I'm currently using an old iMac that can't upgrade the OS past 10.11.6. I was gifted an old Mac Pro 4.1 with 2.66 GHz Quad core Intel Xenon processor. I tried updating its OS and it actually didn't even upgrade to 10.11.6.
Can I upgrade the processor or make other upgrades that will allow me to install the most current version of the OS?
If so, what would I need?
Mac Pro
The path most traveled by users who want to get more life from these Mac Pro 4,1 models is to force-upgrade to the firmware from the 5,1 model. That will essentially turn it into a 5,1 model for most software update purposes.
That is not something we can tell you how to do here, because novice users might damage their computers or their person.
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This site is a great resource for all things about the 2006-2012 silver tower Mac Pro:
https://blog.greggant.com/posts/2018/05/07/definitive-mac-pro-upgrade-guide.html
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Upgrade Mac Pro 4.1
