Difference Between Linker And Loader

Linker

A linker is a computer program that takes one or more objects generated by a compiler or an assembler and combines them into a single executable program. Computer programs are usually made up of multiple modules that can separate object files, each being a compiled computer program.  The program as a whole refers to these separately compiled files using symbols. The linker combines these separate files into a single, unified program, resolving the symbolic references as it goes along.

Linking is performed at both compile time when the source code is translated into machine code and load time, when the program is loaded into memory by the loader. Linking is performed at the last step in compiling a program.  

Linking can be of two types:

• Static linking
• Dynamic Linking

Dynamic linking is performed during the run time. This linking is accomplished by placing the name of a shareable library in the executable image. There is more chance of errors and failures. It requires less memory space as multiple programs can share a single copy of the library.   

Static linking is done during the compilation of source program. It takes collection of re-locatable object file and command-line argument and generate fully linked object file that can be loaded and run. The two main functions of static linking include:

• Relocation of code and data section and modification of symbol references to the relocated memory location.
• Association of each symbol reference with exactly one symbol definition. Each symbol has predefined task.

What You Need To Know About Linker

• A linker is a computer program that takes one or more objects generated by a compiler and combines them into a single executable program.
• Linker takes output of the language translator which is object code generated by compiler/assembler.
• Linking can be of two types: Static linking and Dynamic Linking.
• Linker is responsible for arranging objects in program’s address space.
• The linker links the object code and the header files and outputs the executable file.
• The linker combines all object module of a program to generate executable modules it also links the library function in the object module to built-in libraries of the high-level programming language.

Loader

A loader is the part of an operating system that is responsible for loading programs and libraries. It is one of the essential stages in the process of starting a program as it places programs into memory and prepares them for execution by OS.

Loader works by reading the contents of the executable file and then storing these instructions into the RAM, as well as any library elements that are required to be in memory for the program to execute. This is the reason a splash screen appears right before most programs start, often showing what is happening in the background which is what the loader is currently loading into memory.

Loading involves reading the contents of the executable file that contains the instructions of the program and then doing other preparatory tasks that are required in order to prepare the executable for running, all of which takes anywhere from a few seconds to minutes depending on the size of the program that require to run.

Responsibilities of a loader include:

• Link the starting point of the program and link any other required library.
• Initiates the registers.
• It validates the program for memory requirements, permissions, etc.
• Copy necessary files such as the program image or required libraries from the disk into the memory.
• Jump to the program starting point in memory.

Loader Can Be Of Three Types

• Absolute loading,
• Re-locatable loading
• Dynamic run-time loading

What You Need To Know About Loader

• The loader is the part of an operating system that is responsible for loading programs from executable files into memory, preparing them for execution and then executing them.
• The loader takes output of executable files generated by linker.
• Loader can be of three types: Absolute loading, Relocatable loading and dynamic run-time loading.
• Loader is responsible for adjusting references which are used within the program.
• The loader loads the executable file gained from the linker to the main memory.
• Loader allocates space to an executable module in the main memory.

Difference Between Linker And Loader In Tabular Form