The latest version of Mac OS X, code named Lion, is now available, for a remarkably low price, from the OS X App Store.
But there's one thing that a lot of people don't know about it:
It removes support for a particular kind of old application.
Specifically, applications that were written to run on old PowerPC Macs, the kind that were made before Apple switched to using Intel chips, will no longer run.
They've continued to run on Intel Macs for the past few years due to a cool but invisible piece of Apple software called Rosetta, which translated between the old system and the new system.
But Rosetta won't run under Lion.
So if you're still using PowerPC applications, then you should get your data out of them and find replacements for the apps before you switch to Lion. Or else you should stick with Snow Leopard or other pre-Lion versions of Mac OS X.
Which applications are PowerPC apps? Well, MacWorld provides a way to find out. But the one that people seem to be most often still using is Quicken for Mac. Various replacement apps do run under Lion, though.
The other non-Lion app I wanted to specifically mention is Eudora, 'cause I know a couple of you were still using it last I heard.
Me, I migrated off of Eudora a couple years ago, but I still have ten years' worth of email in Eudora mailboxes, so I still open it up to search for stuff now and then.
So the time has finally come for me to clean things up and migrate all of my old mail out of Eudora.
But until I do that, I won't be upgrading to Lion.