For a brief period, the kernel tried to deal with gamma rays corrupting the processor cache
At one point, the following code was added to the part of the kernel that brings the system out of a low-power state:
; ; Invalidate the processor cache so that any stray gamma ; rays (I'm serious) that may have flipped cache bits ; while in S1 will be ignored. ; ; Honestly. The processor manufacturer asked for this. ; I'm serious. ; invd
I’m not sure what the thinking here is. I mean, if the cache might have been zapped by a stray gamma ray, then couldn’t RAM have been zapped by a stray gamma ray, too? Or is processor cache more susceptible to gamma rays than RAM? The person who wrote the comment seems to share my incredulity.
Less than three weeks later, the INVD instruction was commented out. But the comment block remains.
In case we decide to resume trying to deal with gamma rays corrupting the the processor cache, I guess.
Bonus chatter: One of my colleagues wasn’t part of this specific change, but recalled that these sorts of strange-sounding requests were not uncommon, especially for early processor steppings. The workaround was removed once the problem was fixed in microcode or in a later processor stepping.
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There is a market for “Rad-Hard” components. They tend to be super expensive parts. I find it hard to imagine a space vehicle using an embedded computer that is running Windows.
I have no trouble whatever imagining that. But the key here is “early processor stepping”. Cosmic rays had nothing to do with it.
In my world – space vehicle == satellite (like GEOS-R, or communications). Those use customized hardware running customized OS’s. I guess could imagine some UI type computer on the ISS, but that is a special case.
c. 2008: “Invalidate the gamma rays (I’m serious) that may have flipped cache bits while in S1 will be ignored. Honestly. [processor manufacturer] asked for this. I’m serious”
>> Or is processor cache more susceptible to gamma rays than RAM?
Certainly a possibility, as there are vendors of rad hard/tolerant SRAMs, and standard ECC likely mitigates some issues. Some applications all have to deal with unusual environmental concerns, and have corresponding rules & regulations requiring protection against things like, for example, bits flipped due to gamma rays. Medical devices & particle accelerator could certainly be running Windows.
If you were building Bruce Banner’s Hulkimatic 2000, you can either spend $$$ on a processor with ECC cache, or simply clear the cache after each firing of the particle accelerator. Fair warning: cost overruns make Hulk angry.
You guys know that there is a thing called NDT (Non-Destructive Testing) they do digital radiography and they use Windows computer to run the software required to extract the information from the sensors. This involves using nuclear sources to take the shots, Wich can entail some radiation affecting the computer that is being used.
The companies that use these computers do not spend the $$$ to buy the parts that are nuclear shielded.
