1. Legacy BIOS, UEFI, MBR, GPT
1.1 Legacy BIOS
BIOS (Basic Input Output System) is a program stored in the motherboard chip, which saves the computer's most important basic input and output programs, power-on self-test programs and system self-starting programs.
1.2 UEFI
UEFI (Unified Extensible Firmware Interface, the same extensible firmware interface) replaces the traditional BIOS.
1.3 Hard disk partition initialization format
1.3.1MBR format
MBR (Master Boot Record) is a traditional partition table type.
The disadvantage of the MBR partition format is that it does not support hard drives with a capacity greater than 2T, and the BIOS only supports MBR boot systems.
1.3.2 GPT
GPT (GUID Partition Table, Globally Unique Identification Partition Table), a new disk system partition format, makes up for the shortcomings of MBR and is based on the disk partition architecture used by UEFI.
1.4 How to choose the method to boot the system and the format of the hard disk partition?
1.4.1 BIOS boot + MBR partition
The traditional method is supported by all systems. The disadvantage is that it does not support hard drives with a capacity exceeding 2T.
1.4.2 BIOS boot + GPT partition
The BIOS can use a GPT partitioned hard disk as a data disk, but it cannot boot the system. You must choose a hard disk smaller than 2T and use the MBR partition table to install the system
1.4.3 UEFI boot + MBR partition
UEFI can be set to Legacy mode to support traditional MBR boot, which is equivalent to BIOS + MBR. Common modification items are:
1）将Secure Boot Control改为Disabled，表示禁用安全启动，一定不要忘记！！！
2）将Lanch CSM修改为Enabled，表示兼容模式
3）将Boot mode或UEFI mode或Boot List Option改为Legacy，表示传统启动方式
4）OS Optimized Defaults改为Disabled或Other OS，表示禁用默认系统优先显示
1.4.4 UEFI boot + GPT partition
If the system disk is larger than 2T, this method must be used, and the system must be 64-bit.
2. BIOS boot + MBR partition
2.1 Use EasyBCD software to create system USB disk
Similar to using micro PE to make a system disk, this software is used as a system boot and saves the Ubuntu18.04 system image file to a USB drive.
Software download address: EasyBCD
2.2 Create a blank disk partition under Windows 10
Select the last disk (for example, the computer has a CDE disk, and the last one is the E disk) and allocate a part of the space (for example, 200G)
2.3 Install Ubuntu18.04
It should be noted that the Linux partition is different from the Windows partition. Assuming that the free partition separated from the last disk is 100G, the partition is:
1）/boot：这个是实现双系统的原因，这个是用于启动Ubuntu的目录，里面会有系统的引导文件（几十兆），建议划分200M，格式为ext4
2）swap：这个是Ubuntu的交换区目录，大小一般为内存的2倍左右，用于在电脑内存不足时，系统会调用这部分区域来运行程序
3）/：这个就是Ubuntu的根目录，相当于Windows的C盘，软件默认是装在这里的
4）/home：这个是Ubuntu的其他盘，相当于Windows的D盘
Note that you find the corresponding number in the drop-down menu of the installation startup. This number is the number of the area where the /boot file was created.
Because the system boots in the /boot partition, you need to use EasyBCD to create a system for it to choose whether the system is Windows or Ubuntu when starting up. Otherwise, it will enter Windows directly by default and there is no option. Open this software and select the option starting with linux in the disk drive drop-down menu (the size is about 200M).
2.4 Dual hard drive installation
Note that when creating a blank disk partition under Windows, it is the last disk of the last hard disk, and everything else is the same.
3. UEFI boot + GPT partition
3.1 Use micro PE to make system USB disk
Write Ubuntu18.04 system image file to USB flash drive
3.2 Create a blank disk partition under Windows 10
Still select the last disk
3.3 Install Ubuntu18.04
3.3.1 It is recommended to install the system without connecting to the Internet.
3.3.2Linux system partition
Linux is partitioned by files. Partitioning is similar to dividing the disk size:
1）efi：这个就是实现双系统的原因，这个就是用于启动Ubuntu的目录，里面会有系统的引导文件（几十兆），建议为其划分200M左右，格式为efi
2）swap：这个是Ubuntu的交换区目录，大小一般为内存的2倍左右，用于在电脑内存不足时，系统会调用这部分区域来运行程序
3）/：这个就是Ubuntu的根目录，相当于Windows的C盘，软件默认是装在这里的
4）/home：这个是Ubuntu的其他盘，相当于Windows的D盘
It should be noted that you can find the corresponding number in the drop-down menu of the installation startup. This number is the number of the area where the efi file was created. The startup item of the Windows system is also an efi file, which is about 500M in size. The boot file of the Ubuntu system created is about 200M. Be sure to choose the right one!
3.4 Dual hard drive installation
When creating a blank disk partition under Windows, note that it is the last disk of the last hard disk, and 200M of space needs to be allocated on the C drive to install the startup items. The startup items are installed on the first disk, and will be installed on the first disk when entering the system later. There is no need to select Ubuntu to start from the boot, which is more convenient.
4. The interface freezes during startup due to the graphics card driver.
You can enter the Ubuntu advanced options, select recovery mode, then select grub, and then select resume to enter the system, but this only temporarily solves the problem.
Permanent solution: Modify the /etc/default/grub file, change quiet splash to quit splash nomodeset, save and exit editing; then enter sudo update-grub in the middle to update the file. Reference link: Ubuntu dual system freezes during startup