通知中心
Notification Center was added in the operating system. It provides an overview of alerts from applications and displays notifications until the user completes an associated action, rather than requiring instant resolution. Users may choose what applications appear in Notification Center, and how they are handled. There are three types of notifications: banners, alerts, and badges. Banners are displayed for a short period of time in the upper right corner of the Mac's screen, and then slide off to the right. The icon of the application is displayed on the left side of the banner, while the message from the application will be displayed on the right side. Alerts are the same as banners, but will not disappear from the screen until the user takes action. Badges are red notification icons that are displayed on the application's icon. They indicate the number of items available for the application.