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What is the oldest OS I can run on my Color Classic?

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Hi folks...


I have a Color Classic Mystic.  It has the 640 X 480 screen mod.  I have a LC 575 board installed and running the full 68040 processor in it.  I have a SCSI2CF card in it divided into four "hard drives".  I believe each drive is 2 GBs.  I tried to install a early version of 7 and it would not load.  I can load and run 7.6.1 and 8.1.  I would like to run the earliest OS I can on it. 


Is it possible to re format one of my "hard drives" with out messing up the other two hard drives (I guess partition is the proper way to describe it) ?  I spent so much time adding files and getting the internet up and running that I really do not want to format the SD card and start all over again.


Advice appreciated,





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Thank you History and erichelgeson for your help! 


As I was about ready to install 7.1, I found that I had formatted (partitioned) my SD card into three (not four as I thought) "drives"  Each drive is 4.8 to 4.9 GBs large. 

I also recall that one format type is for "younger" classic OSs and another type of format works for "older" (7.1?) OSs. 


I have down loaded the System enabler 401.  I have bought the original Mac Color Classic install disks, and they have just arrived!  I am about ready to install.  But now I see that my "hard drive" is about 4.8 GBs large.


I have yet to shove a floppy in the drive to start because I fear that I might screw something up.  Do I need to reformat this one partition into something smaller than 4.9 GBs?  And can I do this to this one partition with out screwing up my other two (8.1 and 7.6.1) partitions?  It took me a long time to get networking working on both 7.6 and 8.1 and I do not want to do all of that over again.  Also I have my software on 7.6 and 8.1 installed and configured just the way I like it.


Thank you both for the great advice and help,











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Posted (edited)

I believe anything before 7.5.2 has a maximum partition size of 2GB for the boot drive so it will likely not see your much larger partition. There are conflicting reports on this, though. If you have a SCSI2SD I'd try breaking one of your 4.8GB partitions into two, one of which is smaller than 2GB. 


See this thread for more content on this: 


Edited by ttb
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I had posted an article on Reddit about this very thing. 68040 Macs have a version of SCSI manager that can handle larger disks, but still can’t boot from >2GB. PCI PowerMacs introduced changes to the SCSI manager that allows for larger disks, where you likely get the “7.5.2” change you mention (PCI Macs required 7.5.2 minimum. 

Here’s the text as copied from my Reddit:


Pro Tip: Using large SCSI hard drives in old Macintosh machines (including Ultra 160 and Ultra 320)


I purchased a PowerMac 8600 that included a 4GB hard drive. The drive died. When I removed it I discovered a special adapter board and the drive was not 50 pin SCSI. The drive was actually a U160 drive with a SCA 80 to SCSI 50 pin adapter. 


In the aftermath I discovered this whole new realm of SCSI. And the inexpensive large drives that are in it. 


I found a lot of 4 Quantum Ultra 160 drives 18GB on eBay for $25 US including shipping. That’s about $7 a drive. 


I tried to format one. I ended up killing it. Now down to 3. 


Classic Mac OS is old. Dealing with drives this big requires special considerations. 


To save yourself some time, here’s a brief rundown of my experience on a 68040 Mac running System 7.6.1. 


FWB Hard Disk Toolkit 3.0 is your friend here. The driver for the drive along with the first partition must exist in the first 2GB of the drive. 

Easy solution:  Use Autoformat to format the drive as a single volume. Then unmount. Set drive to not AutoMount and resize it to 10240 bytes (10MB).


Create a 1.9GB or smaller partition for your OS. Then create another partition of the remaining drive space. 

Boom!  You can now boot older System 7 versions on a real SCSI drive on an 68k Mac with tons of GB of free drive space, using inexpensive decommissioned server drives. 


YMMV regarding drive compatibility. I’m currently buying several brands and models and sizes to try on various old Macs and I plan on building a nice vintage Mac SCSI drive compatibility table for everyone to reference. 

Yes I know about SCSI2SD. I’m more of a purist. Plus, I think this is more compatible and it’s far, far cheaper. 34GB drives are under $25 USD and the adapter boards are about $13.

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