Key Difference – Linker vs Loader
A computer program is used to give instructions to the computer. It is written using a specific programming language. Programming languages such as C, Java are high level programming languages and they are understandable by humans but not by the computer. Therefore, a high level program is converted into machine language using a language translator. A program written using a high level language is a source code. After the conversion, the translated code is called the object code. The linker and loader are two software programs that are used for program execution. This article discusses the difference between Linker and Loader. Linker is the software that links the object code with additional files such as header files and creates an executable file with .exe extension. The loader is the system software that loads the executable file generated by the linker to the main memory. That is the key difference between Linker and Loader.
CONTENTS
1. Overview and Key Difference
2. What is Linker
3. What is Loader
4. Relationship Between Linker and Loader
5. Side by Side Comparison – Linker vs Loader in Tabular Form
6. Summary
What is Linker?
A computer program is a set of instructions given to a computer to perform a certain task. A computer program can be written using a programming language. Most programming languages are high level programming. They are easily understandable and readable by the programmer. Those languages follow a syntax similar to the English language. Some examples of high level languages are Java, C, and Python. A program written using a high-level programming language is known as the source code, source file or source program. The extension of the source code depends on the language it was developed with. If the source code is written in C++, then the file extension is .cpp. If the source code is written in Python, the extension is .py.
Even the source code is understandable by the programmer; it is not understandable by the computer. Therefore, the source code should be converted into machine understandable format using a language translator. It can be a compiler or an interpreter. The translated code is known as the object code. The object code is in machine language. It consists of zeros and once. The computer can directly understand the object code. It has the extension .obj. If there is a source code as Test.c, it goes through the compiler and converted code becomes Test.obj.
Linker is the software that links the object code with additional files such as header files and creates an executable file with .exe extension. The program might have used built-in functions. The functionalities for those built-in functions are in the header files. According to the above-explained example, the object code which is Test.obj is added with necessary header files using the Linker. It creates a new file known called Test.exe. It is an executable file. Therefore, it is executable by the computer.
What is Loader?
A program that should execute must be placed in the memory. The linker links the object code and header files and output the executable file. The loader is the system software that loads the executable file generated by the linker to the main memory. It allocates the memory space to the executable module in main memory. Therefore, a loader is a part of the operating system that is responsible for loading programs and libraries.
Figure 01: Order in which the Source Code loads to the Memory
Loading a program involves several steps. It involves reading the contents of the executable file containing the program instruction into memory and also to carry out the necessary preparing tasks to run the executable file. Once loading is completed, the operating system starts the program by passing control to the loaded program code. Special computer systems such as Embedded systems generally do not have loaders. The code executes directly by the ROM.
What is the Relationship Between Linker and Loader?
- The output of the Linker goes to the Loader.
What is the Difference Between Linker and Loader?
Linker vs Loader |
|
| Linker is the software that links the object code with additional files such as header files and creates an executable file with .exe extension. | The loader is the system software that loads the executable file generated by the linker to the main memory. |
| Input | |
| The linker takes the output of the language translator, which is the object code. | The loader takes the output from the linker, which is the executable file. |
| Functionality | |
| The linker links the object code and the header files and outputs the executable file. | The loader loads the executable file gained from the linker to the main memory. |
Summary – Linker vs Loader
Linker and Loader are two software components related to program execution. This article discussed the difference between the Linker and the Loader. Linker is the software that links the object code with additional files such as header files and creates an executable file with .exe extension. The loader is the system software that loads the executable file generated by the linker to the main memory. That is the difference between Linker and Loader.
Reference:
1.’Loader (computing)’, Wikipedia, Wikimedia Foundation, 28 Feb. 2018. Available here