For me, I'd say anything before Intel's Core I series CPUs, which puts it before 2009.
I Think I had first multi core (core duo) before 2009 and already in XP era.
I think XP era of computers connected last bit of retro PC computing somehow with modern windows of today. if not then Windows 2000 was for sure something like that to me. I still tried to launch MS-DOS apps in Windows 2000.
-h1
... Xerox Alto was the thing. Anything after we use is just a mere copy.
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