function IsDriveReady(DriveLetter : char) : bool;
var
  OldErrorMode : Word;
  OldDirectory : string;
begin
  OldErrorMode := SetErrorMode(SEM_NOOPENFILEERRORBOX);
  GetDir(0, OldDirectory);
  {$I-}
    ChDir(DriveLetter + ':\');
  {$I+}
   if IoResult <> 0 then
    Result := False
   else
    Result := True;

  ChDir(OldDirectory);
  SetErrorMode(OldErrorMode);
end;

function IsDriveReady(DriveLetter : char) : bool;
var
    OldErrorMode : Integer;
    fp                     : TextFile;
begin
 result:=True;
    try
      OldErrorMode := SetErrorMode(SEM_FAILCRITICALERRORS);
      try
        AssignFile(fp,DriveLetter);
        Reset(fp);
        CloseFile(fp);
      finally
        SetErrorMode(OldErrorMode);
      end;
    except
      on E:EInOutError do
        if E.ErrorCode = 21 then
         result:=False;
     end;
  end;