A major upgrade of the Macintosh operating system introduced in 1999. System 9 added more native PowerPC routines in the Toolbox and provided tighter integration with Sherlock. See macOS.
"System 9." YourDictionary, n.d. Web. 16 August 2018. <http://www.yourdictionary.com/system-9>.
System 9. (n.d.). Retrieved August 16th, 2018, from http://www.yourdictionary.com/system-9