Convert Mac CHDs Back and Forth into Other Formats

This document was created as an annex to several Mac related tutorials.

The aim of this document is to explain specifically how to convert MESS CHD files into Mac OS / Basilisk compliant files.

For users using Mac OS X 10.5 Leopard, these image files can be natively opened and modified by the system. Simply name the image to end in .dmg and double-click it in the Finder. When you are done working with the image, drag the drive icon to the Trash/Eject first to unmount it prior to converting it back to a CHD.

Unfortunately, Mac OS X 10.6 Snow Leopard removed native HFS support. It's possible earlier versions of OS X will also work for this but we have been unable to verify that.

It is possible to download read/write support for the HFS file system in Snow Leopard from here:


  • Format and read/write HFS partitions
  • Supports HFS file attributes and resource forks, of course
  • Automatically blesses a folder when you copy a valid System file into it


  • Mac OS X 10.6
  • MacFUSE 2.x


You will need some files prior to get into this tutorial

Working installation of MESS

… Or at least chdman

You can compile it from source using the following :

make chdman

Minimum Recommended Version is SVN Revision 9050 (or version 0.139u3 or later).

A MESS compatible Mac CHD

The image you'll use must have been created using mess and chdman (see this tutorial to see how, or to download already prepared images). In a second time, you'll be able to convert this image between MESS and Basilisk.

Note : Image created through other methods will usually lack the partition table and driver partition and will not work with MESS. MESS images, on the other hand, can be written block-wise out to a real HDD and will boot properly on a real vintage Mac.

BasiliskII Mac Emulator (Recommended), HFSExplorer or Mac OS X 10.5

The aim of this tutorial is to easily transfer files from your computer to your MESS CHD. To this end I use BasiliskII since it got a handy “sharing” function. Yet, you will need a working installation of BasiliskII with a functional OS in it.

As I said before, for the Mac OS X 10.5 Users, Leopard has read/write support for HFS images. Convert the CHD to an image as described below, then simply double-click the .dmg in the Finder and a drive icon will appear for the MESS image. You may then access the image as if it were any other drive. When you're done, be sure to drag the drive icon down to the trash/eject icon in the Dock.

HFSExplorer seems to be an alternative for getting things done, yet I can't test this method right now. Feel free to expand this part if you can.

How To...

  • Convert a MESS CHD into a suitable Mac OS X/ Basilisk drive image :

chdman extracthd -i messdrive.chd -o basiliskdrive.dmg

  • Convert a Basilisk image back into MESS CHD format :

chdman createhd -c none -i basiliskdrive.dmg -o messdrive.chd

Note that if you are using Mac OS X to access the image, you must drag the drive icon to the eject/trash first to unmount the image prior to running CHDMAN to convert to MESS format.

  • Or, if you prefer, you may use “createhd” without “-c none” to compress the CHD, in expense of speed :

chdman createhd -i basiliskdrive.dmg -o messdrive.chd

Here’s a set of already formatted and partitioned blank Mac hard disk images (.CHD). Big thanks goes to Grégoire Duval and Arbee.