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May 21st

Mac Classic Target Disk Mode, Really.

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So you’ve got a Compact Mac (Plus*, SE, SE/30, Classic or Classic II), PowerBook 140-180c or Mac II era machine and an empty, or corrupted hard drive and no way to install system software except you have another Mac with a SCSI port.

Where I’m headed may send  shivers up people’s spines.. ;-)

If you have a working Macintosh capable of running the same system software you wish to install on whatever classic era system you are working with, this works really well, but if you’re using say, a 9600 to install 6.0.8 on an SE, you can do that too, with a few different steps.

If all you have are the two systems, with an internal hard drive, and equipped with an Interrupt Switch, or a work around and figuring you don’t have spare cabling/external cases around to temporarily connect a hard drive to another SCSI port or just don’t want to bother. :)

The Interrupt Switch is found on the lower rear left side of a Mac Plus, SE, SE/30, Classic, Classic II, lower right rear of a Mac II/x/fx, front lower left of a IIcx/ci or the rear panel of a Powerbook 140-180c. One switch resets, and the other interrupts. If you do not have one on those models where it’s removable, you can use a flat tooth pick with a flashlight to look into the vent holes where it would be. With the power off, you can find the switches, it will be the rear  most, or edge most one of the two.

If it’s a Plus, you pretty much can figure on an external SCSI drive unless it’s one of those where someone has installed one inside, or it’s one that’s not really a “Plus”, but using Levco, MacSnap, and other similar options to become a “Plus”, though here’s a Mac Plus with an internal hard drive being discussed on the 68K MLA forums.

Get a 25-25 pin SCSI cable. (Or other known full 25 pin conductor male-to-male straight through cable). Getting one that says “CMS” or some other known hard drive vendor pretty much assures you that the cable is what it is.

You will be using two Mac systems with SCSI ports, and on one of them you will need to verify that the SCSI id of  internal hard drive is not 6, and if it is, it’s probably a good idea to change it to something else and gratefully reduce the odds of having the two drives be the same ID since the default is 6, if they both shipped from Apple with the drive installed and have not been touched, it’s a pretty good bet that they both are the same.

Once you’ve changed ID’s, or otherwise decided to go for it and see if it works, connect the two machines together using the 25 pin SCSI cable.

Next you’ll want to turn on the Mac that you will be installing onto, this is the Target. As soon as the hard drive is spinning, and the screen displays something other than black, press the Interrupt Switch and wait 30 seconds. The display will usually turn black and display the black eye like icon. It may do something else, but as long as it’s not blinking a disk icon you’re good to go.

Turn on the host machine and boot as normal.

You should see an additional drive mounted on the desktop when you arrive there, or be prompted about an unformatted disk, or.. maybe nothing.

Launch your chosen formatting utility and see what you’ve got. You should see the Target machine’s HD in the SCSI ID list. If not, you’ve got an ID conflict, incorrect cabling inside of the Target machine, or a non-functioning drive within the Target machine.

Incorrect cabling encompasses everything from term power settings, resistors, disconnected power or data cables, etc.

Once you’ve got the drive connected and visible it’s just a matter of doing what you would normally do. Install your choice of system software and when it’s done, shut down the Host system, and then the Target system.

As mentioned earlier, if you’re installing system software that you can not run the installer on the host system, you’ll want to install a minimum system onto the Target machine. This can be as simple as just the contents of the chosen system’s “System Tools” floppy image. I recommend doing this in two steps. First being, copy the contents of the floppy and shut down, disconnect and boot that machine to verify that it’s working, sees that minimum system software, and the System Folder should have the Macintosh icon overlaid on it.

Once that’s verified, re-attach the system the way it was and copy over the entire System Software installer set you wish to use. If all you have are Floppy images, you may mount them individually, copy each of them to a folder that is the same name of each floppy, and put all of these folders into another one entitled “6.0.8 Install” or whatever you want to call it, and place anything else you want to install onto the hard drive while it’s mounted.

When you disconnect again, you can now use that system installer to finish the job on the Target machine. Older systems will allow you to install components while it’s the active system.

This article was inspired by an answer I submitted to a thread on MacInTouch, and I figured I’d go into a little more detail here.

Who’d have thought Apple actually had “Target Disk Mode” before we knew it :)