I love these newbie questions; in part because I used to have similar ideas. When they differ from my newbie questions, I learn more about the mindset of a layperson interested in technology and I hope it makes me a better communicator.
Is it possible to have virtual instances of a 6502 system? Yes. The
hardware is relatively simple. The software is as difficult as you want it to be and it may be the most difficult software which you ever write.
Not a 6502 example, but I've seen a multiplexed clone of a Sinclair ZX Spectrum. The original models were shipped with 16KB DRAM or 48KB DRAM. A friend of a friend wanted to clone the 48KB DRAM model for reasons which were never explained to me. However, at the time of construction, the smallest DRAM chips were one megabit and the recently introduced four megabit chips were obscenely expensive. Unless you are in the habit of
making particularly perverse multiplexing circuits, eight separate one megabit chips are most conveniently arranged into 1MB DRAM. But who would want to implement a Sinclair ZX Spectrum and only use 3/64 of the DRAM? Therefore, it differed from the original by providing 16 virtual instances of a Sinclair ZX Spectrum where only one was running at any time.
I have no idea how this was implemented. Presumably, instance switching occurred at a common point of the screen refresh cycle. However, that doesn't explain how each instance would be initialized using an illegal copy of the unmodified Spectrum ROM.
The most obvious limitation of this implementation was the absolute lack of communication channels between the virtual instances. It would be brilliant if it were possible to increment and decrement through virtual instances and use it like a big undo when programming. But, no. It had no such functionality. It was also possible to do stupid things that were guaranteed to fail, such as switch instance while loading from tape. Also, don't expect peripherals, like printer or disk to work when you switch. Likewise, there are no background tasks.
When people say it is difficult, this is the type of difficulty they anticipate.
Is it possible to have virtual instances of a 6502 system? Yes.
It is possible to have virtual instances which communicate among themselves so they can run tasks in the background, not foobar the filing system, share a printer, network connection, audio and video? Yes but it is hideously difficult.
Writing an application is difficult. Writing a system resource, such as a database, is more difficult. Writing a device driver or filing system is another level of difficulty. Writing an operating system to co-ordinate resources is the most difficult of all. Part of the difficulty is the lack of diagnostics and debug. When an application fails, it typically fails on a relatively stable system. But how do you debug an operating system before you integrate the filing system? Likewise, it is difficult to simultaneously debug hardware and software. Is it one? Is it the other? It is both? It is me?
Anyhow, keep learning about hardware and software but I strongly recommend working down the software stack (from application to operating system) as you become proficient at each tier.
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