In protected mode a segment cannot be both writable and executable. Files are often copied to removable media such as writable CDs or cartridge tapes. These tables are readable and writable. PaX is supposed to guarantee that no RAM is both writable and executable. All converted files are available and writable in the default subvolume of the Btrfs. FlexClone is a licensed feature, used for creating writable copies of volumes, files or LUNs. A few computers were built using "writable microcode". Starting with the Pentium Pro in 1995, several x86 CPUs have writable Intel Microcode. To simulate immutability in an object, one may define properties as read-only (writable&colon; false). A multi-instance object may be writable or read-only, depending on what it represents. Each of the parameters may be marked as writable or non-writable. Writable snapshots were introduced with the LVM version 2 (LVM2). Writable objects allow dynamic creation and removal of their children. NFC tags contain data and are typically read-only, but may be writable. Pirate cartridges also often used writable chips instead of ROM.