How to convert MDF to ISO, and why renaming fails
Windows mounts an ISO with a double-click but has no idea what to do with an MDF. The usual tip is to rename the file to .iso, and it often produces an image that will not open. To convert MDF to ISO properly you have to understand what is inside the file.
An MDF holds raw sectors read straight off a CD or DVD. Each 2,352-byte sector carries 2,048 bytes of actual data surrounded by 16 bytes of sync and address and 288 bytes of error correction. An ISO holds only the data. Renaming keeps all the extra bytes in place, so the file system lands at the wrong offsets and the image looks corrupt. Stripping those bytes from every sector is the real conversion, and it is why a 747 MB dump comes out at roughly 650 MB.
MDF2ISO does that stripping, but first it checks every file you add. It reads the sector headers, names the layout it finds, and reports how many sectors it holds, how big it is now and how big the ISO will be, all before a single byte is written.
The three MDF layouts it recognizes
Disc-imaging software can write an MDF in more than one way, and a converter that assumes one layout will silently ruin the others. Each file in the queue is labeled with what it actually is:
- Normal: 2,352-byte sectors, converted to a standard 2,048-byte-per-sector ISO.
- Bad-sector: 2,448-byte sectors with 96 bytes of subchannel data appended to each one.
- Audio: 2,448-byte sectors with no data area, from music CDs.
A single sector, drawn at true proportions
The main window shows a single sector stretched across it, in the true proportions of the layout that was detected. The bytes that survive into the ISO are lit and the ones discarded are hatched, so you can see at a glance where the size difference goes.
If a file is already a plain ISO 9660 image, it is flagged as such and left out, with a note suggesting a plain copy instead. A file whose headers match none of the three layouts is marked as not recognized and is not converted, rather than producing an output that only looks like success.
How to mount an MDF file in Windows after converting
Press Add a dump, pick one or more files, and check the layout each one reports. Then press Convert, or Convert followed by the number of files when there are several, and choose where each ISO should be saved. Progress is tracked per file, so a multi-gigabyte DVD dump never looks like a frozen window.
When the ISO is written, double-click it in File Explorer, or right-click and choose Mount, and Windows gives it a drive letter like a physical disc. If you set "When a dump is finished" to Open the folder it went to, the folder opens for you automatically.
