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Comment by chrononaut | Hacker News Reader

> old OSes rely on specific behavior of old systems and peripherals that can't be easily virtualized through KVM + QEMU or the like

This sounds interesting. Do you have examples of these behaviors where something is faulty using standard virtualization versus hardware-level emulation? (I know clock speed can make a difference.)

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AMD has relaxed a bit coherency behavior after page table manipulation leading to Windows 9x crashes:

https://blog.stuffedcow.net/2015/08/win9x-tlb-invalidation-b...

These crashes are not related to clock speed. While Windows 9x already cannot run on these CPU due to clock speed, the clock speed issues have mostly been patched in 9x.

Windows 9x couldn't even run on ~2007 era Intel Macbooks because of the A20 gate.

The Intel Macs were a strange not-quite-PC-compatible; the BIOS was EFI, and I believe things like the 8042 (which controls A20) weren't present although I'd have to check the schematic to be sure. That said, I'd be surprised if port 92h "fast A20" wasn't present --- that's been in nearly every chipset since ~386 or so.

Yes it can: https://www.youtube.com/watch?v=9si1le2EOGU (2009 iMac, they just use some himem.sys replacement).

And 9x can still be virtualized even on the latest Intel iMac, with nested paging enabled (or not). On AMD, you need to disable nested paging due to the above change in behavior.

This article goes into some specifics for OS/2: http://www.os2museum.com/wp/why-os2-is-hard-to-virtualize/

win 98 had a bug which would cause win98 to not boot on faster AMD systems.

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