the booting behavior. These vary from distribution to distribution but can most often be accessed upon first boot screen by one of the function keys. Some live CDs come with an installation utility launchable from a desktop icon that can optionally install the system on a hard drive or USB flash drive. Most live CDs can access the information on internal and/or external hard drives, diskettes and USB flash drives. Live CDs are usually distributed on read-only media, requiring either copying to rewriteable media (i.e. a hard drive or CD writer) or complete remastering to install additional software; however, there are exceptions. If Puppy Linux is recorded to an open multisession medium, changes made during use (such as files created, programs installed, and preferences customised) are written in a new session to the boot medium persisting through subsequent boots. The term "Live CD" came to be used for any CD containing operating system and software which could be run without installation on the host computer. 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. There are maintenance versions of Microsoft Windows bootable from CD such as BartPE, Windows PE, and Microsoft Diagnostics and Recovery Toolset (DaRT), previously known as Emergency Repair Disk Commander (ERD Commander). The first personal computer operating system on a CD to support "live" operations might have been the AmigaOS, which could be booted from CD on an Amiga CDTV in 1990.. Earlier examples of live OS are of course the operating systems used from floppy, and most widely spread is DOS. Unlike previous operating systems on optical media, though, Linux and OS/2 "live CDs" were specifically designed to run without installation onto other media like a hard disk drive. 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. On a PC, a bootable Compact Disc generally conforms to the El Torito specification, introduced in 1994. Many Linux based live CDs use a compressed filesystem image, often with the cloop compressed loopback driver, or squashfs compressed filesystem, generally doubling effective storage capacity, although slowing application start up. The resulting environment can be quite