Simplify the following text for a Grade 9 native English-speaking person.
Original: Berkeley Software Distribution ( BSD , sometimes called Berkeley Unix ) is a UNIX operating system derivative developed and distributed by the Computer Systems Research Group ( CSRG ) of the University of California , Berkeley , from 1977 to 1995 .
Simplified: Berkeley Software Distribution ( BSD ) is a kind of the UNIX operating system that is distributed for free since 1989 . It was started by people in Berkeley , California , USA in the year 1977 .