glob *.chd, application/x-mame-chd

Was originally developed by MAME, as HDD and CDROM media started appearing on the arcade machines turning up for emulation. As an in-house developed product catering for specific needs, there aren't of course too much documentation around. Even the name is doused in obscurity with the mime type referring to "Compressed Hard Drive" but that is not what others say.

Basically it is a compressed block device with LBA support which has had some time to mature. It originally had cylinders, heads, and sectors which evolved into maps and hunks as the technology matures heading towards a 6th itteration. It has both compressed (read-only) and uncompressed (read-write) support with the MAME emulator implementing COW (copy on write) for transparent write-ability while maintaining the integrity of the original dumps.

With the help of Libretro, part of the bigger RetroArch project, assisting with the development of the new rtissera/libchdr library, has seen CHD gaining new popularity as more and more emulators are starting to adopt the format and old ROM sets are getting converted.

The only thing that is missing now is how to mount your CHMs, which reminded me, cdemu is the place to go for all things mountable and then some.

Hoping this peaked some interests =)