I have a mac 3,1 with dual Xeon's. It definitely has 2 CPUs because when I bought it I checked system information and is said 2 CPUs and I put better thermal paste on both of them just just to improve thermals which weren't bad but I figured it wouldn't hurt.

When I put everything back together it booted and I think I remember checking to make sure both cpu's where working correctly which, if I did ally check, they both where.

I recently downloaded cinabench and saw that is only recognized 1 cpu but I thought nothing of it and assumed it was just cinabench being weird.

Today I purchased a used hd 5570 and once I had installed the card and booted the computer I saw that in the system info it too only recognized one cpu. (I am fairly certain it had nothing to do with the card because in hindsight it seemed slower than when normal.

If you need any more information just ask, I'm happy to give it to you. I'd really appreciate some help, thanks.

  • Model Name: Mac Pro
  • Model Identifier: MacPro3,1
  • Processor Name: Quad-Core Intel Xeon
  • Processor Speed: 2.8 GHz
  • Number of Processors: 1
  • Total Number of Cores: 4
  • L2 Cache: 12 MB
  • Memory: 16 GB
  • Bus Speed: 1.6 GHz
  • macOS
  • Well if you have had it opened and put thermal paste on one of the CPUs, which one, the one that failed or the one that did not? Perhaps some info on why you felt the need to change the thermal grease. Did you remove the CPU itself at the same time? The more info the better. Please edit your question with the answers, don't answer in a comment. Commented Aug 30, 2020 at 0:17

1 Answer 1


This is almost certainly a hardware problem. As you're not sure that your second CPU was recognized after you unplugged and replugged it, it is likely that this is the event that caused the problem.

I would suggest shutting down the Mac, unplug power - and then remove the second CPU. Boot the system up and check that it works, and that System Information says 1 processor.

Then shut the Mac down again, unplug power - and carefully replug the second CPU. Boot up again and check System Information for the Processor Count.

If it still says 1 CPU, your problem is most likely either a defective CPU or a defective socket. The easiest way to check if to try with a different CPU. Perhaps you can get one cheap off eBay or perhaps you have access to one.

If it is a defective socket, then your options are very limited. With reasonable cost the only you can really do is to exchange the whole board.

  • After I saw this I switched the CPU's around and rebooted and it recognized both. I think last time I tightened the air coolers to much but what ever the issue was its now resolved. Thanks so much for the help I really appricate it. Commented Aug 30, 2020 at 20:58

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