Mac Pro 1,1 (2007) Not Updating To El Capitan I recently purchased an old Mac Pro, from eBay to use it as an advanced CPU performance computer as opposed to my 2012 MacBook Air that can't endure much. So far it is working, I have gotten a wireless dongle to connect, and I thought all was good until I went to my App Store to upgrade to El Capitan. When I click &quot;Get&quot; on it's page. I get this error:

We could not complete your purchase.
This version of OS X 10.11 cannot be installed on this computer.

I checked the Apple Upgrade page and it is all good. A quick look at the forms, still all good. Even a Google search on other locations on the internet did not help me. So, I have decided to present your ever so luxurious minds with my preposterous issue. I was wondering if any of you knew how to get my Macintosh to update. Is there some stupid mistake I am missing, is it seemingly unfixable? If you need my computer specifications, here they are:

Processor:  2 x 2.66 GHz Dual-Core Intel Xeon
Memory:  4 GB 667 MHz DDR2 FB-DIMM
Graphics:  NVIDIA GeForce 7300 GT 256 MB
Software:  Mac OS X Lion 10.7.5 (11G63)

Thank you for your efforts in advance.
Firstly: putting your serial number up for all to see may not be the best idea.

Your Mac Pro is an original Mac Pro. This means that it is not compatible with El Cap by default (I'll explain more later.) So yes, there's an error on your part.

Your MacBook Air is also (sadly) likely about as powerful as that Mac Pro. If you upgrade it, it's possible that you may find a different story, but regardless, that Mac is reaching end-of-life. Depending on your use case, it may be fine to upgrade it, but there's not a lot you can do. Instead, I'd recommend that you save up for either a more powerful PC or Mac.

With that said, you can make your Mac Pro work on El Cap if you really want to. It's a little tricky, but possible.

Your Mac is incompatible because it has a 32-bit EFI firmware and an outdated GPU. Both of these are fixable issues. I would recommend reading this article, but I'll summarize here. By using a different bootloader, you can circumvent issues. Follow the instructions on said page. Your GPU is also unsupported. This means you'll need a new GPU. This is more complicated then you think however. Some cards will require being "flashed" as though they're Mac GPUs, while others can do most (but not all) things without it (and can be flashed for more compatibility.) Again, follow the guide in the article.

I hope this was helpful. Again, this machine–unless it's a fun project–probably isn't worth your time or money. But hey, if you want, go ahead.