Way back in 2008, @JDW pointed out the following article in which an unnamed init could enable a stock-ROM SE/30 to mount an HD20 hard drive (or Floppy EMU emulating an HD20).
web.archive.org
"Additionally, we have included an INIT Utility that reads the data from the
Hard Disk 20 and puts it on the internal hard disk of the Macintosh SE/30. As
with all INITs, place it in the System Folder of the startup disk. The Hard
Disk 20 will now be visible when you start up with the Hard Disk 20 turned on."
This init is different than the well known HD20 init that first enabled HFS and the ability to boot an HD20 on the Macintosh 512K.
Fast forward to this week (2025), @SuperPete suggested the unnamed init is "MacIIHD20" (attached) from the Developer CD Series 1990: Night of the Living Disc.
Guess what? It works:
I have confirmed that a factory System 6.0.3 floppy disk with the MacIIHD20 init permits mounting a Floppy EMU HD20 on a Macintosh II, IIx, IIcx, and SE/30. This is particularly nice when servicing cap-goo Macintosh II computers, as they do not have ROMinator-style replacement ROMs.
Issues:
1. Thus far, I have been unable to mount standard 1.44 MB floppies after booting with the init enabled. The init hails from June 1987, prior to FDHD drives.
2. Thus far, I have been unable to get it to work in newer versions of System 6. I was successful in having it work when booting in 7.1 from a hard drive on a Macintosh IIx. So, there's hope.
3. The Macintosh IIfx crashes in each attempt I've made (factory System 6.0.5 or 6.0.8 floppy disk with the MacIIHD20 init). I suspect this is due to hardware differences. This is disappointing because it would help to have an HD20 volume when fixing up battery-bombed IIfx computers.
Below are the contents of the read me file, written by a very worried Apple developer.
- David
Macintosh II HD-20 Support
6/5/87
Warning:
This software is not supported. Additionally, the hardware and even the manual (this document) is not supported. It is not a product, and is to be used at the risk of the user. Caveat Emptor!
!
Macintosh II HD-20 Support
! Warning:
Since the Macintosh II internal IWM port is not buffered (as external IWM ports are in other Macintosh products); there exists a real danger of causing severe damage to the IWM itself when installing. Taking the precautions recommended here minimizes the risk of this happening, however some damage may still occur since the Macintosh II was not designed to support the HD-20. Please read all of this document before even attempting to install any of the hardware. The greatest danger is in installation and removal. At the very least, please keep the number of times that you install/remove this hardware to a bare minimum
!
Installation:
¥ Turn both the Macintosh II and the HD-20 off. This step is paramount in avoiding costly repairs to both machines.
¥ Remove the cover of the Macintosh II.
¥ Touch the power supply in an effort to remove static electricity from your body.
¥ Remove the floppy drive cable (if your MacII is so equipped) from the internal IWM port #2 (the connector nearest to the NuBus slots).
¥ Connect the ribbon cable to the IWM port #2.
¥ Feed the ribbon cable out the rear of the machine (through an open slot access port).
¥ Replace the cover on your Macintosh II.
¥ Remove the screw and top cover of your HD-20.
¥ Touch the power supply in an effort to remove static electricity from your body.
¥ Remove the cable coming into the HD-20 at the 20 pin connector (this looks amazingly like the Macintosh II's IWM port connector).
¥ Connect the ribbon cable to the 20 pin connector inside the HD-20.
¥ Leave the HD-20 in a position where it will be least likely to cause accidental eloctrocution and where the fan is least likely to get external objects (your fingers) in it.
¥ Turn on the HD-20. (continued on next page)
¥ Turn on the Macintosh II.
¥ After booting the Macintosh II, insert the floppy drive to drive #1 (located at the far right hand side of your Mac II) and copy the file "MacIIHD20" to your system folder.
¥ Select "Restart" from the Special Menu.
Your Macintosh II will now reboot mounting the HD-20. You are now in a position to copy data from the HD-20.
!Recommendation:
Since this software is RAM-based, it is slower than the normal floppy disk driver. You are also at risk of damaging your computer when you install the hardware affiliated with this software. It is the recommendation of the author that you use this software as it was intended, to retrieve data from your HD-20 and place it on a different storage media. Nothing prevents you from using it in an "extended" fashion, except that you are running a risk and there was not enough time to properly trim the execution loops of the driver. I recommend against it.
!
After copying your data from the HD-20, you should remove it to guard against the possibility of an accidental electrocution, damage to your computer equipment, or both.
Removal:
¥ Remove the file "MacIIHD20" from your system folder.
! Warning:
This software must be removed from the system folder prior to disconnecting the HD-20. Failure to do so will require booting off an alternate system and removing the file "MacIIHD20" from your original system folder while under the alternate system.
!
¥ Turn off your Macintosh II and your HD-20.
¥ Touch the power supply of the HD-20 in an effort to remove static electricity from your body.
¥ Remove the ribbon cable from the 20 pin connector.
¥ Replace the original cable for the HD-20, replace the cover and secure it with the screw that you previously removed.
¥ Remove the cover of your Macintosh II.
¥ Touch the power supply in an effort to remove static electricity from your body. (continued on next page)
¥ Remove the ribbon cable from the IWM port #2 connector and remove the ribbon cable from the computer.
¥ Replace the cable from floppy drive #2 (if so equipped) into the IWM port.
¥ Replace the cover on your Macintosh II.
This completes the removal process.
Use:
The use of this software or hardware voids all warranties on your HD-20 and Macintosh II. Once it is in place, you may use the HD-20 as you would normally, realizing that not enough time to properly modify the driver has been given. You will experience especially long waiting times should you choose to write to the HD-20.
! Warning:
Do not connect an external floppy drive to the pass through connector of the HD-20. This software does not support such configurations. Additionally, the hardware does not support older single sided drives from the IWM port. Failure to comply will bring unexpected results.
!
You may however connect another HD-20 to the pass through connector of the HD-20. The additional HD-20 will operate as does the first.
Configuration:
You will need to have at least the following equipment. A Macintosh II equipped with a viedo card, monitor, ADB mouse, and a SCSI hard disk. This hard disk must have a system folder on it and be the "boot" system. An HD-20 in operating condition. A ribbon cable (20 conductor) with keyed "L" connectors on each end exactly with the same keying as the floppy cables inside the Macintosh II. Appropriate tools for removing the covers of both the Macintosh II and the HD-20.
AppleCare Document: 6182
web.archive.org
"Additionally, we have included an INIT Utility that reads the data from the
Hard Disk 20 and puts it on the internal hard disk of the Macintosh SE/30. As
with all INITs, place it in the System Folder of the startup disk. The Hard
Disk 20 will now be visible when you start up with the Hard Disk 20 turned on."
This init is different than the well known HD20 init that first enabled HFS and the ability to boot an HD20 on the Macintosh 512K.
Fast forward to this week (2025), @SuperPete suggested the unnamed init is "MacIIHD20" (attached) from the Developer CD Series 1990: Night of the Living Disc.
Guess what? It works:
I have confirmed that a factory System 6.0.3 floppy disk with the MacIIHD20 init permits mounting a Floppy EMU HD20 on a Macintosh II, IIx, IIcx, and SE/30. This is particularly nice when servicing cap-goo Macintosh II computers, as they do not have ROMinator-style replacement ROMs.
Issues:
1. Thus far, I have been unable to mount standard 1.44 MB floppies after booting with the init enabled. The init hails from June 1987, prior to FDHD drives.
2. Thus far, I have been unable to get it to work in newer versions of System 6. I was successful in having it work when booting in 7.1 from a hard drive on a Macintosh IIx. So, there's hope.
3. The Macintosh IIfx crashes in each attempt I've made (factory System 6.0.5 or 6.0.8 floppy disk with the MacIIHD20 init). I suspect this is due to hardware differences. This is disappointing because it would help to have an HD20 volume when fixing up battery-bombed IIfx computers.
Below are the contents of the read me file, written by a very worried Apple developer.
- David
Macintosh II HD-20 Support
6/5/87
Warning:
This software is not supported. Additionally, the hardware and even the manual (this document) is not supported. It is not a product, and is to be used at the risk of the user. Caveat Emptor!
!
Macintosh II HD-20 Support
! Warning:
Since the Macintosh II internal IWM port is not buffered (as external IWM ports are in other Macintosh products); there exists a real danger of causing severe damage to the IWM itself when installing. Taking the precautions recommended here minimizes the risk of this happening, however some damage may still occur since the Macintosh II was not designed to support the HD-20. Please read all of this document before even attempting to install any of the hardware. The greatest danger is in installation and removal. At the very least, please keep the number of times that you install/remove this hardware to a bare minimum
!
Installation:
¥ Turn both the Macintosh II and the HD-20 off. This step is paramount in avoiding costly repairs to both machines.
¥ Remove the cover of the Macintosh II.
¥ Touch the power supply in an effort to remove static electricity from your body.
¥ Remove the floppy drive cable (if your MacII is so equipped) from the internal IWM port #2 (the connector nearest to the NuBus slots).
¥ Connect the ribbon cable to the IWM port #2.
¥ Feed the ribbon cable out the rear of the machine (through an open slot access port).
¥ Replace the cover on your Macintosh II.
¥ Remove the screw and top cover of your HD-20.
¥ Touch the power supply in an effort to remove static electricity from your body.
¥ Remove the cable coming into the HD-20 at the 20 pin connector (this looks amazingly like the Macintosh II's IWM port connector).
¥ Connect the ribbon cable to the 20 pin connector inside the HD-20.
¥ Leave the HD-20 in a position where it will be least likely to cause accidental eloctrocution and where the fan is least likely to get external objects (your fingers) in it.
¥ Turn on the HD-20. (continued on next page)
¥ Turn on the Macintosh II.
¥ After booting the Macintosh II, insert the floppy drive to drive #1 (located at the far right hand side of your Mac II) and copy the file "MacIIHD20" to your system folder.
¥ Select "Restart" from the Special Menu.
Your Macintosh II will now reboot mounting the HD-20. You are now in a position to copy data from the HD-20.
!Recommendation:
Since this software is RAM-based, it is slower than the normal floppy disk driver. You are also at risk of damaging your computer when you install the hardware affiliated with this software. It is the recommendation of the author that you use this software as it was intended, to retrieve data from your HD-20 and place it on a different storage media. Nothing prevents you from using it in an "extended" fashion, except that you are running a risk and there was not enough time to properly trim the execution loops of the driver. I recommend against it.
!
After copying your data from the HD-20, you should remove it to guard against the possibility of an accidental electrocution, damage to your computer equipment, or both.
Removal:
¥ Remove the file "MacIIHD20" from your system folder.
! Warning:
This software must be removed from the system folder prior to disconnecting the HD-20. Failure to do so will require booting off an alternate system and removing the file "MacIIHD20" from your original system folder while under the alternate system.
!
¥ Turn off your Macintosh II and your HD-20.
¥ Touch the power supply of the HD-20 in an effort to remove static electricity from your body.
¥ Remove the ribbon cable from the 20 pin connector.
¥ Replace the original cable for the HD-20, replace the cover and secure it with the screw that you previously removed.
¥ Remove the cover of your Macintosh II.
¥ Touch the power supply in an effort to remove static electricity from your body. (continued on next page)
¥ Remove the ribbon cable from the IWM port #2 connector and remove the ribbon cable from the computer.
¥ Replace the cable from floppy drive #2 (if so equipped) into the IWM port.
¥ Replace the cover on your Macintosh II.
This completes the removal process.
Use:
The use of this software or hardware voids all warranties on your HD-20 and Macintosh II. Once it is in place, you may use the HD-20 as you would normally, realizing that not enough time to properly modify the driver has been given. You will experience especially long waiting times should you choose to write to the HD-20.
! Warning:
Do not connect an external floppy drive to the pass through connector of the HD-20. This software does not support such configurations. Additionally, the hardware does not support older single sided drives from the IWM port. Failure to comply will bring unexpected results.
!
You may however connect another HD-20 to the pass through connector of the HD-20. The additional HD-20 will operate as does the first.
Configuration:
You will need to have at least the following equipment. A Macintosh II equipped with a viedo card, monitor, ADB mouse, and a SCSI hard disk. This hard disk must have a system folder on it and be the "boot" system. An HD-20 in operating condition. A ribbon cable (20 conductor) with keyed "L" connectors on each end exactly with the same keying as the floppy cables inside the Macintosh II. Appropriate tools for removing the covers of both the Macintosh II and the HD-20.
