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?

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rwmj a minute ago | parent | next [-]

I think the interesting thing about having protection in software is you can do things differently, and possibly better. Computers of yesteryear had protection at the individual object level (eg https://en.wikipedia.org/wiki/Burroughs_Large_Systems). This was too expensive to do in 1970s hardware and so performance sucked. Maybe it could be done in software better with more modern optimizing compilers and perhaps a few bits of hardware acceleration here and there? There's definitely an interesting research project to be done.

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st_goliath an hour ago | parent | prev [-]

Microsoft Research had an experimental OS project at one point that does just that with everything running in ring 0 in the same address space:

https://en.wikipedia.org/wiki/Singularity_(operating_system)

Managed code, the properties of their C# derived programming language, static analysis and verification were used rather than hardware exception handling.

	▲	avadodin an hour ago \| parent [-]
		Fil-C vs CHERI vs SeL4 vs YOLO I think hardware protection is usually easier to sell but it isn't when it is slower or more expensive than the alternative.