Loadable kernel module

A loadable kernel module (LKM) is an executable library that extends the capabilities of a running kernel, or so-called base kernel, of an operating system. LKMs are typically used to add support for new hardware (as device drivers) and/or filesystems, or for adding system calls. When the functionality provided by an LKM is no longer required, it can be unloaded in order to free memory and other resources.

Most current Unix-like systems and Windows support loadable kernel modules but with different names, such as kernel loadable module (kld) in FreeBSD, kernel extension (kext) in macOS (although support for third-party modules is being dropped^[1]),^[2] kernel extension module in AIX, dynamically loadable kernel module in HP-UX,^[3] kernel-mode driver in Windows NT^[4] and downloadable kernel module (DKM) in VxWorks. They are also known as kernel loadable module (KLM), or simply as kernel module (KMOD).