Display Switch; Variable Capacitor - IBM AT 5170 Technical Reference

The following shows how the jumpers affect RAM.
Jumper Positions Function
1
and 2
Enable 2nd 256K of system board RAM
2 and 3
Disable 2nd 256K of system board RAM
~
RAM
Jumper
Note: The normal mode is the enable mode. The other
mode permits the additional RAM to reside on adapters
plugged into the
I/O
bus.
Display Switch
Set the slide switch on the system board to select the primary
display adapter. Its positions are assigned as follows:
On (toward the front of the system unit):
The primary display
is attached to the Color/Graphics Monitor Adapter or
Professional Graphics Controller.
Off (toward the rear of the system unit):
The primary display
is attached to the Monochrome Display and Printer Adapter.
The switch may be set to either position if the primary display is
attached to an Enhanced Graphics Adapter.
Note: The primary display is activated when the system is
powered on.
Variable Capacitor
The system board has a variable capacitor. Its purpose is to
adjust the 14.31818 MHz oscillator signal (OSC), used to obtain
the color-burst signal required for color televisions.
System Board 1-41