Many older Macs lost out on the ability to run OS X Mountain Lion (10.8.3!), but some hard working fellows have created a free third party tool called MLPostFactor that allows for the newest version of OS X to be installed on older, officially unsupported Macs. The process used to be quite complicated, but with MLPostFactor it's easier than ever and can now be done by creating a partition, running the MLPF app, installing OS X as usual, then using the MLPostFactor app again to patch the 'failed' installation. Reboot and automagically OS X Mountain Lion will be running on the older Macs, breathing new life into older hardware.
This makes for an excellent weekend project, and if you're interested in trying this out yourself, review the compatible older Mac list to see if the machine you want to install is supported.
MLPostFactor Compatible Macs
- Mac released from 2006 to 2008 with Core 2 Duo CPU and Lion installed – PPC, Core Duo, and Core Solo chips are not supported
- MacBook late 2006, 2007, and 2008
- MacBook Air, mid 2007
- MacBook Pro late 2007 and mid 2007
- iMac 2006
- Mac Mini 2006
- Mac Pro 2006, 2007
- Xserve 2006, and early 2008
The requirements are basically such that if it supports Lion, it will now support Mountain Lion. Do note that some of the older Mac Pro and Xserve models have specific GPU requirements as well, so be sure to read the full MLPostFactor tutorial before beginning in order to determine if there is anything incompatible with the specific Mac model you are looking to install this on.
If you meet the requirements, you'll need to download the MLPostFactor app (link here), re-download Mountain Lion from the App Store, and, ideally, create a installer drive as if you were going to perform a clean install on a regular compatible Mac.
If your older Mac doesn't fit the compatibility list, don't feel too bad, but try out some tips to speed it up instead to breathe some new life into it. It won't be running a new OS, but at least it'll be a bit quicker.
Thanks to hackerwayne for the tip, and for creating MLPostFactor!