5,1 Mac Pro CPU tray

Grant isn't exactly clear, and I can explain much easier: The 4.1 (2009) Mac Pros use delidded CPUs on the trays, and the Mac Pro 5.1s do not. This means you cannot swap tray from a 2009 Mac Pro into a 2010-2012 Mac Pro or vice verse. However, you can swap a 5.1 single CPU to a dual CPU tray, or a 4.1 to a single CPU tray to a dual CPU tray.

4.1 Mac Pros firmware can be flashed to use the same firmware as a Mac Pro 5.1. This doesn't change which CPU trays can be used but rather enables 4.1 Mac Pros to be able to use faster RAM/CPUs and additional firmware upgrades to enable things like APFS booting, NVMe booting, Mojave support, etc.... which is what the above is trying to explain, which is needless information for you.

Generally, the CPU trays are as expensive as an entirely used Mac Pro so many users just opt to buy a low-end dual CPU 5.1 and just migrate any relevant hardware to that box, and buy CPUs on the aftermarket.

This video has nothing to do with DJstylus’s question.

Yes, you can swap single-processor tray to dual processor-tray, just BE SURE to use real 5,1 tray in true 5,1 Mac Pro (2010, 2012). Do not use 4,1 (2009 Mac Pro) tray in 5,1 Mac Pro, or the other way 5,1tray in 4,1 Mac Pro (2009).

For the genuine 2010-2012 model MacBook Pro 5,1 ONLY:

There are two different processor shelves, one with one heatsink and one processor socket and four DIMM slots, one with two heatsinks and two processor sockets and eight DIMM slots.

Buyer beware -- NOT interchangeable with the 2009 models 4,1 trays, even if the firmware has been upgraded so that it "looks like" a 5,1 model.

As rudo.ba says, 2010 to 2010 are interchangeable, (It is likely the two different processor shelves from a 2009 4,1 would interchange with each other, just not across models.)

OWC still offers certain processor shelf swaps and numerous chip upgrades as a service. They don't need a one-socket 2009 processor shelf, and there is not much of a market for 2009 single-socket shelf except to people whose one-socket shelf failed, so they do not offer the one socket to two socket upgrade for the 2009 model.

https://eshop.macsales.com/shop/turnkey/MacPro/2009_2010_Xeon_Processor/Apple_Mac_Pro_2010_1

You may not want to pay their prices, but their site will give you an idea about what is possible AND trouble-free as an upgrade path. On the other hand, their service includes a modest warranty for that price.

don't think so, watch the video.

https://www.youtube.com/watch?v=G4Ivlu8mCos

Why do you want to do this anyway? Are you running compressor?