All OS services, except those provided by the mandatory
microkernel/process manager module (procnto), are
handled via standard processes.
A richly configured system could include the following:
filesystem managers
character device managers
native network manager
TCP/IP
System processes vs user-written processes
System processes are essentially indistinguishable from any user-written program—they use the same public API and kernel services
available to any (suitably privileged) user process.
Device drivers
Device drivers allow the OS and application programs to make use of the underlying hardware in a generic way (e.g., a disk
drive, a network interface).