请教，一个怪问题！

有哪位高人对下列程序做一个解释，我想知道“function DogCheck: longint; external;” 这个外部函数是怎么调用的，它在哪儿？万分感谢！！！！program Trainer;uses
  Windows,
  ...........{ The type of these six functions are longint }
  function DogCheck: longint; external;
  function DogConvert: longint; external;
  function WriteDog: longint; external;
  function ReadDog: longint; external;
  function DisableShare: longint; external;
  function GetCurrentNo: longint; external;
  function SetPassword: longint; external;
  function SetDogCascade: longint; external;
  {$L mhdelphi.obj}{$R *.RES}
var
   DogCascade: integer;
   ........
begin
  Application.Initialize;
     DogCascade := 0;
     dwRetCode := DogCheck();
     if (dwRetCode<>0) then {0 means susccess}
     begin
           szMessage := '请检查硬件狗是否存在，程序将退出！'+#13;
           Application.MessageBox(PChar(szMessage),'错误提示',0);
           EndRealtimeDatabase();
           Application.Terminate;
           exit;
     end;
     ConvertData:= '83499818';
     DogCascade:= 0;
     DogBytes:= 8;
     DogData:= @ConvertData[1];
     dwRetCode:= DogConvert();
     if dwRetCode<>0 then
     begin
          szMessage := '校验硬件狗失败，程序将退出！'+#13;
          //szMessage := szMessage + 'Error code is '+IntToStr(dwRetCode);
          //MessageBox(Handle, PChar(szMessage), PChar('错误提示'), 16);
          Application.MessageBox(PChar(szMessage),'错误提示',0);
          EndRealtimeDatabase();
          Application.Terminate;
          exit;
     end
     else
     begin
         if DogResult<>3402884680  then
         begin
          szMessage := '硬件狗校验值不匹配，程序将退出！'+#13;
          //szMessage := szMessage + 'Error code is '+IntToStr(dwRetCode);
          //MessageBox(Handle, PChar(szMessage), PChar('错误提示'), 16);
          Application.MessageBox(PChar(szMessage),'错误提示',0);
          EndRealtimeDatabase();
          Application.Terminate;
          exit;
         end;
     end;  FormSplash:=TFormSplash.Create(Application);
  FormSplash.Show;
  FormSplash.Update;  while FormSplash.Timer1.Enabled do
   Application.ProcessMessages;  F_SelMod:=TF_SelMod.Create(Application);
  F_SelMod.Show;
  F_SelMod.Update;
  FormSplash.Hide;
  FormSplash.Free;  while F_SelMod.Timer1.Enabled do
    Application.ProcessMessages;  if  SelModOkFlag then
  begin
   Application.CreateForm(TF_Trainer, F_Trainer);
   Application.CreateForm(TF_DllFun, F_DllFun);
   Application.CreateForm(TF_AlgList, F_AlgList);
   Application.CreateForm(TF_ShowOperation, F_ShowOperation);
   Application.CreateForm(TF_AddFault, F_AddFault);
   Application.CreateForm(TF_EFormList, F_EFormList);
   Application.CreateForm(TF_DelFault, F_DelFault);
   Application.CreateForm(TF_RunDpuWait, F_RunDpuWait);
  end
  else
  begin
    EndRealtimeDatabase();
    Application.Terminate;
  end;  Application.Run;end.