As mentioned below, on Windows syscalls are highly unstable. They change with every single update to the OS. You have to call functions in ntdll and they in turn will call the kernel. Think of it like a kind of libc but one that must be dynamically linked. You can't statically link it because it's tied to the exact version of Windows you're using.

Of course Window's actual stable interface is the Win32 API, which will call ntdll which in turn makes the syscall.