Bill Joy, a Sun Microsystems Inc. co-founder who most recently served as the computer hardware and software maker"s chief scientist, is leaving the company. Joy joined Sun in 1982. "For 21 years, I"ve enjoyed the opportunities for innovation provided to me at Sun, but I have decided the time is now right for me to move on to different challenges," Joy said in a statement released Tuesday. Joy"s duties will be handled by Greg Papadopoulos, Sun"s chief technology officer.