Testando drives

Function TForm1.TemDiscoNoDrive(const drive : char): boolean;
var
DriveNumero : byte;
EMode : word;
begin
result := false;
DriveNumero := ord(Drive);
if DriveNumero >= ord('a') then
dec(DriveNumero,$20);
EMode := SetErrorMode(SEM_FAILCRITICALERRORS);
try
if DiskSize(DriveNumero-$40) <> -1 then
Result := true
else
messagebeep(0);
finally
SetErrorMode(EMode);
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
if TemDiscoNoDrive('a') then
ShowMessage('Tem disco no drive A:')
else
ShowMessage('Não tem disco no drive A:');
end;