there are also several ways to switch between dual systems and set the default startup of the system. Press the Option key when starting the machine. This method is the most used method and the most commonly used method. This is actually very simple, that is, after booting, keep pressing the Option key until the system selection interface appears, press the left and right arrow keys to select the system we need to start, and then click with the left mouse button directly or press Enter to confirm. Some points to pay attention to. 1。 The time when the Option key was pressed. Apple officials and websites basically use the phrase "hold down the Option button when turning on the phone", and rarely specify when it is most appropriate to press this button. In fact, users who have used Apple for a period of time will have some such experiences. Sometimes we haven't pressed the Option key, and it has entered the system by default. Or sometimes we press it for a long time, only to find that the screen has been in a gray state. In both cases, it is basically because we pressed the Option key late. When this happens, we can only restart it or turn off the power button and then restart it. There are also some users who are new to Mac, and they don't have an idea about how long this Option key will be pressed. They think that it is enough to press it once, and it is not enough to let go when it is turned on. Generally speaking, the best time to press the Option key is after pressing the power button, when the boot sound comes to mind, press the Option key immediately when the gray screen appears on the screen, and then let go until the system startup selection interface appears. For notebook users or users who use wired keyboards, this is actually very simple. We just need to hold down the Option key, and then press the power button to boot until the system startup selection interface appears. Users who use iMac actually need some skills, because iMac comes standard with a wireless keyboard. Before the system is started, the keyboard and the computer have not been connected directly, so it is useless to press the Option key at this time, but if you press it late, it will easily lead to staying in the gray screen interface or directly entering the system. Therefore, users of iMac system should grasp the time of pressing the Option key as mentioned above. 2。 Set the system to be started by default. When starting, start the selection interface. In addition to selecting the system we need to start, we can also set the system we need to start by default in this interface. The selection interface for startup is as follows