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Bootable "Live" CDs: Description A "live" boot CD is one that boots from your optical drive and contains a full operating system. These boot CDs do not actually require a working hard drive: They work entirely off the optical drive, system memory (RAM disk), and video card. Well, of course, you need a working monitor and basic keyboard input at least. Despite not requiring a hard disk to "operate," live CDs can access hard drives, which is what makes them particularly useful. These days, boot DVDs are also common, but I will use "CD" for more universality.
In terms of user experience, live CDs can have very modern user interfaces that look and behave very much like current operating systems. Of course, due to the CD/RAM nature, live boot CDs have higher requirements than the simple DOS boot CD I host in another subsection. For the pretty user interface and RAMdisk to work, live boot CDs require quite a bit more RAM than a DOS disc—often 128MB minimum at default, and much more if it's a live DVD.
Nearly all live CDs, however, are Linux-based—but this does not necessarily mean one must be well-versed in Linux to use the live CD (as I write on another page about Knoppix for Windows users).
Purpose There are two primary reasons to use a bootable live CD: for data (or system) rescue and to "try out" an operating system without actually reformatting and installing it. A secondary purpose is giving the user access to their preferred and customized operating system and software on an otherwise disfavored operating system (e.g. using Linux software on a Windows PC or vice versa).
The best critical use for bootable live CDs is undoubtedly data rescue. If a virus renders the Windows operating system unusable, for example, a live CD can be used to read the otherwise inaccessible hard drive contents. Most current live CDs also support USB and networking, which in turn are useful to save the data elsewhere. In both corporate and personal settings, I've always found, the data is more important than the nuts and bolts of the computer.
Besides data rescue, a system may also be rescued from a live CD. In the above example, many current live CDs are bundled with antivirus and other malware tools and can scan and manipulate the hard drive contents. Such tools are limited to software problems, of course, and cannot fix something like faulty RAM.
Appropriate Audience Live CDs have evolved a great deal in the past half decade; while the earliest lacked eye-pleasing user interfaces and were either too customizable or too hard-coded, there are many to choose from now—perhaps too many, for average users.
In my opinion, users who wish to use live CDs in a rescue capacity should understand the basics of bootstrap media and how system memory, hard drive, and other component parts interact, particularly if the disc does not boot the system for some reason. Users who intend to use live CDs only for OS "trial" purposes need only know how to change media boot order in the CMOS, if at all.
For the most basic live CDs, where everything is already packaged and "ready to go," users must know how to burn images (ISOs or IMG or other) to disc. This is generally a straightforward and well-documented process. For other packages, the user needs to customize plugins or settings and compile (especially Linux-based CD distributions) before burning to CD.
Security Issues While the beneficial function I intend to highlight is data rescue for one's own computer, there is no denying that live CD use also effectly trounces the built-in Windows/NTFS protections such as user logons, NTFS folder/file permissions, and so forth. The fact that the BartPE and some other CD-ROMs can so easily access NTFS partitions (relevant particularly in business settings) and read data should make people hesitate. In terms of personal and corporate computers, the security issue is twofold:
- Physical access to the computer must be secured, perhaps even disabling any removable media on the computer.
- Bootable media must be secured via the BIOS/CMOS settings (i.e. disable or reorder bootable optical drive capability and secure the CMOS with a password).
Obviously, one can sometimes get around a CMOS password, but I suppose you might argue that once you give someone physical access to your computer, it's all over anyway. A more full-proof way to render these devices useless is to use full-disk encryption, which I may discuss in a separate QND article.
That said, here's my obligatory disclaimer: I take no responsibility for actions derived from the information on these pages that fall outside the intended use for personal emergency PC access.
