A loadable driver has the same purposes as a nonloadable one, and uses the same interfaces to do its work. A loadable driver can be configured for automatic loading when its device is opened. Alternatively it can be loaded on command using the ml program (see the ml(1) and mload(4) reference pages).
A loadable driver remains in memory until its device is no longer in use, or until the administrator uses ml to unload it. A loadable driver remains in memory indefinitely, and cannot be unloaded, unless it provides a pfxunload() entry point (see "Entry Point unload()").
There are some small differences in the way a loadable driver is compiled and configured (see "Configuring a Loadable Driver").
One operational difference is that a loadable driver is not available in the miniroot, the standalone system administration environment used for emergency maintenance. If a driver might be required in the miniroot, it can be made nonloadable, or it can be configured for "autoregistration" (see "Registration").