The term ISO Disk Image File Format is used to name a range of variants that are not governed by a single comprehensive specification. In addition to the ISO 9660 and UDF types identified above, the structure for an ISO disk image may employ extensions like the Rock Ridge Interchange Protocol, an IEEE standard that supports the preservation of POSIX (Unix-style) permissions and longer names; the Joliet filesystem specified by Microsoft that supports names stored in Unicode, thus allowing almost any character to be used, even from non-Latin scripts; El Torito, which enables CDs to be bootable on PCs; and Apple ISO 9660 Extensions, which add support for Mac-OS-specific file characteristics. Tools and operating systems offer varying support for these extensions; in some cases the media-independent entity may not be fully system independent. Comments welcome that clarify the impact of the use of these extensions on long-term data management.