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If you flash the xserve3,1 bootrom to a cMP 5,1 then yes that CPU would probably work however that CPU doesn't support ECC RAM, and is limited to 24Gb of RAM, so it would be a poor choice of CPU unless you already have it. Also note that this CPU doesn't support being in a dual CPU system either.

You'd be better off with the W3690 (if single socket) or dual X5690 if dual socket, as they are basically the same CPU as the one you list but have ECC and a lot more RAM support.

Once on cMP 5,1 bootrom you can easily natively load mojave if you have the right GPU installed.
Or you can load other OS on xserve now via alternative methods.

Side note of caution, you will lose some DIMM slots and probably IPMI by doing this flash, neither of these have been verified to much depth.
 
Ok i will keep it original for now and I ended up buying it and I’m having trouble installing an os I’m trying Yosemite from a website. As of right now I have had no luck installing from a usb drive. I would love for some tips and tricks to get it booted from scratch.
Things to note:
- I am currently using a windows laptop and I don’t have a Mac
- this Xserve came with no drive bays (cheap price-60$)
- I am trying to use a sata pci card in the future but would like to use a usb hard drive as storage right now.
 
Since you don't have a Mac to create an USB drive to boot, perhaps this procedure would help? https://pureinfotech.com/create-macos-bootable-usb-windows/
I have tried this to no Avail. When I hold the option key a blank screen shows up with just my Mouse cursor. And if I don’t press the option key it acts like it’s reading the USB (light flickers) when the “missing files” pops up but nothing happens. I hope someone can help me with this and thanks.
 
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