80386 Protection

I've wondered for a long time if we would have been able to make do without protected mode (or hardware protection in general) if user code was verified/compiled at load, e.g. the way the JVM or .NET do it...Could the shift on transistor budget have been used to offset any performance losses?

ah, PDE/PTE A/D writes... what a source of variety over the decades!

some chips set them step by step, as shown in the article

others only set them at them very end, together

and then there are chips which follow the read-modify-write op with another read, to check if the RMW succeeded... which promptly causes them to hang hard when the page tables live in read-only memory i.e. ROM... fun fun fun!

as for segmentation fun... think about CS always being writeable in real mode... even though the access rights only have a R but no W bit for it...

Interesting to see how hardware designers of yesteryear did things, and why CPUs are so complicated and have so many bugs.

Article states that win 3.0 used 32-bit flat addressing mode, but when win 95 launched ms said win 3.0 didn’t (in 386 mode).

Made me think of the old Desqview

> These features made possible Windows 3.0, OS/2, and early Linux.

And also--before Linux--SCO Xenix and then SCO Unix. It was finally possible to run a real Unix on a desktop or home PC. A real game changer. I paid big $$$ (for me at the time) to get SCO Xenix for my 386 so I could have my own Unix system.