Cуществует ли диск в системе?

function DriveExists (Drive: Byte) : boolean;
begin
  Result := Boolean (GetLogicalDrives and (1 shl Drive));
end;

procedure TForm1.Button1Click(Sender : TObject);
  var Drive : byte;
begin
  for Drive := 0 to 25 do
    If DriveExists (Drive) then
    begin
      ListBox1.Items.Add (Chr(Drive+$41));
    end;
end;