by the linker. If the built-in libraries aren’t discovered, the compiler is notified, and the error is generated.
Large programs are sometimes broken into subprograms known as modules. The source program’s object modules are created whenever these modules are built and assembled. The linker is in charge of combining/linking all the object modules to produce a single executable of the source program.
There are two kinds of linkers.
- Linkage Editor: A linker that creates a relocatable, executable module.
- Dynamic Linker: It defers/postpones the linking of some external modules till the load module/executable modules are produced. Linking occurs throughout the load or run time.
What is Loader?
The software that must be run is stored in the main memory. Load an executable file into the operating system, Loader. The loader allocates memory space in the main memory to the executable module. Absolute loaders, relocatable loaders, and dynamic program execution loading are the three types of loaders. These three loaders use different loading approaches: absolute, relocatable, and dynamic run-time. The absolute injector loads the program’s executable file into the same primary memory region. The assignment must be known to the programmer in absolute Loader. The loader builds or assembles the real main memory location. When an instruction is performed, a dynamic program execution loader, an absolute memory program, is produced.
Here are three techniques for loading:
- Loading in absolute terms
- Loading is movable.
- Run-time dynamic loading
- Absolute loading: This method loads a program’s executable file into the same main memory region each time. However, it has significant drawbacks, requiring a programmer to understand the assignment mechanism for loading modules into the main memory. If the program is to be amended, including some insertion and deletion, then all of the program’s addresses must be changed.
- Relocatable loading: The compiler and Assembler do not create the real main memory location in this technique. It generates relative addresses.
- Dynamic Run-Time Loading: In this method, the exact address for a program is produced when an executable module’s instruction is executed. The preloaded module/executable module may be loaded into any section of main memory, making it extremely versatile. The running application can be halted and switched out to a disc before returning to the main memory at a different primary address.
Linker Vs. Loader:
When executing any program, the linker and loader are crucial. They are utility applications that assist a program while it is running. A linker’s primary goal is to generate executable files, whereas a loader’s primary goal is to put executable files into memory. Let’s look at some more distinctions between a linker and a loader.
Key Differences Between Linker and Loader
| Linker | Loader |
| A linker is a useful utility tool that joins the object files created by the assembly and compiler, as well as additional code, into a single executable | A loader is an essential component of an os that is in charge of loading applications and libraries |
| It accepts the object code created by an assembler as input. | It accepts linker-generated executables. Modules. |
| It assembles all object modules in a source code file to create an executable module. | It assigns the locations to a main memory executable module for execution. |
| It produces an executable module from a source programme. | It inserts the executable module into the main memory. |
| It is in charge of handling the items in the program’s space. | It is in charge of creating references that are used throughout the application. |
