现在我们可以说已经不再使用软驱了，所以当我们需要进入DOS界面时，需要进行一些在DOS下运行的程序软件时，就只有通过带启动功能的光盘来实现这一原来由软盘实现的功能。因此我们需要修改系统默认的启动项，将光驱设置为系统第一启动设备，这样才能保证系统启动后由首先读取光驱内光盘，由带启动功能的光盘引导进入DOS或启动界面。-Now we can no longer use the floppy drive, so when we need to enter the DOS interface, you need to carry out some program running under DOS software, it is only through the disc with a start function to achieve this original function by floppy . Therefore, we need to modify the system default startup items, the optical drive as the system boot device, so as to ensure that the system starts by first reads the disc in the optical drive inside, start function CD to boot into DOS or start interface.