How To Load Multiple Mac OS's On A Mac
Most Mac users who have used a Mac for any length of time know how to do this, but many new users are not aware of the capabilities of running multiple Mac os's on a single Mac.
What OS Is Best
Some apps require 7.6 (internet mostly), otherwise there really is no need to run 7.6.x. I wouldn't run 8 on an 040 or PowerMac, I'd run 7.5.5 on the 040 and 8.6.1 on the PowerMac unless you have 64 megs of ram or more in which case I'd run 9.x. If you have a G3 with 256 megs or more, then X will run fine. As you can see, I see no reason to run 7.1 or 7.6 on any Mac. 7.5.3 is free as well as the upgrade to 7.5.5. Another advantage to running 7.5.3 or up is you don't have to worry about those pesky system enablers for 7.1. All the enablers are built into 7.5.3.
How Do I Dual Boot?
Easy. If you are loading an OS prior to 7.6, and you already have an OS on the drive, simply name the current system folder to something like '7.0.1 system folder'. Next, take the Finder file and hide in a new folder called Finder Folder. This 'unblesses' the system folder and allows you to do a normal install of say 7.5.5. This will create a new system folder called 'System Folder'. You can then rename this system folder to '7.5.5 System Folder'. Subsequently, to boot off the 7.0.1 system later, hide the finder in the 7.5.5 system folder and UNHIDE the finder in the 7.0.1 system folder. To unhide the finder, just drop it into the system folder 'naked' - without being in another folder.
If you are loading an OS 7.6 or up, you have an option for a clean install during the install process. This automatically renames the current system folder to 'Previous System Folder' and unblesses it, allowing you to load another OS in a new system folder. Some people will perform a 'dirty install' by loading say os 7.5.5 on top of 7.1 or 8.5 on top of 7.5.5. While Apple says this is OK, I DO NOT RECOMMEND IT. OS's that are years newer than your older OS don't know what some of the older files are and may leave them there, potentially mangling your OS. I have never done a dirty install in my life, but I know lots of people who have had trouble after performing a dirty install, so take it from me: DON'T DO IT!!
You can also use Apple's System Picker to choose the OS you want to boot off. I routinely keep 6.0.8, 7.0.1 and 7.5.5 on my Plus, 7.5.5, 8.6.1 and 9.1 on my 7500 and 8.6 and 9.1 on my iMac.
Tricks and Caveats
If you are using a Mac Plus and you change the system folder you wish to boot form, it may take a long time to rebuild the desktop. This rebuilding is normal and occurs on older OS's when you boot off another system folder. Download desktop manager to keep this from happening. This also works on other Macs.
Sometimes the Mac Finder file or System file will become damaged, either giving you a flashing question mark upon bootup, or just wreaking havoc and crashing your Mac constantly. For an easy fix, just keep a backup of your Finder and system on your hard drive and replace them with the backups as needed. To do this, you must move your current finder (the one that might be bad) into another folder. Next, drag the backup finder into the system folder 'naked'. Now you can safely throw away the bad finder. After you do this, you may need to re-bless your system folder by opening the system folder, then closing it, then opening and closing again. If the system folder icon doesn't look like the picture on this page, your system folder is not blessed and your Mac will not boot.
Do NOT replace your bad finder or system files with one off a Mac OS CD! These are NOT the same as the finder and system that are installed during the installation process. You'll create even more problems if you try this!
Every now and then, after copying very old programs from the 80's to my PowerMac hard drive for uploading to the web, I get an unblessed system folder. This is because some very old programs have system folder built into them from the days when these apps actually booted your Mac. This can create an unblessed system folder on your drive. The only way to remedy it is to hide the finder in these old system folders, or remove them completely and re-bless your system folder.
Do not put your backup copies of the finder and system in the same folder or your Mac with treat that folder as another system folder! Put them in separate folders. By the same token, don't keep multiple blessed system folders on your hard drive as it confuses the Mac and creates lots of problems. Always make sure you have only ONE blessed system folder.
A blessed system folder - this will boot the Mac.
An unblessed system folder will NOT boot a Mac, you'll get a flashing question mark on your screen.
The finder folder you created to hide the Finder
Here is what my Mac Plus systems look like:
Here is what my PowerMac systems look like:
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