应该是设置启动顺序时出现的吧，第一个从光盘启动，二从硬盘启动，三设备的意思。
1、Capabilities and management of a magneto-optical drive, a subtype of media access device.磁光驱动器媒体访问设备的一个分类的功能和管理。
2、The two-pound device had a seven-inch screen, no optical drive or hard drive, and occupied half the space of a typical notebook computer of the day.该设备，重2磅，配有7英寸屏幕，不带光驱和硬盘，而且所占空间只有如今标准笔记本电脑的一半。
3、Occasionally you will need to change the device boot priority to be able to boot a live Linux distro from your optical drive.有时你可能需要更改设备的启动优先级以便能够从光驱启动一个live版的Linxu发行版。