MDF to ISO

The tool turns an Alcohol 120% disc image into a regular ISO. It reads the MDS descriptor along with the image: the descriptor names the tracks, their type, and their place in the file.

Why there are two files

MDF holds the sectors of the disc, and MDS is an inventory of them: how many tracks there are, what type each one is, and where each one starts. The MDF alone does not show any of this, so Alcohol and DAEMON Tools place two files with matching names side by side. The pair works the same way as BIN and CUE, except that the descriptor here is binary.

What happens during the conversion

A compact disc sector takes 2352 bytes, of which 2048 carry useful data; the rest is a sync word, a header, and error correction codes. ISO keeps only the useful part, so the resulting image is about 13% smaller than the original image. On a DVD, a sector is 2048 bytes to begin with, so the image is simply rewritten without changes.