Y2k Bug

This was my first venture into portable computers; my father bought it for himself but could not get on with it so I had it. I was about 1989 something like that I remember showing it to a friend and we noticed you could not put a date into is pass 1999. I spoke to my technology teacher about it and he said it would be obsolete my then, it was but 10 year on i worked for nearly a year on getting other systems that would not work pass 1999.
I fired it up the other day, it still works but only in the past