Snow Leopard on 10.7+ Mac
Hello and welcome to my User Tip.
Why run Snow Leopard? To use older PPC processor based software that there are no Intel versions or because you like a slim fast operating system or the older features etc.
If you Mac came from the factory with Lion 10.7. 10.8 or later OS X versions installed
The firmware will not let you boot from the 10.6 disk, nor are there hardware drivers for most Mac's later to run Snow Leopard. However you can install Snow Leopard Server into a virtual machine program legally and run that to run your PPC based programs, albeit a performance loss on demanding apps.
https://www.youtube.com/watch?v=9zjXaVtfkX0
This link explains what a virtual machine is : Windows in BootCamp or Virtual Machine?
If you have another 10.6 capable Mac and the target one is capable of running 10.6 just the firmware blocks booting from the disk, and both are Firewire Target Disk Mode capable, you can either create a combined 10.6.3 + 10.6.8 combo image or use Carbon Copy Cloner to clone the OS X 10.6.8 from one machine to the other.
The 10.6.8 combo update contains all the hardware drivers for the machine capable of running 10.6 regardless of the firmware setting, so it will have to be applied to the target machine before it will boot.
This old thread explains all the complexities involved: https://discussions.apple.com/thread/3264421?start=0&tstart=0
If you rather prefer to revert your entire Mac back to Snow Leopard after upgrading to 10.7 or later.
How to revert your Mac to Snow Leopard
If your machine already had Snow Leopard before and want to install 10.6 alongside 10.7 or later.
And if you have space space available at the bottom of your boot hard drive (SSD if you have enough space) and you have the 10.6 installer disks, then you can create a bootable Snow Leopard partition on the machine, provided BootCamp/Windows hasn't taken it yet.
If you don't have a clear space at the bottom of your boot drive, you can make it so with this procedure.
BootCamp: "This disc can not be partitioned/impossible to move files."
How to safely defrag a Mac's hard drive
If you don't have the 10.6 disks, then you can research this user tip about getting the correct 10.6 disks and if the 10.6 white ones will work for you or not.
If you don't know if your Mac had or is capable of running the Snow Leopard you can use the free MacTracker to find out and see the link above also.
All Intel processor Mac's to Early 2011 can run Snow Leopard, the Mac's to when OS X Lion was released (June 2011) can run Snow Leopard and for some time afterwards can be "shoehorned" onto certain factory 10.7 issued Mac's.
Procedure for partition install of Snow Leopard on firmware capable machines
1: First backup your users files and make a bootable clone of your present OS X drive. This is bootable and you can use it to repair, erase and reverse clone if something messes up. Disconnect it once the clone is made and booted (hold option/alt key down on a wired/built in keyboard and boot up) to verify.
Most commonly used backup methods
2: Open Disk Utility click on your boot drive and the partition tab. Attempt to create a second partition below your main OS X one and notice the size it will allow, if it's not good enough for your needs (like you need more of the available free space) then exit without applying the change.
See this user tip then return.
BootCamp: "This disc can not be partitioned/impossible to move files."
How to safely defrag a Mac's hard drive
3: If you have a hard drive, use the Disk Utility > Erase Free Space > Zero (move slider one spot to the right) on the boot drive and wait for it to complete, it will map off any bad sectors that will prevent formatting or installing of OS X Snow Leopard. SSD's no need to do this.
4: Once you have created a second partition below your first one (named: "Snow Kitty"), you want to change it's format to OS X Extended Journaled and apply.
5: Next is the fun part, you follow these instructions below to install Snow Leopard (+ Rosetta for PPC apps), but you apply them to the Snow Kitty partition and you DON'T erase the entire drive or you will lose Mountain Lion partitions as well etc.
So just install OS X 10.6 into the "Snow Kitty" partition (or whatever you named it)
How to erase and install Snow Leopard 10.6
7: To boot into Snow Leopard or Lion you hold the option/alt key down for Startup Manager and select which one you want.
If your always in Snow Leopard or the other Lion, you can set either as a Startup Disk in System Preferences and it will tell the firmware which one to boot from so no need to hold the option key down.
6: Optionally you apply the software tweaks and such here to maximize Snow Leopard performance