A large number of computers that have appeared in recent years have been configured with UEFI BIOS, but most of them are started by Legacy BIOS by default. After the official launch of Win8, all computers pre-installed with Win8 (or Win8.1) are equipped with UEFI BIOS and both start the operating system by UEFI mode by default. UEFI is the trend of the times, but the situation of Legacy + UEFI coexistence may still need to last for a long time. So, whether you want to try UEFI boot on an old computer or want to switch a pre-installed Win8/8.1 system to another operating system, you should be familiar with the UEFI/Legacy BIOS switch method. Know how to do it, and it's best to know why. This article will take Lenovo's pre-installed Win8 computer as an example. Use Chinese and English picture comparison method combined with text description to explain each setting option and its meaning in the switching process. Different computers have different BIOS settings interfaces, but the options that need to be set are basically the same, but the options will change. The level of understanding is limited. If you have any mistakes, please do not hesitate to point out. ^_^ First, press the computer power button (or restart). When the system shuts down the computer and enters the restart process, press the shortcut key repeatedly to interrupt the computer to enter the BIOS setup interface. Note: Different computers have different shortcut keys to enter the BIOS, usually F1, F2, DEL, ESC, etc. The specific setting options are as follows: 1. The OS Optimized Defaults system default optimization settings are switched to the “EXIT” tab. As shown below (click to view the big picture, the same below) In some pre-installed Win8/8.1 computers, there will be OS Optimized Defaults option. Computers without pre-installed Win8/8.1 do not have this setting option. OS Optimized Defaults is a “top level” setting option. When this option is enabled, the BIOS will automatically restore all related options (ie each option described below) to the standard settings required for pre-installed Win8/8.1 default boot mode. . Specific settings: When switching to UEFI: If you only install Win8/8.1, you can select “Enable” and other situations “Disable”; when switching to Legacy: select “Disable”. . 2. The CSM compatible module settings are switched to the "Startup" tab. The CSM (Compatibility Support Module) is a compatible module. This option is designed to be compatible with devices that can only work in legacy mode and operating systems that do not support or do not fully support UEFI. For example, many of the discrete graphics cards currently do not have GOP BIOS support and cannot work normally in UEFI mode. In this case, you must “Enable” and “CSM”. It should be noted that the CSM option and the secure boot (described below) conflict on a computer configured with Class 2 UEFI, and only one of them can be turned on at the same time. The specific settings are as follows: When switching to UEFI: It is recommended to select “Disable” under the condition that Win8/8.1 is installed and need to start safe boot. In other cases, select “Enable” and “Switch to Legacy”. : Select “Enable”. 3, Boot Mode startup mode Select this option is still in the "Startup" “ tab, Boot Mode (boot mode), this is the main setting option to switch UEFI /Legacy BIOS. There are generally three options: Auto: Automatically start in the order of the boot device list, with UEFI mode first; UEFI only (UEFI only): Select only devices with UEFI boot conditions to start; Legacy only (Legacy only): Select the device with the Legacy boot condition to start; select one as needed. 4. Secure Boot Secure Boot Setup Secure boot is an optional standard for UEFI (it is invalid in Legacy mode, no need to be set). This option is not available on some UEFI computers. A motherboard with a secure boot can be built with some reliable public key. Only the software (system) signed with the corresponding private key can be loaded by the authentication of the built-in public key during the startup process. Malware cannot be certified and naturally cannot be loaded. Therefore, this will ensure that the computer is safe to boot. UEFI does not specify the specific issuer of the public key. On pre-installed Win8/8.1 computers, Microsoft forces OEMs to adopt the secure boot standard and place Microsoft's own public key. The pre-installed Win8/8.1 computer is safely booted by default to the “Enable” status, which results in the inability to boot other operating systems including Win7 by default (currently, the existing system can pass the authentication), but The user can choose to turn it off. Switch to the Security tab, as shown below and then open the secure boot option settings, as shown below; there are two options: the first, the Secure boot option. If we want to install a system other than Win8/8.1 in UEFI mode, you must choose to shut down. In addition, you need to pay attention to the conflict between the CSM and the secure boot mentioned in the CSM option settings above. In view of the times, we usually set it to “Disable”, and in the off state, there is no need to consider the second setting option. Second, reset to the Reset to Setup Mode/Restore Factory Keys option. This option is used to clear or restore the built-in secure boot key. Generally we do not need to set this option. If your computer is pre-installed with Win8/8.1, you have changed the relevant settings options, and now want to restore the default settings (including turning on secure boot), you can use this option to restore the key to the default.