This topic discusses the switches on older IBM-logoed EGA cards ONLY.
On non-IBM EGA cards, there may be more or fewer switches and they may
The DIP switches on the rear of the EGA indicate which display monitor
is connected to the card and which (if any) other adapters are in the
system at the same time. The switches are mirrored in memory. See
There is one CRITICAL thing to watch for: never plug a Monochrome monitor
into the EGA adapter unless the switches are set to accept it. A wrong
setting will actually do physical damage to the monitor!
In the following table, Primary indicates the adapter/monitor which is
first enabled when the computer is turned on. Secondary indicates an
optional second adapter/monitor which may be connected.
ON 4 3 2 1 Primary EGA connected to 40x25 color monitor
ON 4 3 2 1 Primary EGA connected to 80x25 color monitor
ON 4 3 2 1 Primary EGA connected to enhanced color monitor (CGA emulation)
ON 4 3 2 1 Primary EGA connected to enh. color monitor (best resolution)
ON 4 3 2 1 Primary EGA connected to Monochrome monitor
Secondary CGA connected to 40x25 color monitor
ON 4 3 2 1 Primary EGA connected to Monochrome monitor
Secondary CGA connected to 80x25 color monitor
Secondary EGA connected to 40x25 color monitor
Secondary EGA connected to 80x25 color monitor
Secondary EGA connected to enh. color monitor (CGA emulation)
Secondary EGA connected to enh. monitor (best resolution)
ON 4 3 2 1 Primary CGA connected to 40x25 color monitor
Secondary EGA connected to Monochrome monitor
ON 4 3 2 1 Primary CGA connected to 80x25 color monitor
Secondary EGA connected to Monochrome monitor
The three jumpers on the EGA control various features of the card. The
jumper/connectors are used as follows:
1 Supports enhanced color monitor
2 (640x350 and 64 color capability)
2 Supports color monitor only
3 (640x200 and 16 color capability)
P2 (not shown) is a connector for a light pen.
2 Sets EGA I/O ports to 2xxH
3 NOT supported by EGA BIOS