We encountered an external call to the printf and ExitProcess API functions. These specific functions were developed for Windows as a means of communication between the user-mode and the kernel-mode. Generally, for most operating systems, the kernel is responsible for literally displaying the output on the monitor, writing files to the disk, reading keyboard strokes, transmitting data to USB ports, sending data to the printer, transmitting data to the network wire, and so forth. In essence, everything that has something to do with hardware has to go through the kernel. Our program, however, is in the user-mode, and we use the APIs to tell the kernel to do stuff for us.