Nt
Windows system services (most of which are exported as Windows functions)
Ob
Object manager
Po
Power manager
Pp
PnP manager
Ps
Process support
Rtl
Run-time library
Se
Security
Wmi
Windows Management Instrumentation
Zw
Mirror entry point for system services (beginning with Nt) that sets previous access mode to kernel, which eliminates parameter validation, because Nt system services validate parameters only if previous access mode is user