System Services is a singleton class to gather all available information about a device. Over 75 methods to determine everything from: System uptime, Network Information, Battery Usage, Accelerometer Data, Disk Usage, Running Processes, Memory Usage, and a complete UDID replacement based on unchanging device information.
打开连接:http://www.binpress.com/app/ios-system-services/1144
连接2: http://www.cnblogs.com/YouXianMing/p/3570954.html
原文：http://www.cnblogs.com/huntaiji/p/4014325.html