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Mount Rainier is a format for re-writable optical discs which provides for packet writing and defect management. Its goal is the replacement of the floppy disk. It is named after Mount Rainier, a volcano near Seattle, Washington, USA.

Mount Rainier (MRW) can be used only with drives that explicitly support it and works with standard CD-RW and DVD+RW media.

The physical format of MRW disks is an extension of the UDF format, but this is transparently managed internally by drive intelligence which remaps physical drive blocks into a virtual and defect-free space. Therefore the host computer does not see the physical format of the disk, giving it filesystem independence.

The time needed for the formatting of the disk is shortened to about one minute by the background formatting capabilities of the drive. Formatting allocates some sectors at the end of the disk for defect management. Defective sectors are recorded at a table in the lead-in (an administrative area) and in a copy of the table in the lead-out.

From the host computer's perspective, an MRW disc provides a defect-free block-accessible device, upon which any host supported filesystem may be written. Such filesystems may be FAT32, NTFS, etc., but the preferred format is usually UDF 1.02, as this file format is widely supported. An MRW-formatted CD-RW with a UDF filesystem gives approximately 500 MB free space.

Mt. Rainier allows write access to a disc within seconds after insertion and spin-up, even while a background formatting sequence is taking place. Before this technology, a user would have to wait for the formatting to complete before writing any data to a new disc. It is even possible to read (but not write) MRW disks without an MRW-compatible drive; A "remapper" device driver is needed, an example of which is EasyWrite Reader for Windows.

An alternative to MRW is to physically format a disc in UDF 1.5 or higher. This is achieved by the use of specialized packet writing software. MRW capabilities overlap somewhat with that of UDF 1.5+.

Advantages of MRW over UDF 1.5+

• fast background formatting of the media
• finer grained packet size of 2K versus 64K
• is file system independent
• does not depend on the host system to perform defect management

Advantage of UDF 1.5+ over MRW

• more portable, as it does not need specialized drive hardware to write

Mount Rainier is implemented natively in Windows Vista, which was released on January 30, 2007. Linux has built-in MRW support since kernel version 2.6.2 (2004). Amiga OS4 supports this natively since the first beta appeared in 2004. Operating systems that don't support MRW natively (notably Windows XP and prior versions) need third-party software to read and write MRW-formatted discs, and these tend to be the same packet writing utilities which allow native UDF filesystems to be written to optical media.

The EasyWrite logo is the marketing symbol for CD drives that are Mount Rainier compatible. The logo was created by Philips to ensure that products using the logo were tested and verified for quality.

CD-MRW stands for Compact Disc – Mount Rainier Read/Write.

• Homepage of the Mount Rainier standard (inactive)
• Mount Rainier Support in Linux
• Understanding CD-R & CD-RW by Hugh Bennett