I asked this question:

Popek and Goldberg defined when a CPU architecture is suitable for efficient virtualisation.

I know what to look for to find out if their theorem applies and how. But is there a list of CPU architectures somewhere that lists which architectures are compliant and which are not (and what instructions violate the definition)?

The Wikipedia article itself lists a few architectures but I am looking for something more complete.

And I was told that it is off-topic because "Questions seeking product, service, or learning material recommendations are off-topic because they become outdated quickly and attract opinion-based answers."

However, I don't see why a question about CPU architectures meeting certain technical requirements fits those criteria. I have also found several other questions that likewise ask for lists of CPUs and CPU architectures which for some reason did not seem to be off-topic.

Did the criteria change lately?

  • 3
    " is there a list of CPU architectures " says it all, I think.
    – Journeyman Geek Mod
    Dec 18, 2014 at 15:17
  • 1
    So do I. There are several questions for lists of CPUs, so asking for lists appeears to be on-topic. Why would a list of CPU architectures be off-topic? Dec 18, 2014 at 15:19
  • 1
    This question superuser.com/questions/533457/… asks for a list of graphics cards. It is on-topic. It's criteria are more subjective than the one in my question and I am sure perfomant graphics cards are outdated more quickly than CPU architectures. Dec 18, 2014 at 15:22
  • 1
    On the contrary, its not put on hold yet. I'll take a look at it in the morning for the relevant action.
    – Journeyman Geek Mod
    Dec 18, 2014 at 15:24
  • Says on my screen that it is on hold. I'll delete it in a few hours. Dec 18, 2014 at 15:25
  • I mean the video card question. Its on hold now.
    – Journeyman Geek Mod
    Dec 18, 2014 at 15:26
  • You are seriously considering putting a question on hold that is over a year old, has several upvotes and several answers, one of which is accepted? Are you going to hunt down all questions like that now? There are dozens of them that I could see. This will kill many of the most interesting questions that have always been regarded as on-topic. Dec 18, 2014 at 15:27
  • Here's another one for your hunt: superuser.com/questions/710870/which-cpus-support-1gb-pages Dec 18, 2014 at 15:29
  • 3
    Nope. And its entirely your fault for bringing it to my attention. Generally we leave these alone until someone complains, or there's an organised clean up. Generally this is a low priority task unless someone complains about it. The second one was a trivial fix to bring on topic.
    – Journeyman Geek Mod
    Dec 18, 2014 at 15:30
  • I still don't see how any questions asking for lists of things violate any of the off-topic rules. The rules certainly don't state anything like that. I deleted my question and will try to find a different forum to ask it in. Happy hunting. Dec 18, 2014 at 15:32
  • It's on topic, but it's out of scope. There are some things Super User is not suited for. We focus on those that we are.
    – random Mod
    Dec 18, 2014 at 15:44
  • Random, that is something I can accept. Thank you. Dec 18, 2014 at 15:46
  • We don't hunt for old questions that are no on topic, but those questions, at the end of the day are not on topic.
    – Ramhound
    Dec 19, 2014 at 2:48

2 Answers 2


You question, while on-topic, is not definitively answerable.

TL;DR: To put it plainly your question does not fit in the simple question and answer paradigm.

... is there a list of CPU architectures somewhere that lists which architectures are compliant and which are not (and what instructions violate the definition)?

You were essentially asking for someone to provide a list (or even a list of lists) of resources. That is, in no uncertain terms, a learning material recommendation.

Even if such a list exists and is currently up to date it would be out of date next week.

If the question were to be make "Post a list here, on this site, that meets these criteria" then it would be too broad. There could be a thousand answers.

But, and this was the crux of the matter for me, you could never choose the undeniably (verifiable by the larger community) correct answer. One person could post a list that gives a more complete (copy-paste) list of architectures but another person posts an abridged list that only lists a few architectures and a small subset of instructions that violate your definition. Which of those two answers would you mark as correct?

The same goes for "give me a link to a website that does X". One may be a better list, another might have a thorough examination of a smaller list, another site may be a balance of the two. Which site would be the correct answer in your case? Maybe it's none of them, maybe all three. How would you award the "correct" answer? I would have to say that you simply cannot.

To quote What types of questions should I avoid asking?:

You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page.

Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you’re asking too much.

Your question might be answerable, but there is no way to determine if one answer is more "correct" than any other answer.

  • The P&G theorem makes it rather specific whether a CPU architecture qualifies or not. And it's impossible for the list to change in the short or mid term. Dec 18, 2014 at 18:01
  • The fact the list can change makes the question hard to answer.
    – Ramhound
    Dec 19, 2014 at 2:50

To put it bluntly, nearly nothing makes a mod's life more difficult than 'Why was my question closed, and this similar question was not'. Closures are an ongoing process, and telling us another question should have been closed, then complaining when it was... Well yeah.

I'm also a little unclear how

Questions seeking product, service, or learning material recommendations are off-topic because they become outdated quickly and attract opinion-based answers. Instead, describe your situation and the specific problem you're trying to solve. Share your research. Here are a few suggestions on how to properly ask this type of question.

Does not apply to a question that explicitly asks "But is there a list of CPU architectures somewhere" - You're asking essentially, explicitly for an off site resource. In this case I'd deem this as a learning material request off the snippet you gave us. For a fuller treatment, you may consider actually linking the question so a mod or 10Ker can take a look and give you a critique.

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