The boot loader will pass default partition information to the booted operating system if this variable is omitted. It specifies the DOS drive letter for the partition that will be booted. The drive letter may be specified with or without a trailing colon. This keyword starts a section which describes how primary partition IDs are changed, and how primary partitions are activated and deactivated. In addition, partition 2, will be set normal, and activated.
Activation sets the boot-flag in the partition table.
This mapping is useful for booting operating systems, such as DOS, from the second hard drive. This disables some sanity checks, including a partition table check. This is useful to specify test kernels that are not always present. This is typically used to specify parameters of hardware that can't be entirely auto-detected or for which probing may be dangerous. The image will contain modules needed at boot time, such as network and scsi drivers.