The Extensible Firmware Interface

#include "efi.h"
EFI_STATUS
InitializeHelloApplication (
    IN EFI_HANDLE         ImageHandle,
    IN EFI_SYSTEM_TABLE   *SystemTable
    )
{
    UINTN Index;
    SystemTable->ConOut->OutputString(SystemTable->ConOut,
        L"Hello application started\n");
    SystemTable->ConOut->OutputString(SystemTable->ConOut,
        L"\n\r\n\r\n\rHit any key to exit this image\n\r"); 
    SystemTable->BootServices->WaitForEvent(
        1, &(SystemTable->ConIn->WaitForKey), &Index);
    SystemTable->ConOut->OutputString(SystemTable->ConOut, 
        L"\n\r\n\r");
    return EFI_SUCCESS;
}

Example 1: Routines supported by the firmware.