An introduction to the concept of modules
When building the Linux kernel, the resulting image is a single file made by the linking of all object files that correspond to features enabled in the configuration. As a result, all included features are therefore available as soon as the kernel starts, even if the filesystem is not yet ready or does not exist. These features are built-in, and the corresponding modules are called static modules. Such a module is available at any time in the kernel image and thus can't be unloaded, at the cost of extra size to the final kernel image. A static module is also known as a built-in module, since it is part of the final kernel image output. Any change in its code will require the whole kernel to be rebuilt.
Some features (such as device drivers, filesystems, and frameworks) can, however, be compiled as loadable modules. Such modules are separated from the final kernel image and are loaded on demand. These can be considered as plugins that...