A perennial topic of discussion amongst Mac system administrators is which operating system should be deployed to which Mac. There is a mountain of misinformation floating around the community and the Internet on this topic. Here, I hope to set a few things straight.
On any particular Mac, the earliest version of OS X supported by Apple is the version that shipped with the Mac in question. Installing an earlier version of OS X will either fail to install, fail to boot after installation, or cause unexpected issues after boot. Regardless of how well the install goes or whether or not the computer boots, Apple will not support this configuration. Answers to support requests will generally amount to “install the correct operating system”. See the link below for Apple’s notes on this topic and a list of which OS X versions shipped with each Mac computer (note, as of this writing, the chart has not been updated to include 2013 iMac models).
An Open Secret
It is widely held in the Mac sysadmin community that once Apple releases a new version of OS X, this new version includes the software components necessary to support the new OS X version on earlier hardware.
There are two situations in which this generally applies.
- An OS X installation that has had an update applied bearing the suffix “(Combo)”, as in “OS X Mountain Lion Update v10.8.5 (Combo)”, will usually support all hardware released prior to the update that meets the system requirements for the major OS X release, OS X Mountain Lion v10.8 in this example.
- The apps “Install Mac OS X Lion.app”, “Install OS X Mountain Lion.app” and soon, “Install OS X Mavericks.app”, from the Mac App Store will install OS X on any Mac computer released prior the latest update to the OS X installer app used.
I call this an “open secret” because you will find nothing in Apple’s documentation to support this claim, however it is generally correct. I say “generally correct”, because occasionally it isn’t, particularly when hardware and OS X releases come close together.
The only 100% certain way to ensure an OS X installation is appropriate for and supported on a Mac computer is to use the OS X installer supplied by Apple for the computer in question, which includes a factory-installed Recovery System (Recovery HD) and OS X Internet Recovery. See the link below for Apple’s explanation of OS X Recovery:
OS X Hacking
There are those in the community who, for various reasons, hack new releases of OS X, and insert components from the new release into a previous release in an effort to run an earlier operating system than Apple intended or supports on a particular Mac. The people doing this are clever and deserving of “geek cred”, but I would never recommend using such a hacked distribution in a production environment.
Running a “hacked operating system” may run afoul of the organization’s operating rules either self-imposed or legally required. Even in the absence of such restrictions, my recommendation stands. Vendor support is a key component in service level agreements. If you choose to deploy an OS with unsupported modifications, you are ultimately personally responsible for every system failure. This is not a position I want to be in or that I recommend you place yourself in.