Function GetCDList : String;
Var
 I : Integer;
 Drives: Integer;
 Tmp : String;
begin
 Drives := GetLogicalDrives;
 Result := '';
 // units A=0 to el Z=25
 For I := 0 To 25 Do
 If (((1 Shl I) And Drives)<>0) Then
 Begin
 Tmp := Char(65+I)+':\';
 If (GetDriveType(PChar(Tmp))=DRIVE_CDROM) Then
 Result := Result+Char(65+I);
 End;
End;

procedure TForm1.Button1Click(Sender: TObject);
 begin
 Showmessage(GetCDList);
 end;