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I grew up (career wise) on CTOS systems with 286/386 processors that could address the full 16MB in protected mode without memory extenders or expanders that were available for DOS back in the day. Also premptive multi tasking. It was a great OS to learn on. more info - https://web.archive.org/web/20080828190425/http://www.byte.c...

> what we have now

x86 processors still boot into real mode…

It's my understanding that UEFI actually comes up directly into long mode?

"UEFI firmware performs those same steps, but also prepares a protected mode environment with flat segmentation and for x86-64 CPUs, a long mode environment with identity-mapped paging. The A20 gate is enabled as well."

- https://wiki.osdev.org/UEFI

This inadvertently triggered my A20 gate rage.

Unfortunately most BIOS services are only available in real mode, so it's often necessary to switch back and forth.

What's real mode?

https://en.wikipedia.org/wiki/Real_mode