rich: typical Knoppix systems include around 1,200 separate software packages. Live CDs have a reputation for supporting advanced auto-configuration and plug-and-play functionality. This came out of necessity to avoid requiring the user to configure the system each time it boots and to make it easily usable by those who are new to the operating system. Creation A read-only file system, such as on a CD-ROM has the drawback of being unable to save any current working data. For this reason, a read-only file system is often merged with a temporary writable file system in the form of a RAM disk. Often the default Linux directories "/home" (containing users' personal files and configuration files) and "/var" (containing variable data) are kept in ramdisk, because the system updates them frequently. Puppy Linux and some other live CDs allow a configuration and added files to be written and used in later sessions. In modern live CDs, a read-only file system is merged with a RAM drive using transparent techniques such as UnionFS, AuFS or EWF. Boot loaders like syslinux can boot ISO files from USB memory devices. Live CDs have to be able to detect and use a wide variety of hardware (including network cards, graphic cards etc.) 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. See also Boot disk Comparison of Linux distributions#Live media GIS Live DVD List of live CDs List of remastering software Live USB Self-booting diskette Software appliance Windows To Go References External links Bootable CDROM HowTo Linux Live scripts Pondering Live CDs - A BSD perspective on the concept of Live CDs Software appliances