NT had it first, but NT didn't really get much of any consumer exposure. Windows 95 was much closer to the Windows 3.1 everything-shared memory model: 16-bit apps (which were still in widespread use) continued being able to access hardware and each others' memory, and memory belonging to the most recently executed 32-bit app. NTVDM in Windows 2000 also supported 16-bit apps, but they were strictly isolated from each other, the hardware, and any 32-bit app.

The upshot was a 16-bit utility that would crash or corrupt an unrelated app (or the entire machine) in 3.1 or 95 would only crash itself in 2000. The driver model was also completely redesigned, but I don't know much about that.

Any time you hear the old meme about Linux being more stable than Windows, it's important to realize it dates back 20 years when Linux had per-process virtual memory and Windows did not.