The Macintosh II Portrait Display Monitor has three Apple Desktop Bus (ADB)
ports built into the monitor.
The Macintosh II Portrait Display Monitor has three ADB ports built into the
back panel of the monitor. This makes it easier for the user to configure the
Macintosh in a way that fits a user's workspace.
Why three ports when the Macintosh II has only two? Only two of the ports
are usable, because the third must be used to connect the monitor to an ADB
port on the Macintosh. Thus, one ADB cable runs from the Macintosh to the
monitor, activating the other two monitor ADB ports.