The most important function of iPhoneOS4.0 is that it supports long-expected multi-task operation
. When you use multi-task operation, only by clicking Home key, you can open other programs and you can also use multi-task operation in the case of the keyboard lock. In iPhone OS 4.0, users can directly open the attachments in Emails through programs; this design seems more practical for users. Due to the popularity of e-books, Apple also released its own iBooks. At present, Apple iPad is the only product that has iBooks. The release of iPhone OS4.0 will enable iPhone and iPod Touch to support iBooks. Meanwhile, users can synchronize bookmarks and page numbers through the Internet on a cross-platform.