This is a different and refreshing perspective. I've never looked from the perspective of W/mm². OTOH, the number I've given is calculated by eyeballing the per core internal thermistors, provided by lm_sensors (hence by CPU itself).

So, per die sensors are probably reading somewhat lower numbers, but the core's cooking at 70 degrees C internally. Nevertheless, bigger die surface inevitably allows better heat conduction and reduces internal stresses considerably, when compared to a desktop part.

Desktop use is also very uneven, leading to a lot of large changes in temperature (35 -> 80 and back), which causes more material stress, than when everything is loaded evenly all the time. The same is true for electrical transients.

If you have a good cooler with lots of thermal capacity and good fan (like an Arctic Cooling or Noctua, nothing at the extreme end), the increase is very gradual. Also, short spikes in loads are well absorbed with minimal temperature changes.

Nevertheless the numbers you mention are neither unrealistic, nor impossible in stock cooling and/or sustained load scenarios.

5950X with the top of the line noctua cooler jumps from 35C to 80C very quickly when a single core is loaded at 100% (this is the worst case, because it leads to max voltage being applied to the CPU cores (because of boost to almost 5GHz), compared to loading all 16 cores at 100%, which will result in just 60˚C temperature sustained over long periods of full load). So interestingly, compiling the Linux kernel with 32 threads is less thermally straining on the CPU than browsing the web and a single page loading 10 different animated ads.

This mirrors my experience with Zen 2 and 3 as well. Multi-core loads result in just a few W per core and decent temperatures, while few or single core loads push per-core power into the 12-16 W region and the temperature rise/fall is basically instant (brick-wall at 10 Hz update rate, though it's unclear what filtering is applied and how the CPU derives a single temperature from its probably numerous sensors), which suggests that they're not limited by the cooler, but rather by the thermal impedance from the active area to the cooler. The core itself is really tiny (iirc around 4 mm²)...

This is my conundrum when pondering buying a Threadripper 3970x / 3975x Pro workstation: aren't those chips cooked very aggressively when loaded, even with very good coolers? Doesn't that mean that one day the CPU might just burn?

I really want to buy a proper serious workstation and I can afford it in a few months but I keep wondering: is now the best time for it?

I wouldn't really worry about it. I have an overclocked 3970x and a Noctua air cooler keeps it much cooler than the Intel 6950X I had before (also aircooled, with an even larger Noctua cooler). Air cooling is more of a limit to how high an overclock you can get; normal operation will be no problem for any cooling system designed for Threadripper.

There's never a good time to buy a new computer. It's always going to be obsolete before you open the box. Though in this case, one might wait for the Zen 3 Threadrippers.

Thanks for the feedback, it's reassuring. As other posters said, I am worried because it's a workstation which means it won't have consistent load, and material stress is much more destructive in the thermal conditions of expanding and contracting. So if in your ~8h workday your station gets stressed for 2 or so hours in irregular intervals, how destructive is that, objectively?

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As for the Zen 3 TRs, well, to be fair, I am not looking to blow $50k on a workstation. :) I am more interested how -- and if -- they will drive down the prices of the TR 3900 SKUs...

It probably won't drive down prices that much. You won't want the old thing, and the incremental cost between generations is not the expensive part of a workstation. I have bought old parts before (to replace broken parts), and my experience is that the price didn't change much. What was a $130 motherboard when brand new, is $130 when a generation old. Does it make any sense? Nope. But that seems to be how it is.

You won't spend $50,000 on a workstation just by using current-generation parts. I think when you see a workstation that costs that much, it's because it has multiple GPUs in them. Pro GPUs are always artificially overpriced, and given the GPU shortage, they're now even more overpriced.

I did a quick pcpartpicker expedition and found that using last-gen parts saves you about $1000 on a $6000 32 core Threadripper workstation. I compared last-gen SSDs, consumer GPUs, processor, and motherboard, and picked relatively high-end parts. You will save more money by dropping to 24 (or heaven forbid, 16) cores, not getting an extreme motherboard, getting 64G of RAM instead of 128, etc.

This could all be invalid in a few months. It is hard to separate "market is always crazy" from "this whole COVID thing is going on". Building a workstation during the pandemic was a pain -- I bought a used GPU, and didn't get ECC memory because nobody would sell me any. If you wait a year, that is likely to improve, and there will be newer hardware. But, if you need to do some computing between now and then, you don't have much choice but to buy what's available now, and it certainly makes for a very good computer.

Thanks for the check! Much appreciated, it did put my mind at ease.

I realized I was looking at several custom-made TR Pro workstations and they of course have a hefty markup on top -- custom cases, custom cooling, pre-added several PCIe NVMe riser cards, plus style price tag I suppose, etc. Should have looked in PC Part Picker indeed.

And yeah, last-gen tech very rarely gets discounted even by normal people who just post ads in local Craigslist-like websites (like OLX). Stuff that's 2 or more generations ago is discounted, but not last gen. Puzzling indeed, especially having in mind that this last gen tech is very soon going to be "two gens ago". Oh well.

As for ECC RAM, I hear you. I was unable to find such anywhere officially but lucked out that one guy in the local OLX was having loads of it but just didn't post the ads due to being very busy (we communicated because of other ads) and then I just bought 64GB ECC DDR3 RAM from him for a home NAS that I am gradually expanding.

I'm definitely very interested in having a TR Pro workstation; started getting sick of Macs and their artificial slowness. I got the iMac Pro and granted, I have it connected to my TV where it plays Twitch streams all day but hell, a lot of stuff on the terminal (that's not Python) just works slower than it does on a meager i3 Linux machine that I have lying around.

So I do want a TR Pro machine but I am very curious about TR 5000. A release is expected in August which isn't that far away. On the other hand, the TR Pro 5000 might take several more months on top. Hmmm. Decisions, decisions. :)

I wouldn't focus too much on the Pro SKU. It has a slower base frequency and boost frequency, with the upside that it has 8 memory channels and supports 2TB of RAM. If you need 2TB of RAM and 8 channels, it's what you need, but quad channel memory is still very good. Most desktop-class machines are still 2 channel.

There is something to be said for the prebuilt workstations from reputable vendors. It shows up in a box, and starts working. I have strongly considered that angle; being a system integrator is tough. If something doesn't work, it's a week cycle time where you find a new part, organize the RMA of the faulty part, etc. and there is a potentially unbounded amount of time spent tweaking. Meanwhile, HP or Lenovo just ships you a computer; they tested it and it works. You pay several thousand dollars for the privilege, but it might be worth it. (And if you want a TR Pro, you have no choice. AMD doesn't sell them to consumers.)