The concept behind Web caches is not new.Web browsers have long used cache to retain recently downloaded Web pages so that if the user returns to those sites,the browser only needs to reload those components on the page that have changed.

• 网站缓存背后的概念不是新的，网站浏览器早就采用缓存来保留最新下载的网站页面，因而用户如若返回到这些站点，浏览器只需重新加载页面上已经变了的部分。