[OT] Virtualization (WAS: UNIX V7)

2009/6/12 Cameron Kaiser <spectre at floodgap.com>: A fair point, but then, that's the key part of the revelation that the people behind VMware had for how to virtualise a non-Popek&Goldberg-compliant instruction set architecture (ISA). The way VMware works is by running user-mode code directly on the native chip, but ring 0 (supervisor- or kernel-mode) code through a caching software emulator. So CPU emulators were a key enabling technology for x86 virtualisation to happen. First full emulation, then partial emulation for increased performance, then once such products had popularised the technology, virtualisation instructions were added to the x86 ISA. But other examples exist of non-native OSs running totally or partially inside VMs: - MC68K code on classic MacOS running on a PowerPC, where the OS hosts an emulator at a very low level, through which most of the actual OS code itself and many applications run; - the MC68K emulator on PalmOS 5 on ARM; - AlphaMicro's MC68K emulator on Intel x86 machines for running AMOS; - Charon-VAX running VMS on a VAX emulator under VMS on an Alpha. All these could be considered as straddling the line between a pure one-platform-on-another sandbox-type emulator and an OS that can run non-native code side-by-side with native code, no? I think the dividing line between the 2 is pretty blurry... -- Liam Proven ? Profile: http://www.linkedin.com/in/liamproven Email: lproven at cix.co.uk ? GMail/GoogleTalk/Orkut: lproven at gmail.com Tel: +44 20-8685-0498 ? Cell: +44 7939-087884 ? Fax: + 44 870-9151419 AOL/AIM/iChat/Yahoo/Skype: liamproven ? LiveJournal/Twitter: lproven MSN: lproven at hotmail.com ? ICQ: 73187508