Debian Live マニュアル　日本語版

3.1. live systemとは

A live system usually means an OS booted on a computer from a
removable support (as CD-ROM, USB stick, or network), ready to
use without any installation on the usual drive(s), with an
auto-configuration done at runtime (see Section 1.1.1, ?Terms?).

With Debian Live, it's a Debian GNU/Linux OS, built for one of
the supported architectures (currently amd64, i386, powerpc and
sparc). It is made from following parts:

Linux kernel

The Linux image, usually named vmlinuz*.

Initial RAM disk image (initrd)

RAM disk setup for the Linux boot, containing modules possibly needed to mount the filesystem's image and some scripts to do it.

System image

The O.S. image. Debian Live uses a SquashFS image, a compressed filesystem, to minimize its size. Note that it's read-only, so during boot, the Debian Live system will uses RAM disk and 'union' mechanism to be able to write files on the system, but all modifications will be lost when shutdown, until using optional persistence partition(s) (see Section 7.5, ?Persistence?).

Bootloader

A small piece of code, crafted to boot up from the chosen media, possibly proposing a prompt or menu to let select options/configuration, then loading the Linux kernel and its initrd to let it run with associated filesystem image. Different solutions can be proposed depending of the target media and format of filesystem containing the previous components: Isolinux to boot from a CD or DVD in ISO9660 format, syslinux for HDD or USB drive boot from a VFAT partition, GRUB for ext2/3 partition, pxelinux for PXE netboot...

The Debian Live tools will build the system image from your
specifications, setup a Linux kernel and its initrd, a
bootloader to run them, all in one media-dependant format
(ISO9660 image, disk image, ...).