Universal Disk Format (UDF) is a CD-ROM and DVD file system standard developed as a means of ensuring consistency among data written to various optical media, by facilitating both data interchange and the implementation of the ISO/IEC 13346 standard. UDF is required for DVD-ROMs, and is used by DVD to contain MPEG audio/video streams. Originally developed as a replacement for the file system specifications in the original CD-ROM standard, ISO 9660, UDF is used by CD-R and CD-RW in a process called packet writing that makes CD writing more efficient in terms of the time and disk space required.
The Optical Storage Technology Association (OSTA) defines the UDF specification as a subset of ISO/IEC 13346, which it promotes as a single file system that overcomes limitations of ISO 9660 and redirectors such as CDFS. UDF is used to ensure compatibility across platforms, as well as among various CD and DVD applications.