I expect it'll be an ecosystem answer. Given that even personal devices might be expected to go to space or work in a dock or asteroid base, I'd expect most chips are defacto rad hard, probably by a combination of redundancy and lots of hardware accelerated software checks.

If the market demands space ready processors, and the military is primarily focused on space applications, I'd expect most of the best chips to support that radiation tolerant ecosystem.

Alternatively, we may develop better technology to block ionizing radiation in space. Then rad-hard will still be a niche application.

We may, but I never saw anything in Expanse to imply that.

If an environment is safe for humans, then it's safe for machines. Unfortunately this is a pretty high bar to clear and shows like the Expanse greatly undersell just how hard it will be to thrive on non-Earth locations in the solar system.

Machines can be a lot more fragile than humans though, mainly due to cost reasons. NAND flash memory chips now routinely code three or four symbols into each buried gate, which means that even a very slight disturbance can change its state. Without error correction (like most consumer hardware and software), it can cause real issues.

And there is ECC in every level of cache in every CPU and often on main memory. TMR is for radiation environments unsafe for humans.

Not sure if I understood your comment correctly, but there is certainly not ECC in every CPU and main memory. The majority of RAM sticks you can buy do not support ECC. The NXP i.MX 8 application processors and Raspberry Pis that I was using do not support ECC memory. Also, all Cortex-M MCUs older than Cortex-M7 have no ECC in the core, and even with Cortex-M7 it is an optional extension used by STM32H7 but not NXP i.MX RT1160, 1060, 1050, etc

Aren't humans already reasonable radiation hard? Cells are full of error correction. I would have thought with greater tolerance than an off the shelf chip.

I'm being rather vague with my defitions admittedly.

Yes, we are "reasonable radiation hard" optimised for the conditions on earth and the quite low radiation we get here.

But even so, cancer is a real threat, so increase radiation dosis and you will increase cancer rates. Along with long term dna damages and other perks.

Not at all. Try running your laptop on the ISS. You won't get far. Source: ran code on non-hardened commercial servers on ISS.

I don't know what you've done but that information is not correct. Standard iPads and ThinkPad laptops are used on ISS. The problem on ISS is not ionising radiation but that in zero gravity cooling by convection does not work anywhere near as well as on Earth. Without forced air circulation they just sit in a bubble of hot air.

I ran a bunch of code on standard servers lifted onto iss. Eventually we couldn't because the machines broke. I never said anything about radiation (but I was probably thinking that), just that this case refutes GPs claim that anywhere a human is safe, a computer is too.

I was wrong about ThinkPads, and I'm fine being wrong about that since ThinkPads are surprisingly robust.

No, just put them inside a radiation shield and pump heat out. Same protocol for the humans.

There was the scene in the final season where Holden had to extract information from one of the bad guy belters satelites, and he had to open the box that held a computer. I've been wondering what computer chips from 250 years from now would look like... surely they hit a wall as far as miniaturization goes at least a century back. Anyways, radiation hardening even near cutting edge silicon probably comes easy, maybe because the materials they make the chips out of are radiation hardened themselves?