I usually choose according to the needs. At first, I would use an independent old computer to install MS-DOS for learning, but I found that it is not very portable. Because I am a computer student, so I installed MS-DOS on a USB flash drive. Then, more often, I still use virtual machines. Because in the current school computer lab, some MS-DOS games cannot be loaded into the high memory area (I am not skilled enough, a newbie, so I can't solve this problem). So when I get tired of learning MS-DOS, I will want to play MS-DOS games. So I will use the USB flash drive to boot the virtual machine and enter MS-DOS. This is the biggest advantage of the USB flash drive, strong portability. No matter on which computer, even in a virtual machine, you can operate your own files and your own saves.