这里转载一篇管OB的文章,很透彻:
http://www.cnblogs.com/zhenyulu/articles/641728.html
http://www.cnblogs.com/zhenyulu/articles/641743.html
http://www.cnblogs.com/zhenyulu/articles/641760.html
http://www.cnblogs.com/zhenyulu/articles/641767.html