https://purengom.com/2011/05/31/ipad-2%eb%a5%bc-%eb%b0%9b%ec%95%84%eb%93%a4%ea%b3%a0-%ea%b2%8c%ec%9e%84%ec%9d%84-%ed%95%98%ea%b3%a0%ec%84%9c-%eb%8b%8c%ed%85%90%eb%8f%84%ec%97%90%ea%b2%8c-%ec%a1%b0%ec%96%b8%ec%9d%84-%ed%95%98/