Hardware Delphi

Title: CD In/Out?
Question: How can I understand CD In/Out?
Answer:
private
procedure WMDeviceChange(var Msg: TMessage); message WM_DEVICECHANGE;
.
.
.
procedure TForm1.WMDeviceChange (var Msg: TMessage);
const
CD_IN=$8000;
CD_OUT=$8004;
var
Mesaj:String;
begin
inherited;
case Msg.wParam of
CD_IN:Mesaj:='CD-In';
CD_OUT:Mesaj:='CD-Out';
end;
end;