Complex sentence: It was operated by Quantum Computer Services of Vienna, Virginia, which in October 1991 changed its name to America Online, and continues to operate its AOL service for the IBM PC and Apple Macintosh today.
Split into simpler sentences: It was operated by Quantum Computer Services of Vienna, Virginia. In October 1991 they changed the name to America Online, which continues to operate the AOL service for the IBM PC and Apple Macintosh today.