Yeah but software fails so often and repeatedly that it's rarely worth asking the question "is it software or hardware?"

Exploding batteries, bad wiring, design faults, silicon bugs and erratas, bad connectors, temperature problems... I've seen them all. It's more common than one may usually think, especially if you work in embedded. And somehow I wanted to tie the answer with the concept of the parent about space equipment.

BTW, "is it software or hardware?" is exactly what the boss asks first when a customer has a problem.

Regarding my reply to your parent comment, it sounds like we are both biased by our experience, we might need some data!

I agreed about the bias. When I read "software" I try to think about a broad spectrum of software applications, including the ones that are running in your fridge, router or the ISS.

When author (or most people, I believe) mentions software, it seems it's just apps (like food apps mentioned elsewhere) or web apps, that is just a fraction.

I wouldn't be so sure about that. My PC has an overclocked AMD processor with 32GB non-ECC RAM (because ECC ram wasn't even available when I bought it, let alone affordable).

Even if the software was 100% perfect, such a machine is expected to crash once or twice every year or so under full load just from the failure rate of the chips (cosmic radiation / quantum tunnelling effects). Especially RAM seems to have become fairly error-prone nowadays.

What software are you using that once or twice a year doesn't count as "rarely"?

My Viaplay app stops streaming and tells me I'm not connected to the internet several times a day (when I'm obviously still connected to the internet.)

Several times a week my phone's Netflix state doesn't match my TV's state, so I'm either not presented with the controls or when I press them they do nothing.

Cosmic bit-flips are rare enough to be newsworthy. https://www.johndcook.com/blog/2019/05/20/cosmic-rays-flippi...

If the faults were with the hardware, I'd expect the errors to be spread around the software that I use. But Firefox and Gmail always work for me (even if the JavaScript I'm served makes the machine unresponsive), whereas Netflix, Viaplay and HBO constantly misbehave.

Let's not turn this into a discussion of the meaning of "rare". We don't disagree, I believe. Sure, software bugs are more frequent. The point is merely that non-ECC RAM is fairly buggy by design and no amount of software will eradicate the crashes due to RAM faults. If you have 32GB or 64GB of RAM these should appear not too rarely, provided you actually use that RAM. Standard desktop CPUs also have surprisingly high error rate, but it's hard to find good figures. I've tried to find some, but apparently Intel & Co. hold them under wraps nowadays.

All uptime problems I have ever encountered were software related. It was just a matter of time before the software failed, but it would eventually fail in some way. The hardware was just doing what it was told to do.

"Correctness" in programming refers to mathematical correctness. As in formally proving your program to be 100% correct as apposed to proving your program correct for a couple cases using software blackbox testing.

This can be done and has been done but is not well known among the javascript boot campers that populate HN.