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A loader is a major component of an operating system that ensures all necessary programs and libraries are loaded, which is essential during the startup phase of running a program. It places the libraries and programs into the main memory in order to prepare them for execution. 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 needs to run.
The loader is a component of an operating system that carries out the task of preparing a program or application for execution by the OS. It does this 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 the memory. When all of that is done, the program is ready to execute. For small programs, this process is almost instantaneous, but for large and complex applications with large libraries required for execution, such as games as well as 3D and CAD software, this could take longer. The loading speed is also dependent on the speed of the CPU and RAM.
Not all code and libraries are loaded at program startup, only the ones required for actually running the program. Other libraries are loaded as the program runs, or only as required. This is especially true for applications such as games that only need assets loaded for the current level or location that the player is in.
Though loaders in different operating systems might have their own nuances and specialized functions native to that particular operating system, they still serve basically the same function. The following are the responsibilities of a loader: