Получить имена свободных com портов

procedure TForm1.Button1Click(Sender: TObject);
var
  reg: TRegistry;
  st: TStrings;
  i: integer;
begin
  reg := TRegistry.Create;
  reg.RootKey := HKEY_LOCAL_MACHINE;
  reg.OpenKey('hardware\devicemap\serialcomm', false);
  st := TStringList.Create;
  reg.GetValueNames(st);
  for i := 0 to st.Count - 1 do
    Memo1.Lines.Add(reg.ReadString(st.Strings[i]));
  st.Free;
  reg.CloseKey;
  reg.free;
end;