贴个东西学习学习，哈哈

[wonderful]

摘自 "info grub"。

10 GRUB image files
*******************

GRUB consists of several images: two essential stages, optional stages
called "Stage 1.5", one image for bootable CD-ROM, and two network boot
images. Here is a short overview of them. *Note Internals::, for more
details.

`stage1'
This is an essential image used for booting up GRUB. Usually, this
is embedded in an MBR or the boot sector of a partition. Because a
PC boot sector is 512 bytes, the size of this image is exactly 512
bytes.

All `stage1' must do is to load Stage 2 or Stage 1.5 from a local
disk. Because of the size restriction, `stage1' encodes the
location of Stage 2 (or Stage 1.5) in a block list format, so it
never understand any filesystem structure.

`stage2'
This is the core image of GRUB. It does everything but booting up
itself. Usually, this is put in a filesystem, but that is not
required.

`e2fs_stage1_5'
`fat_stage1_5'
`ffs_stage1_5'
`jfs_stage1_5'
`minix_stage1_5'
`reiserfs_stage1_5'
`vstafs_stage1_5'
`xfs_stage1_5'
These are called "Stage 1.5", because they serve as a bridge
between `stage1' and `stage2', that is to say, Stage 1.5 is loaded
by Stage 1 and Stage 1.5 loads Stage 2. The difference between
`stage1' and `*_stage1_5' is that the former doesn't understand
any filesystem while the latter understands one filesystem (e.g.
`e2fs_stage1_5' understands ext2fs). So you can move the Stage 2
image to another location safely, even after GRUB has been
installed.

While Stage 2 cannot generally be embedded in a fixed area as the
size is so large, Stage 1.5 can be installed into the area right
after an MBR, or the boot loader area of a ReiserFS or a FFS.

`stage2_eltorito'
This is a boot image for CD-ROMs using the "no emulation mode" in
El Torito specification. This is identical to Stage 2, except that
this boots up without Stage 1 and sets up a special drive `(cd)'.

`nbgrub'
This is a network boot image for the Network Image Proposal used
by some network boot loaders, such as Etherboot. This is mostly
the same as Stage 2, but it also sets up a network and loads a
configuration file from the network.

`pxegrub'
This is another network boot image for the Preboot Execution
Environment used by several Netboot ROMs. This is identical to
`nbgrub', except for the format.

[zongweiming]

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