They are, you can disable them in the registry.

> They posed no real risk to my single-user gaming machine and the fixes had an unacceptable performance burden IMHO.

Where are you seeing a performance burden? The spectre/meltdown patches had no impact to game performance: https://www.tomshardware.com/reviews/gaming-performance-melt...

Are you sure they are not optional? I remember disabling various security updates at the time, but unfortunately I wasn't testing whether performance in games was affected positively after removing them. I can only say that it felt as it had been faster, but I hadn't measured FPS.

My understanding is that newer Windows version contain microcode updates for the processors, and once they are applied, they are in there for good.

Microcode doesn't flash the CPU, it's loaded at boot time, you can remove it and disable the software mitigation.

Same on my Chromebook Pixel LS too. They were optional but now they added all kinds of additional mitigations and are also adding linux throttling and in the last 6 months or so I probably have gained ~60% compile time.

There's a performance mode that Google has a support article for. Google exactly "Change your Chromebook’s performance setting", and you should see it.

If lscpu still shows some offline cpus (let's say cpu 1 and 3 are offline), echo 1 >> /sys/devices/system/cpu/cpu<1 or 3>/online. Run lscpu again, and you should see all CPUs online and 2 threads per core.

Do you not browse the web on that machine?

You can toggle/check mitigations with a program called InSpectre.