主启动记录是指常驻在硬盘第一个扇区中的计算机代码，它包含有关该磁盘上磁盘分区的信息。
这个只跟硬盘有关，跟操作系统是什么没有关系。 主引导记录告诉机器从哪里启动系统，所以一般来说主分区是安装系统的。
This limitation is due to something called the Master Boot Record which tells the computer which partitions it can boot from, and so primary partitions are usually reserved for operating systems.
现在键入root (hd 0, 0)(或者是你自己得到的返回值)，以告诉Grub该从哪个分区启动，然后键入setup (hd0)以在你的硬盘主引导记录重新安装引导程序。
You should now type root (hd0, 0) (or your equivalent) to tell Grub which partition is being used to boot from, followed by setup (hd0) to reinstall the boot loader into the disk's master boot record.
这种现象称为链式加载(chain loading)，通常发生在位于主引导记录(MBR)中的引导管理器加载一个分区引导记录中的启动加载程序的时候。
This is called chain loading, and it most frequently occurs when the boot manager that is located in the master boot record (MBR) loads the boot loader that is in a partition boot record.
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