As Apple introduces newer versions of macOS, it means that older Macs are getting left behind due to aging hardware. This is kind of to be expected, and we expect that there are also some users who are choosing not to buy a new computer yet for whatever reason. This means that there are some who might be stuck using very old versions of a Mac operating system.
The good news is that Apple has since done away with the costs for its OS X Lion and Mountain Lion operating systems. Prior to this, Apple had charged customers $20 to upgrade to either OS, both of which were kept around and were targeted towards users whose computers couldn’t be upgraded beyond that.
Now it seems that upgrading to either version will be free, which is kind of in line with Apple’s approach to updates in the past few years where they’ve basically made all major Mac OS updates free of charge. Right now for those who wish to upgrade to OS X Lion, you would need to have a Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor, along with a minimum of 2GB RAM, and 7GB storage space.
As for OS X Mountain Lion, this is compatible with iMacs from 2007 to 2010, MacBooks from late 2008 or newer, MacBook Pro from mid/late 2007, MacBook Air from late 2008 and newer, Mac mini from early 2009 or newer, Mac Pro from early 2008 or newer, and Xserve from early 2009 or newer.