Shared Data Partition + Lion + Snow Leopard - What files go where?

That's going to be a problem. 😟

The file layout and/or folder structure for some apps is different, so Mail, for example, on the Lion partition won't be able to deal with a Snow Leopard setup -- it will try to convert the setup to Lion, and then Mail on Snow Leopard will be mystified.

Many apps will be fine, but you'll have to be careful in the future to update both. At some point, you may not be able to get compatible updates that will run on both Snow Leopard and Lion, and be in a similar pickle as above.

Most folks who have dual-boot situations do so because of one or two apps and/or hardware that only works on Snow Leopard, so they put everything for Lion on their Lion partition, and only what's necessary for Snow Leopard on that one.

I understand that you can run Snow Leopard as a Virtual Machine under Lion (or perhaps Mountain Lion). That might be a better option.

darkhorse85 wrote:

. . .

It would excellent if you would could me about other programs such as Mail which would suffer releated issues.

I really don't know, and don't know if there's a list anywhere of Mac apps. Mail seems to change with every release (and even some "point" updates). I think Calendar is one, too.

This list of 3rd-party apps is unofficial, but seems pretty reliable as far as what will run where: http://roaringapps.com/apps:table

As you'll see, it's mostly geared towards Lion vs. Mountain Lion (and in a few months, will be Mountain Lion and Mavericks).

You'll probably have to use some trial-and-error, and/or contact the makers of the apps you use.

I am not familiar with using any kind of software as a Virtual Machine how would this work?

I'm not very familiar with it, but you install 3rd-party software that lets you run one OS within a different one, rather than having to boot into one or the other. Basically, it puts a Virtual Machine folder containing one whole OS installation on the disk of another; it runs concurrently with the other OS, in a separate window (or multiple windows for different apps, I think). There are some downsides, especially performance, but a lot of folks do it, usually to run Windows, but some to run Snow Leopard on Lion or Mountain Lion. There may be some restrictions on the Snow Leopard license, too -- Apple didn't allow that for OSX at all for a long time, except for the Server product. I don't know what the rules are now.

Parallels and VMware are two I see mentioned often. I seem to recall reading about a free one, but as it's pretty complex software, I'm a bit skeptical.

I don't know where else to point you, but that should get you started on research. Look for those apps and/or Virtualization Software to find more.

Good luck!

Installing Snow Leopard into Parallels for use in Lion or Mt. Lion:

http://forums.macrumors.com/showthread.php?t=1365439

The entire drive has to erased and formatted GUID OS X Extended Journaled by Lion Disk Utility or Lion RecoveryHD's Disk Utility or via Internet Recovery to prepare it, the GUID, RecoveryHD and EFI for Lion compatability.

Once the drive is inside the machine and booting into Lion, then head to Disk Utility and create a second partition and give it a format OS X Extended Journaled.

Reboot the machine with the 10.6 disk (or USB thumb drive) holding the c or option/alt to boot from it and target the second internal partition to install OS X 10.6.

Quit and Reboot holding the option/alt key down to select the 10.6 partition and setup, then Software Update to 10.6.8.

You also can boot and erase/format the entire drive using the 10.6 disks, then Software update to 10.6.8, then create the second partition and use Carbon Copy Cloner to clone A to B, then boot from A and upgrade to Lion.

Keep the files you want to use in Snow Leopard in Snow Leopard partition.

Keep the files you want to use in Lion in the Lion partition.

Use a external drive to transfer files from Snow Leopard to Lion.

Cross compatability and/or a shared data partition will not work as Lion versions of programs will alter the Snow Leopard created files, so it's a one way street.

However some generic cross platform/operating system versions of files like jpg, mp3, .mov, .doc, .txt and so forth likely have no trouble crossing back and forth.

Apple is all forward and no backwards, once your files are altered by later OS X verisons and by their software, they are almost incompatible with earlier OS X versions.

Best to purchase the current version of Parallels, version 8 and it is very stable. Be sure to check for updates online once installed.

You can download a 14 day free trial from their website:

http://trial.parallels.com/index.php?lang=en&terr=us

Apple is now selling Snow Leopard Server for $19.99 + sales tax & shipping costs at 1.800.MYAPPLE (1.800.692.7753) - Apple Part Number: MC588Z/A (telephone orders USA & Canada only).

darkhorse85 wrote:

...And how reliable is it, I would be too keen on it crash and destroying an hours worth of design work.

Also: I always recommend that data files not be stored inside of Parallels but on the actual Mac that is hosting it.