Готовность устройства
	
procedure TForm1.Button1Click(Sender: TObject); 
var OldErrorMode : Integer;   
    fp           : TextFile; 
begin   
 try
  OldErrorMode := SetErrorMode(SEM_FAILCRITICALERRORS);      
  try
   AssignFile(fp,'A:\foo.bar');
   Reset(fp);
   CloseFile(fp);
  finally
   SetErrorMode(OldErrorMode);      
  end;    
 except
  on E:EInOutError do 
    if E.ErrorCode = 21 then
       ShowMessage('Drive A: is not ready...');    
  end; 
end;