https://qooah.com/2013/07/19/%e6%96%b0%e6%ac%be-nexus-7-%e8%a6%8f%e6%a0%bc%e8%b2%bc%e7%b4%99%e6%9b%9d%e5%85%89-4gb-ram%ef%bc%81%ef%bc%81/