To me that was Windows 2000. One day in 1999, I was at the local bookstore going over computer magazines and one of them came with CD to preview Windows 2000. I was mostly a Windows 98/RedHat user at that point, so I decided to try it out.
It almost instantly won me over with the leap in stability due to the NT kernel, but the craziest thing was this feature called "Hibernate". This was the time when booting was painfully slow, and here was a feature that not just booted rapidly, but dropped me into the previous session with all apps open! It was pure magic. I switched over to Linux exclusively a few years after that, but this was the feature that prolonged that decision for a long time. I don't think Linux ever got a useable hibernate, but the feature became not as necessary due to the advent of SSDs.
It almost instantly won me over with the leap in stability due to the NT kernel, but the craziest thing was this feature called "Hibernate". This was the time when booting was painfully slow, and here was a feature that not just booted rapidly, but dropped me into the previous session with all apps open! It was pure magic. I switched over to Linux exclusively a few years after that, but this was the feature that prolonged that decision for a long time. I don't think Linux ever got a useable hibernate, but the feature became not as necessary due to the advent of SSDs.