An MDF file is a disc image file, often associated with Alcohol 120%, a disc imaging and burning software. It's essentially a complete copy of a physical CD, DVD, or Blu-ray disc, stored as a single file. This image contains all the data, file structure, and properties of the original disc, including boot sectors, file systems, and any copy protection mechanisms. MDF files are typically used for backing up optical discs, creating virtual drives, and distributing software or games. They are often accompanied by an MDS file, which contains metadata about the disc image, such as layer break information for dual-layer DVDs. Using an MDF file allows users to access the contents of a disc without needing the physical disc itself, which is convenient for portability and preventing damage to the original disc. The MDF format is proprietary, but several software applications support mounting and extracting its contents.