[Macworld]

Post your comments for One Mac, two versions of OS X here

[DCJ001]

And there is one more option. You could make sure that you have a backup of your Snow Leopard boot drive, partition your internal drive, restore from your backup on one partition, then install Mountain lion on the other partition. Then you have both operating systems on the one hard drive.

[Endorphinity]

And yet another option, which is actually even simpler and faster than the one suggested by DCJ101 above: if you have enough free space on your hard disk, you can simply launch Disk Utility, select your hard drive, go to the Partition tab and resize your existing partition. After that, you can add a new partition, where Mountain Lion can be installed. As simple and cheap (=free) as that.

[JMHammer]

My mid-2007 20" iMac has a smallish 55gb partition on which I keep 10.5 Leopard to run older software requiring Rosetta or other older OS components. I find that Leopard experiences fewer compatibility issues than 10.6 Snow Leopard with the really old software, and since I boot into it this partition so infrequently I don't mind that it isn't as secure or otherwise modern as Snow Leopard. Besides, I still have a late-2003 15" PowerBook G4 running Leopard and it continues to be useful when I need it.

My main partition of about 445gb runs 10.8 Mountain Lion, which runs much better than 10.7 Lion and I think better than Snow Leopard, too. If your Mac can run Lion but can't run Mountain Lion, you should run Snow Leopard unless you need something specific in Lion that Snow Leopard can't do; I never like Lion much. But if your Mac can run Mountain Lion, there's almost no reason not to do so as your main OS unless you absolutely need Rosetta frequently.

[mexikoplatz]

Why does Apple prohibit virtualization of Snow Leopard but not Snow Leopard Server?

[wingsy]

A while back VMWare Fusion had a version that supported Snow Leopard under Lion. I use that to run Snow Leopard for one PowerPC app that I still need. Not sure if that version also supports Mountain Lion ... probably not, but you may want to look into it.

[LeTap]

I often swap startup between Snow Leopard (SL) and Mountain Lion (ML), and even though ML was installed over SL, every time I boot up in SL it resets my finder window views, which I then have to set up all over again in ML.

[revco]

>The other option is to run Mountain Lion in a virtual environment…<

That's been my only experience of ML and it works fine for me.

[Goldie01]

@Endorphinity

You and DJC001 are essentially saying the same thing. Making a back-up of your Snow Leopard partition before resizing it and creating a new partition for Mountain Lion is the more advisable course of action.

[JustinB]

I'm in rough the same position. What I did was to partition my 1TB Firewire 800 portable hard drive using iPartition, then do a clean install of Mountain Lion. Obviously it was a little slow at times, so I'm going to try and partition my HD and put it on there instead. If it all works smoothly I'd like to then delete my current OS of Lion and be left with only Mountain Lion.

But I can definitely vouch for the external hard drive installation method. I've done it before a few times with older versions of OSX.

[anotherfahlman]

According to Mountain Lion's licensing agreement (http://images.apple....docs/OSX108.pdf) it can only be virtualized on Mountain Lion. It can not be virtualized on another version of Mac OS X.

(iii) to install, use and run up to two (2) additional copies or instances of the Apple Software within virtual operating system environments on each Mac Computer you own or control that is already running the Apple Software, for purposes of: (a) software development; ( testing during software development; © using OS X Server; or (d) personal, non-commercial use.

[Milliways2]

I have a MacBook Pro (early 2011) originally Snow Leopard, which I have repartitioned and installed Lion, and Mountain Lion. Incidentally, this was easy, did not require backup and restore - although I did later need to do so to move a partition. I use Mountain Lion almost exclusively, and only reboot to the others to test software.

My reading of the Apple licence agreement is that I could legally install Snow Leopard in a VM on Mountain Lion while I still have Snow Leopard on this machine. If I needed to run it more often I would try this.

[FernandoJofreAlfonso]

And what if I have Mountain Lion in a MBA (it came with Lion) and want Snow Leopard? Can it be done? How? (I´d like to buy the DVD with SL that are currently selling in the Apple Store)

[AMCarter3]

I have the same issue... I have a new (mid-2012) MBPro and need to use a legacy software program that will run on Snow Leopard, but not on Lion or Mtn Lion.

A senior Apple Tech person told me Snow Leopard cannot be installed on my laptop due to hardware limitations. He said there are 3 options: 1) VM ware solutions - create a partition and emulate older hardware; 2) Buy an older computer that can run Snow Leopard; and 3) run SL on an external USB hard drive. I have not done any of this yet and am very interested in hearing more success stories.