https://blog.faceutil.com/2017/05/06/%ec%8b%9c%ec%8a%a4%ed%85%9c%ed%99%9c%ec%84%b1-%ed%8c%8c%ed%8b%b0%ec%85%98-%eb%b0%94%ea%be%b8%ea%b8%b0-bootmgr-%eb%b6%80%ed%8a%b8-%eb%a7%a4%eb%8b%88%ec%a0%80-%ea%b5%ac%ec%84%b1%ec%8b%9c-%e3%89%b2/