Comment by lproven

I haven't seen a machine shipped with firmware RAID in decades.

It's still enabled in the firmware of some vendors' laptops -- ones deep in Microsoft's pockets, like Dell, who personally I would not touch unless the kit were free, but gullible IT managers buy the things.

My personal suspicion is that it's an anti-Linux measure. It's hard to convert such a machine to AHCI mode without reformatting unless you have more clue than the sort of person who buys Dell kit.

In real life it's easy: set Windows to start in Safe Mode, reboot, go into the firmware, change RAID mode to AHCI, reboot, exit Safe Mode.

Result, Windows detects a new disk controller and boots normally, and now, all you need to do is disable Bitlocker and you can dual-boot happily.

However that's more depth of knowledge than I've met in a Windows techie in a decade, too.