Editor's Note: AMD has reached out and clarified that Windows 10 Pro is officially recommended for use with the Ryzen Threadripper 3990X. It said that "We understand that this suggestion has been made by some reviews, and our team is presently diagnosing, but that is the official recommendation".

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AMD’s Threadripper 3990X is undoubtedly a mighty high-end desktop processor bristling with 64-cores and 128-threads, but Windows 10 Pro can’t actually deal with the latter – it’s just too many threads to handle, apparently.

As you may be aware, Windows 10 Home can’t handle any more than 64-cores (or threads), but Windows 10 Pro can supposedly cope with 128-threads, at least according to the official specs of the OS.

However, as discussed in Anandtech’s review, what actually happens when you run a Threadripper 3990X in a Windows 10 Pro PC is that the operating system splits those 128-threads into two separate processor groups of 64-threads. And the OS even refers to these as two separate ‘sockets’, as if it was a dual-CPU machine.

Sadly this isn’t a simple labeling issue: splitting the 3990X into two CPU groups actually impacts on real-world performance.

It can be the case that an application might be launched inside one group, and even though it’s a multithreaded app, it may only be able to access those 64-threads in its group, rather than the full 128-threads – effectively detracting from its performance.

The end result is that Anandtech observed “a lot of slowdowns in some benchmarks”, although disabling SMT (simultaneous multithreading) cured the problem, but of course then you are only running with 64-cores, even if you still get “most of the performance” of the 3990X, the reviewer notes.

Thread dread

How big a problem is this? To be fair, Microsoft no doubt didn’t expect systems running Windows 10 Home or Pro to be pushing above 64-threads, which is understandable to an extent.

Furthermore, those who can afford the eye-watering asking price of the Threadripper 3990X – namely $3,990 (£3,699, AU$6,499) – likely won’t be too concerned at springing a hundred extra notes (or so) to also upgrade from Windows 10 Pro to Windows 10 Pro for Workstations.

The latter is the version of Windows designed for really powerful high-end PCs, and it is capable of recognizing all the threads that the 3990X has to offer (Windows 10 Enterprise is also fine in this respect, as you’d expect). Linux users won’t be hit by any thread-related gremlins, either.

As a final note: according to some of the comments we’ve seen on Ars Technica (which highlighted Anandtech’s review), Windows 10 Pro has just received an update which allows it to see the 3990X correctly with all its glorious 128-threads.

So this issue could be in the process of disappearing, anyway, but obviously take that with an appropriate dollop of caution.

In other Threadripper 3990X news, the chip has been overclocked to 5.5GHz and is setting world records left, right and center.