In order for a classic Mac to boot from a drive, there needs to be a System Folder. A system folder needs to contain the system file (aka system suitcase) and the Finder. Sometimes though, even if these files reside in a folder named “System Folder” the Mac still won’t boot – this is most likely because the folder isn’t “blessed”.
A blessed system folder is one marked by the Mac as a valid, bootable version of the System Folder. You can tell a System Folder is blessed when there is a small Mac system icon on the folder.
How to bless a System Folder
The easiest way, is to open the System Folder and double-click the system suitcase. This often is enough to indicate to the Mac that you want to use this as your System Folder.
Often times, simply copying the System file and Finder into a folder named “System Folder” should do the trick. A fresh install will also create a blessed folder.
Here’s a few more tips:
- You’ll confuse the Mac with multiple System Folders, or if you move a system suitcase into a different folder you can accidentally bless a different folder.
- You technically can have a system folder not named “System Folder”… but I wouldn’t recommend doing it… it’s a recipe for blinking “?” disk icons.
- Startup Disk will help you pick a drive to start from by default. These are drives with blessed system folders. The selection you make here is stored in PRAM which is persisted by the battery when power is off.
- There exists that allow you to mange multiple system folders on one drive such as System Switcher and System Picker
- Check out the Wikipedia article