Mount Rainier or MRW is an extension to the Universal Disk Format (UDF) which is intended to replace the floppy disk as a "swappable" media. Mount Rainier is used on DVD+RW and CD-RW re-writable media.
Unlike UDF, Mount Rainier is completely hardware-based, and operating system independent. Mount Rainier also includes hardware defect management and background formatting, which enables users to access a new disc immediately upon insertion.
Mount Rainier was named after the volcano in Seattle, Washington.
Mount Rainier is now implemented natively in Vista, Linux and OSX but is notably missing in Windows XP. There are no operating systems used before 2004 that have support and you will need a third-party software to read and write MRW-formatted discs.