My Mac SE/30 Part IX: System 7.5 Boot Floppy

In Part VIII of this series, I finished prepping a 2 GB SD card for the SCSI2SD that will serve as the primary disk for my vintage Macintosh SE/30. Now it’s time to get that disk formatted and a working system installed, but to do so I’ll need to create a boot floppy first.

As a quick recap, at this point I have a Macintosh SE/30 with a working floppy drive. I’ve installed 64 MB of RAM along with a GGLABS MACSIMM ROM replacement. I’m using the aforementioned SCSI2SD to simulate a single 1.75 GB hard drive, on which I intend to install System 7.5.5.

Formatting plan

The first thing I want to do is format that 1.75 GB drive with an HFS filesystem. The usual process is to boot from a floppy and use either the Apple HD SC Setup (for System 6) or Drive Setup (for System 7) program to format the drive. However, I’ve found that those programs don’t work well with the SCSI2SD. They don’t recognize the non-Apple drive by default, and even if you get a “patched” version which does, the resulting disk will have data corruption problems.

The solution is to use the third-party disk formatter Lido 7.5.6. It works perfectly fine with the SCSI2SD, however it doesn’t come preinstalled on a bootable floppy. So the actual first thing I need to do is to make a bootable floppy.

Creating the boot floppy

While there are many methods for doing this, I decided that since I’m planning on installing 7.5.5, that I wanted a 7.5.5 boot floppy. However by this time system CDs were becoming the norm, so the closest I could find was Apple’s System 7.5 Network Access Disk.

It’s provided as a disk image stored in a MacBinary-encoded self-extracting archive, so the first step is to download it onto a working classic mac and extract the disk image with Stuffit Expander. Then you can use the Disk Copy program to write the extracted “Network Access.image” file to a real floppy.

This is where having a bridge machine, like the Power Macintosh 8600/200 I previously restored, comes in handy. I could have easily done the whole process, from download to physical floppy, right there. But let’s assume for a moment that you don’t have a bridge machine, is it still possible to create a vintage mac boot floppy? Yes!

Note: Okay, technically, if your vintage mac only accepts 400/800k disks, then the answer is no. You’ll need a real, already working vintage mac to write one of these older floppies.

What you’ll need to do is create a bridge machine in emulation, with something like Mini vMac. To be honest, I use Mini vMac as a bridge machine way more often than I use my PowerMac. Other than the lack of networking and CDs, it covers most of my needs quite well.

Now, I’m not going to detail how to get Mini vMac set up. There are already plenty of tutorials out there for that and it’s worthwhile to get comfortable with the program before continuing. What I’ve got set up is a Macintosh II running System 7.5.5 with Stuffit Expander and Disk Copy (as above), along with the apps ImportFI and ExportFI to get files into and out of the emulator.

Creating a raw DSK image file

Without access to a real mac floppy drive, what we want is a raw DSK image of the Network Access disk. That is, we want a file with a 1-to-1 copy of the bits of that bootable floppy, without any extraneous headers or metadata. To start, we’ll need to use Mini vMac to get the Disk Copy image out of the archive:

  1. Download the Network_Access_Disk_7.5.sea.bin archive to your PC.
  2. Use ImportFI to import the archive file into Mini vMac.
  3. Use Stuffit Expander within Mini vMac to extract the archive’s contents.
  4. Use ExportFI to export the “Network Access.image” file out of Mini vMac back to your PC.

Now, the file we’ve exported is almost what we need. It’s a Disk Copy 4.2 image with all of the data we want, but it’s still wrapped up in some metadata we don’t. To strip that metadata we’re going to use a tool called Convert2Dsk.

Convert2Dsk is a small command-line tool I wrote to convert Disk Copy 4.2 images into raw DSK images on modern PCs. It works on Windows, OSX, and Linux, can even handle image files that are BinHex (.hqx) or MacBinary (.bin) encoded. Simply pass it an image file (or folder of image files) and it’ll convert them into DSK files.

On Windows, it’s as simple as dragging the “Network Access.image” file onto convert2dsk.exe, which will then create the “Network Access.image.dsk” file we want.

Writing the raw DSK image to a floppy

Now that we have a raw DSK image, it’s time to write that file to a floppy disk. Obviously that means you’ll need a floppy drive and at least one 1.4 MB floppy disk. You can get an external USB floppy drive on eBay, though a pro-tip is to avoid the new stuff from China, and instead pick up an older used drive made by one of the big PC manufacturers. They may cost a little more but they’re of higher quality and less likely to give you problems. I bought an old Dell floppy drive for $20 and it works perfectly.

Software-wise, you’re going to need a program to read and write the disk images, and I use dd (for Windows). It’s a powerful command-line utility for utility (also on OSX and Linux) for reading and writing directly to a drive by sectors. So from a command-prompt I’ll call dd.exe like so:

dd.exe if=<image file> od=<floppy drive letter> --progress

Which, with the file we created earlier, and my USB floppy registered as the A: drive, looks like:

dd.exe if="Network Access.image.dsk" od=a: --progress

Running with a floppy inserted will overwrite its entire contents with the contents of the DSK file. If you see “80+0 records in” and “80+0 records out”, then the write worked and the floppy is ready to use. Pop the disk into the SE/30, flip the switch, and… it doesn’t boot.

Fixing a 7.5 disk to boot a SE/30 with an upgraded ROM

It turns out that the combination of a SE/30 with the MACSIMM ROM replacement (which is based on the IIsi ROM) isn’t recognized by System 7.5 and above as a valid Macintosh computer. Thankfully this problem can be solved by making a minor patch to the system files, as detailed in this post: Mac SE/30 with Upgraded ROM.

However, I found that post to be a little overzealous in its instructions. Their goal is to setup a machine with each and every system version, using a tool called System Picker to let you switch between them. While it works, it’s a tedious process, and as I’ve stated, I only want System 7.5.5. So, simplifying their steps, here’s what I did in Mini vMac:

  1. Mount the raw DSK image as a floppy “Network Access.image.dsk” in Mini vMac.
  2. Use ResEdit to open the “System” file in the “System Folder” on the disk.
    1. Open the “gusd” resource.
    2. Open “ID 1”.
    3. Go to the 4th line (offset 000018) and change the end from 03 to 05. That is, the line should have changed from 0008 0003 0009 0003 to 0008 0003 0009 0005 as per below:
Modifying the System file in ResEdit
Modifying the System file in ResEdit
  1. Save and close the file.
  2. Eject the disk from Mini vMac.

Now if you write the modified disk image to a floppy using dd (as above), it should be bootable on the upgraded SE/30.

So that’s it, that’s how to create a System 7.5 boot floppy that will work on an SE/30 with an upgraded ROM. Stay tuned for Part X, where we’ll finally switch to the SE/30 and start setting up its disk drive.


Want to read from the beginning? Start at Part I.

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