One of the things that blew my mind in my early career was seeing my mentor open the side of a VMS machine (I can’t remember the hardware model sorry) and slide out a giant board of RAM, and then slide in another board the same physical size but it had a CPU on it, and then enable the CPU
The daughter board in that machine could have RAM or CPUs in the same slot and it was changeable without reboots!
I have seen it. Yes, they technically exist. Nobody buys them though.
They are ridiculously expensive. Their use-cases in modern compute is a rounding error towards zero. We just don't build computers like that anymore, for good reason. Memory and CPU rarely fail, and when they do fail, they fail the entire box and just replace it. In 99.99% of all cases it's cheaper and easier to do it that way.
There are vanishingly small use-cases where it makes sense to do hotplug CPU/Memory. They charge accordingly.
Like I said in my parent comment, virtually nobody needs uptimes measured in literal decades. If you are in the .01%(rounded up) of compute that actually needs that, the chances of needing to do it with x86 is even smaller.
One example are the VISA and Mastercard payment processing platforms. The way they are designed requires 24/7 literal decades of uptime. When they have partial outages, they make international headlines and end up writing letters like this: https://www.parliament.uk/globalassets/documents/commons-com...
Exactly! One would never, ever do that with x86.