Apple PC Compatibility Card - Manual (Page 125)

Connecting two monitors
If you connect two monitors, you see the Mac OS environment on one and
the PC environment on the other. The monitor connected to the PC
Compatibility Card shows the PC environment. You can also switch between
Mac OS and PC environments on this monitor if you have a video card.
You can use any combination of Mac OS–compatible and PC-compatible
monitors (with the proper cable adapters, available from your monitor vendor
or Apple-authorized dealer).
Multiple-scan monitor: If you want to use a multiple-scan monitor from a
manufacturer other than Apple to display the PC environment, you also need
to use a VGA-to-Macintosh adapter (available from your computer vendor).
You connect this adapter between the monitor’s cable and the loopback cable.
IMPORTANT Before you begin, shut down your computer, turn off your
monitor, and unplug all equipment. Then follow the steps in the section for
your Macintosh computer.
WARNING Do not plug a monitor into the joystick port (marked with the
icon ), and do not plug a joystick into a monitor port (marked with the
icon ™). Serious damage can result to your equipment.
125 Connecting Monitors and Other Equipment