Suppose we define a machine architecture not for building hardware, but specifically for itself being easy to emulate? This is by analogy to para-virtualized device drivers, which are not there to model real devices, but to be easy to support in a virtual machine environment.

➢ Although simh is huge step in that direction ;) Yep, sometimes that's the easier solution. Remember the old Honeywell IMPs. BBN wanted to move forward, but all the code was in 516 emulators (having been ported over from the PDP-1, they should have realized that portability would be important). They built the C-30 to emulate the Honeywell. Of course, this isn't even accounting for the VAX emulating the PDP and the like. You do find some relics still running stuff. I remember seing a new computer being installed at some FAA facilities. It was some Apollo systems long after HP had pulled the plug on the DomainOS and the related hardware. I still remember a while when we were in the business of porting/selling MOTIF on a wide variety of platforms. One day, the reps from Stellar insisted they need their loaner machine back. This was a trade show unit and had an huge anvil shipping case. I packed it up and put it on our loading dock. The next day Stellar announced they were out of business. I didn't think anything about it for a couple of years when I went out to our loading dock and said "Is this stupid thing still here." They had never come for it. I then was called into our sales manager's office. Some guy needs a MOTIF for a Stellar. I chuckle. He goes "Yeah I know they're out of business." I tell him that today's his lucky day. I still have one. I uncrated the thing, wrote him out a tape, and packed it back up. Last I saw one of the CPU boards was hanging on the wall of our conference room as a decoration and another programmer and ripped out the Wyse PC the thing had in the top of it as a boot-up/maintenance processor to take home.