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The Macintosh Plus SCSI Implementation Background The Mac Plus differed from the Macs that came before it in that it had a SCSI bus built in, and could boot from connected SCSI devices. This was fantastic for the time, even with hard drives of only about 20MB, considering that each floppy was a maximum of 800KB. At the time, the drives pretty much just worked, but that was because most of them came from Apple themselves, and were configured especially for their computers. Fast forward 3 decades, and those mechanical hard drives have all started to fail - electronically, physically, and so forth. Floppy drives can be easy to repair and get working again, but the media they use is becoming more and more scarce every day. Thankfully there are SCSI drive emulators that can present SCSI "devices" to these old macs to boot from - RaSCSI, ZuluSCSI, BlueSCSI, and so on. However, there are some caveats with getting these to work on the Mac Plus in particular, and I have never seen this documented ALL IN ONE PLACE - so here goes. The Problem: The Mac plus had a handful of SCSI issues right from the initial release, and there were at least three ROM releases to address these. Without going into too much technical detail, Apple did finally make things right... ish. There were still problems with the SCSI implementation that can make booting off of many modern SCSI to SD emulators tricky. Solution 1: Use a known good HD image made specifically for the Plus Short story: Images made specifically for the Plus have been constructed in such a way as to allow for the peculiarities of this system - formatting, HD drivers, etc. This may or may not be absolutely necessary, but it can't hurt. It is IMPORTANT to note that hard drive images made with some emulators WILL NOT WORK. Basilisk II seems to be the one that can be made to work. Solution 2: Configure the BlueSCSI (and others) specifically for the Plus This fix is documented, but difficult to find if, like me, you just jumped right in and didn't exhaustively read every single bit of documentation on these adapters. The below works on BlueSCSI (confirmed by me), and SHOULD work on others - but I have no experience with them. Place the below code snippet into a file in the root of your SD card, and name it "bluescsi.ini". This should make the BlueSCSI compatible with the Macintosh Plus.
[SCSI]
Some combination of Solution 1 and Solution 2 might be required - so if one doesn't work, try the other. Bonus info The Mac Plus has no internal pin header for SCSI devices, so an external device is your only option outside of floppies. The Plus also does not provide termination power from the bus, so your external device MUST be powered on its own. Not a problem for actual spinning hard drives, but everyone expects to power their SCSI to SD adapter from the bus itself. You could modify your Plus to provide power, but I had zero interest in doing this. |