Static and Dynamic Loader in Operating System

An Operating system is the critical component for managing the various memory resources in the computer system. One of the essential tasks of the operating system is to manage the executable programs or applications in the computer system. A program needs to be loaded into the memory for the purpose of execution. For the execution context, the loader comes into the picture.

What is Loader?

A loader is a module that is the essential part of the operating system, that is responsible for loading the program from secondary memory to main memory and executing them. 

• The main function of the loader is to locate the executable file inside the file system.
• The loader allocates memory to store the program and once the memory is allocated then it loads the program in that memory space.
• The loader is also responsible for resolving the external dependencies such as references, and system libraries mentioned inside the program.
• Loaders are responsible for ensuring the correct loading of the program inside the memory.
• There are two types of loading in the operating system, Static and Dynamic Loading.

Types of Loader

Loaders in operating systems can be categorised into several kinds based totally on their functionality and how they manage the loading technique. But there are mainly two types of loader:

• Static Loader
• Dynamic Loader

Here below is a brief discussion of the types of loaders:

Static Loader

The static loader is a program that loads the entire executable program including, libraries and dependencies required by the program into the memory before the program gets executed.

• After loading the program into the memory, the loader resolves all the external dependencies in the program, this process is known as static linking.
• Once the linking is done, the loader updates the address of the program.
• No additional software is needed for loading and linking the entire program. 
• Static linking is applied for the static loader.
• Static loader is portable as it can work in any platform which supports the executable format used by the program.

Features of static Loader

• Pre-loading: Static loaders load all vital program modules into memory before execution starts.
• Compilation Time Linking: The method of linking and loading occurs at some point of the compilation segment of the program. This way that linking addresses and dependencies are resolved at assemble time.
• Predictable Execution Environment: Since all modules are loaded into memory before execution, the execution environment is predictable and deterministic.
• Faster Startup Times: Due to pre-loading, static loaders commonly have quicker startup instances in comparison to dynamic loaders due to the fact there's no need to load modules at some stage in runtime.
• No Runtime Overhead: Once the loading is done, the program may be finished without delay without any extra overhead from the loader.

Advantages of Static Loader

• Static loaded is easy and simple to implement.
• As the entire program is loaded into the memory once, this makes the static loaded very much faster.
• Static loaded is reliable because it resolves all the external references before the execution of the program.

Disadvantages of Static Loader

• The main disadvantage of static loaded is wastage of memory because its load all the data and code into memory before execution. 
• Static loader is not flexible as it does not handles the dynamic loading of the data.
• Static loader is not efficient as the data or code that it loads, it may or may not be executed after.
• Static loader is inflexible because it does not adapt the changes in the program's requirement at dynamic environment.

Dynamic Loader

While executing a process, the entire program and the required process data should be present in the physical memory which in terms limits the process size with the size of physical memory. For proper utilization of physical memory, dynamic loader comes in picture.

• The dynamic loader is a program that loads the program into the main memory on demand. 
• Dynamic loader loads only the required code an data by the program and leaves the rest part in the executable file.
• Dynamic loader resolves all the external dependencies and the entire process is known as dynamic linking.
• Dynamic loader is very useful when a large amount of data need to handled in the efficient manner.

Features of Dynamic Loader

• On-demand Loading: Dynamic loaders load program modules into memory as they're needed throughout runtime. This means that best the important modules are loaded into memory when required.
• Runtime Linking: The method of linking external dependencies takes place in the course of runtime.
• Reduced Memory Footprint: Dynamic loaders can reduce memory usage by using loading most effective the required modules into memory.
• Dynamic Updates: Dynamic loaders help dynamic updates to this system throughout runtime. New modules or variations of modules can be loaded and related with out restarting this system.
• Support for Shared Libraries: Dynamic loaders are generally used in structures with shared libraries, allowing a couple of packages to proportion code in memory.

Advantages of Dynamic Loader

• Dynamic loader is very much memory efficient as it loads only the necessary data and code for the execution.
• Dynamic loader is very much flexible because it can adapt the changes in the program's requirement at dynamic environment.
• Dynamic loader can reduce the executable file size by excluding the libraries and dependencies from the binary.

Disadvantages of Dynamic Loader

• Dynamic loader is more complex and it is difficult to implement.
• Dynamic loader is having high overhead as it resolves all the external dependencies at run time.
• Dynamic loader takes longer time to load the program in the memory.
• Dynamic loader is portable as it is not platform independent. It may not work in all the platform because of dynamic linking mechanism.
• Dynamic loader is less reliable because it resolves the external dependencies in runtime which may sometimes lead to error.

Performance Comparison of Static and Dynamic loader

Difference Between Static and Dynamic Loader 

Conclusion

In conclusion, loaders play a critical position in the execution of programs inside running systems. They are responsible for loading programs into memory and preparing them for execution. Throughout this discussion, we have explored numerous kinds of loaders, inclusive of static loaders and dynamic loaders.

Static loaders load all necessary application modules into memory earlier than execution. On the other hand, dynamic loaders load modules into memory as they may be wanted throughout runtime, presenting flexibility and performance in memory usage. In this article we have mentioned several advantages and disadvantages of the static and the dynamic loader. For more details you can refer Difference between Loading and Linking in Operating System and Difference between Static and Dynamic Loading.