Live CD
A live CD allows users to run an operating system for any purpose without installing it or making any changes to the computer's configuration.
The Tails operating system is aimed at preserving privacy and anonymity of its users, allowing them to work with sensitive documents without leaving a record on a computer's hard drive.
After the introduction of the audio compact disc, it was adapted for use as a medium for storing and distributing large amounts of computer data.
Early examples of operating systems which could be booted directly from CD-ROM are the FM Towns OS,[3] and the Desktop-VMS distribution of VMS, both of which were first released in 1989.
[4][5] Although early developers and users of distributions built on top of the Linux kernel could take advantage of cheap optical disks and rapidly declining prices of CD drives for personal computers, the Linux distribution CDs or "distros" were generally treated as a collection of installation packages that would first need to be permanently installed to hard disks on the target machine.
This was a new and different situation for Linux than other operating systems, because the updates/upgrades were being released so quickly, different distributions and versions were being offered online, and especially because users were burning their own CDs.
The first Linux-based 'Live CD' was Yggdrasil Linux first released in beta form 1992~1993 (ceased production in 1995), though in practice its functionality was hampered due to the low throughput of contemporary CD-ROM drives.
A few additional uses include: Several live CDs are dedicated to specific type of applications according to the requirements of thematic user communities.
These CDs are tailored to the needs of the applications in subject including general knowledge, tutorial, specifications and trial data too.
This allows developers to avoid the complexities involved in supporting multiple incompatible virtual machine images formats and focus on the lowest common denominator instead.
Typically after booting the machine from the live CD, the appliance either runs in non-persistent demo mode or installs itself, at the user's request, to an available storage device.
Operating systems which can be used live include AmigaOS 4, Amithlon, AROS, FreeBSD, FreeDOS, classic Mac OS, macOS, Microsoft Windows installation and repair discs, OS/2, ReactOS, NetBSD, OpenBSD, MINIX 3, Plan 9 from Bell Labs, MorphOS, OpenSolaris, BeleniX and others based on Solaris.
The live CD concept was meant to promote Linux and showcase the abilities of the free, open source operating system on conventional personal computers with Microsoft Windows already installed.
[citation needed] On a PC, a bootable Compact Disc generally conforms to the El Torito specification, introduced in 1994.
In modern live CDs, a read-only file system is merged with a RAM drive using transparent techniques such as UnionFS, AuFS or EWF.
in realtime, often using facilities such as udev, hotplug, hal, udisk etc.. which are a common part of all distributions based on Linux kernel 2.6.
