From hands-on experience, I've learned that v86 initially had some severe, ugly warts, which made writing a v86 "hypervisor" way more tedious, and make it run s

From hands-on experience, I've learned that v86 initially had some severe, ugly warts, which made writing a v86 "hypervisor" way more tedious, and make it run slower, than what seemed reasonable. These limitations were addressed in much later CPUs in the so called "VME" extensions, for which there was apparently quite some drama related to NDAs, and subsequent reverse engineering: https://www.rcollins.org/articles/vme1/ https://www.rcollins.org/articles/vme1/ My (long abandoned) toy OS used virtual 8086 to provide "DOS services" support. The idea was that I could focus on the interesting parts of the OS, and outsource everything that I either hadn't gotten to yet, or that I didn't want to get to, to DOS. That included several devices, the filesystem, an entire shell (command.com isn't great, but better than nothing), even networking through packet drivers if needed. The OS was a "modern" and full protected mode true multitasking OS, but one of its task was the DOS instance you started it from, transplanted as a v86 task, and my OS could just call into that (and vice versa, so you could run DOS programs that call into my OS). Initially, even allocating memory would just ask DOS to do the bookkeeping! (I never got to implement VME since I made v86 work on itself, and I dropped this toy project once my work fully shifted to working on real OSes at that level anyway.)