On your latter point (pointers) I've heard that argument before. I work with somebody that turned out not to know about hash tables. I could spin a tale about how this meant they were so wide eyed they'd just be incapable of doing anything valuable (an argument made so many times on here). Instead, I took 15 minutes and taught them about hash tables and how to do them in C++. A few pointed questions about run time and the constants implied by the promise of O(1) (i.e a good question), and from then on every time a hash should have been used sure enough, they used one. Even showed initiative and added a memcache type interface to some of our code that was performing very slowly due to poor access patterns.

I guess it is lucky for us that when they interviewed they didn't have an interview question that involved hash tables, because they would have been bounced for not hitting the ground running.

I bet I know a lot about a field that you don't. I wouldn't bet that you couldn't walk in and pretty quickly become useful, given that you've learned other things, and at one time I didn't know this field either yet somehow, somehow, learned it. I think you would do just fine; and I think somebody that can get a PhD in CS can handle the math that 2^16 < 2^64, even if they haven't thought about the implications re allocations.

Different perspective: I believe for most CS persons this would be a 5-minute-difference... i.e. it would take 5 mins for them to understand/research 64 bit OS pointers size. So basically you're penalizing potential good candidates for just 5 minutes of their life.

Yes, it may be only 5 min.

But it tells a lot about the amount of "just 5 min" things they don't know.

I was asked once what load average knows (and I didn't know it). Because my background wasn't in sysadmin.

The fact that you know one fact or doesn't is immaterial, but it's a good proxy.

Your hiring decision should not be based on only that, of course, but let's say it's a pixel in a picture.

Different perspective: I'd prefer to hire the astronomy PhD who knows the basics of the craft over one who doesn't. Reflecting vs refracting is pretty simple - astronomy doesn't really interest me and I'm aware of the differences. It's fundamental to the optics, and understanding the differences helps understanding why real data looks different depending on method of acquisition. Why not penalise the person that doesn't know the basics? You wouldn't forgive a carpenter for not knowing the difference between a hand saw and a table saw, yet they both cut wood and the difference takes all of a few seconds to learn.

For example: I'm a midrange DevOps/Sysadmin/Whatever-it-is-these-days. I will likely never be a senior. The (real) seniors are the folks who go home and mess with hardware and pull new toys apart to see what chips they were made with and so forth. I like to go home and play games. I do my job competently, but I don't have the underlying knowledge that those guys do. If I was up against one of those in a job application, then you'd be crazy to hire me at the same salary as a senior - there'd have to be a pretty big black mark against the senior, like being completely unpersonable or abusive or somesuch. Or the role used some of the other things I'm decent at. Perhaps a colloquial way to put it is that I live these things, but the seniors live and breathe them :)