N久不写东西了，总是以太忙为借口 ：（
Android中两个启动模式的不同点，解释的非常好
In a simple way-
singleTask:
The system creates a new task and instantiates the activity at the root of the new task. However, if an instance of the activity already exists in a separate task, the system routes the intent to the existing instance through a call to its onNewIntent() method, rather than creating a new instance. Only one instance of the activity can exist at a time.
Note: Although the activity starts in a new task, the Back button still returns the user to the previous activity.
singleInstance-
Same as "singleTask", except that the system doesn't launch any other activities into the task holding the instance. The activity is always the single and only member of its task; any activities started by this one open in a separate task.
来自：
http://stackoverflow.com/questions/3219726/android-singletask-or-singleinstance-launch-mode
