Several. But I'm lucky in that I worked for NetApp for 5 years which have several million NetApp filers in the field that were all calling home when they had issues, and Google which has a very large number of CPUs all around the planet doing their bidding. With visibility into a population like that you see faults that are once in a billion happen about once a month :-).
Two general kinds of failures though, the more common one is a system machine check (the internal logic detected the fault condition and put the CPU into the machine check state) which happens when 3 or more bits go sideways in the various RAM inside the mesh of execution units. Nominally ECC protected it can detect but not correct multi-bit errors. Power it off, power it on, and restart from a known condition and it's good as new.
The more rare occurrence is that something in the CPU fails which results in the CPU not coming out of RESET even, or immediately going into a machine check state. When you find those Intel often wants you to send it back to them so they can do failure analysis on it. The most common root cause analysis for those is some moderate electrostatic damage which took a while to finally finish the process of failing.
Some of the more interesting papers at the ISSCC are sometimes on lifetime expectancy of small geometry transistors. They are a lot more susceptible to damage and disruption due to cosmic rays and other environmental agents.
Microsoft released research that shows enthusiast overclocking has a clear increase in hardware faults.
[1] http://www.extremetech.com/gaming/131739-microsoft-analyzes-... [2] http://research.microsoft.com/pubs/144888/eurosys84-nighting...
[14865975.000023] Machine check events logged
MCE 0
CPU 0 BANK 2
ADDR 1438280
TIME 1384859595 Wed Nov 20 00:13:15 2013
STATUS d40040000000011a MCGSTATUS 0
MCGCAP 104 APICID 0 SOCKETID 0
CPUID Vendor AMD Family 6 Model 8
This will, of course, be getting replaced shortly, preferably before it does any real damage. Given it's a 2002-era chip, 11 years of service isn't exactly terrible.
I've seen quite a few UltraSPARC chips (especially IIIs) go over the years at work, and often had a shit of a time trying to get Sun to accept them as faulty and replace them.
Does this mean it didn't boot into Linux?
It would actually run for a day or two, serving up a modest PHP load, before crapping out.
Or how you notice how much more frequent your model of car is on the roads?
Another possible factor is that I find I pay more attention to things I've recently learned about more closely when I come across them, but ignore them when I either know them very well or don't know them at all. I don't know if this is true for anyone else.
The first would include the Kardasians for example. But just because they get mentioned a lot, you don't feel anything strange about hearing about them a lot.
Whereas the very essense of the phenomenon is that encoutering something multiple times seems strange to you.
In summary, some data centers are run hotter than recommended, which leads to a lot of mostly ignored domain resolution errors, which leads to a security risk.
And the failed part is either needed only on bootup or when the current gets going it doesn't stop until it's powered off again
Which wasn't a real problem for 'some' day-to-day use. This was in the mid to later 00's, so https wasn't quiet everywhere yet.
The problem manifested slowly. When ever I'd connect to HTTPS, my browser would crash. One sound card would phone home for an update, and my computer would crash. Randomly certain games would crash when ever anti-cheat software attempted to run.
It was just odd, and took a few days of hunting to find out what was actually going wrong.
That sounds like a huge cost to bear. Looking at e.g. a Haswell die photo [1], there are just four physical cores present for a four-core part. With that die area per core, you would take a ~15-20% area hit (that translates to 15-20% cost) just to have a spare core in case one failed some years later.
I have heard of manufacturers selling otherwise "defective" parts where a core or cache slice has a defect by relabeling as a part with fewer cores. But that's a manufacture-time decision, not a dynamic reconfiguration in the field.
[1] http://cdn2.wccftech.com/wp-content/uploads/2013/05/Intel-Ha...
It seems like the GP might be suggesting that a quad-core CPU will swap in another core when one dies. That doesn't happen. But the binning process allows them to still sell slightly defective silicon with disabled parts (cores, cache), which saves money.
On a related note, a lot of GPUs actually do have a few dozen execution units that are disabled by default and can be swapped in after stress testing at the factory. I believe some can even do that in the wild, but I could be wrong.
https://en.wikipedia.org/wiki/PlayStation_3#Technical_specif...
The cell processor had a main PowerPC core and eight floating-point SIMD co-processors called synergistic processing elements (SPE). For the PS3, one of the eight SPEs was disabled and another was reserved for the operating system, leaving the other six for developers.
Those were correctable errors, prime95 or memtest did not detect anything.
Failures were more prominent in memory...but they did happen. We also sent equipment through environmental testing that would force failures. I don't recall of hearing of any CPU failures. Although most of our equipment was DSP & FPGA based but there were some tiny 'lil CPU's there.
It's entirely possible that they overheated, but if they did it was due to poor cooling; we did not overvolt or overclock these machines.
The only times I've even heard about failing CPUs has been if they've been overclocked or insufficiently cooled(add in overvolting, and you get both :)) or physical damage during mounting/unmounting or otherwise handling hardware. And even then the failure has usually been elsewhere than the CPU itself.
Of course I am not saying it'd be unheard of, but for me frankly, right now it is.