Create Large (4GB > x > 20 MB) Mac CHDs

This is the second part of several mac related tutorials. The first part can be found here (Install Macintosh System 6) and here (Install Mac OS 7.5.3) is the third part.

Please note that you no longer have to do this part yourself! You can simply download pre-made blank formatted CHD images here from Arbee's site.


You will need some file prior to get into this tutorial

Working installation of Mess

Minimum Recommended Version is Revision 9050 (Some revisions after the 0139u2 milestone)

Working installation of System 6

Go to this page for more information

Original Apple HD SC Setup

Since the patched one fail at Initializing really big HDs, you must have the original Apple Tool found on the 2nd installation floppy of System 6 (see here for the detailed instructions)

Patched HD SC Setup

You need a patched version of the “Apple HD SC” tool since the original one will not work with bigger hard drives. You can get it here :

you can use "The Unarchiver" which is a tool for Mac and PC (as a beta under the name “unar”) to perform SEA Decompression.

At one point in this tutorial, you will have to copy a file from your real computer to an image. 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.

HFVExplorer 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.


  • Convert the chd into suitable Basilisk drive image :

chdman extracthd -i macsehd.chd -o macsehd.dmg

  • In Basilisk now, mount the macsehd.dmg and use the native sharing function to copy “HD SC Setup 7.3.5 (Patched)”
  • Convert back the Basilisk image to use it for MESS :

chdman createhd -c none -i macsehd.dmg -o macsehd.chd

Now You'll be able to format bigger drive images directly from your Mac SE.

First you need to create a new CHD using chdman. You have to use the right parameter for chdman how many Cylinders, Heads and Sectors you want. You can use this tool to figure out.

Note that depending on which OS you want to run, there is volume limitations. For instance, after System 6 and before System 7.5 the limitation is 2GB. Starting with 7.5 the limitation is raised up to 4GB.

You can use System 6 with >2GB HDs as long as you only format the drive on it, and don't actually use it. See here and there for more about HDs limitations under Mac OS.

IE : chdman createhd -c none -chs 8000,16,64 -o newmachd4gb.chd The result will be a 4GB Hard Drive image. Some another examples :

-chs 1400,16,64 : for a 700MB Hard Drive image

-chs 4000,16,64 : for a 2GB Hard Drive image

-chs 8000,16,64 : for a 4GB Hard Drive image (OS 7.5 only. see above)

  • Run MESS (or MESS64) with both drive images :

mess macse -hard1 macsehd.dmg -hard2 newmachd4gb.chd -ramsize 4M

  • Start “Apple HD SC Setup” (Not the patched one), keep pushing “Switch Disk” Until it reads “The disk is uninitialized …”
  • Click on “Initialize”, then on “Init”

If you have a fast forward key, just go for it

Wait …

  • Finally, name it like you want (MacHD4GB for me) and “Quit”

Last step is to make the whole disk enabled (at this time only some MB are usable)

  • Launch “HD SC Setup 7.3.5 (Patched)”, Keep pushing “Switch Disk” Until you get your new HD
  • Click “Update” then “Continue”
  • Click “Partition” then go “Custom”
  • Select your MacHD4GB partition and “Remove” it, “OK”.
  • Click somewhere in the gray box under “Mac Driver”, select “Macintosh Volume” then put the Maximum value into the box, then “OK”
  • “Quit” the application.
  • Turn off the mac (use the “Special” menu) and quit MESS.

You have now a valid CHD suitable for MESS, and that can be exported for use in Basilisk (Here for more about that).

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