Driver-based API
The API is "driver-based" when the kernel provides facilities but the file system code resides totally external to the kernel (not even as a module of a modular kernel).
It is a cleaner scheme as the filesystem code is totally independent, it allows filesystems to be created for closed-source kernels and online filesystem additions or removals from the system.
Examples of this scheme are the Windows NT and OS/2 respective IFSs.
Read more about this topic: File System API