After Apple dropped support for the first MacPro models I got seriously disillusioned with the company. After all I had plunked down a bundle back in 2006 to purchase an upgradable desktop computer.
The industry evolves and new HW creates a perpetual cycle of obsoleteness, I know this and have payed my dues. In this case the MacPro under my desk is more than adequate still, and just the fact that it does not support 64bit EFI boot should relegate it to the dump? Unacceptable.
So I just stopped upgrading and was stuck with Snow Leopard.
Then security updates stopped coming for Snow Leopard, and since I rely on Java and the Interwebz the situation became more and more troublesome.
Sure, there was the possibility to turn your MacPro into a Hackintosh, but I could never get that to work (apart from the fact that it sounds ridiculous to have to turn your Apple sanctioned product into a Hackintosh).
Before starting the process of selling a kidney to upgrade to a newer model, I did one last check on the internet and found How to upgrade MacPro1,1 to Mavericks
At first I couldn't believe what I was reading, but after downloading Mavericks and slapping it onto an old USB drive and patching the installer, it was true: my trusty old MacPro1,1 was running Mavericks.
I took the plunge and did an upgrade of Snow Leopard (which was on the original disk that came the Mac Pro and had been upgraded from Tiger and Panther and what have you). Unbelievably it worked.
Even though the original NVIDIA 7300 Graphics Card was way outdated and not supported, it also worked, albeit a bit slow since the CPU had to do all the work and shuffle huge swaths of memory back and forth (I guess), resulting in epilepsy inducing flicker.
After some research which Graphics Card to get and some wasted time on eBay (Mac Pro1,1 10.9.2 (Tiamo) Graphic Card Suggestions) I finally went to Fry's and got myself an ASUS NVIDIA GT-640 (regular PC version) and I haven't looked back. This old workhorse of mine has got some new life. Memory upgrade and SSD will follow.