You've probably known about computers your whole life. But computers have not really been around for very long. Computers started to become popular with big companies in the 1960s. Computers didn't become widespread in homes and schools until the 1980s.
这里的around是adj没错,但也有具体的含义。根据字典的解释:
[quote=AHD]
ADJECTIVE:
1. Being in existence: Our old dog is no longer around.
2. Being in evidence; present: asked if the store manager was around.
[/quote]