HP b2600 Administration Manual page 78

In overlay mode, the X server runs only in the overlay planes. Since only 3 or 4 planes are available in
the overlay planes on VRX devices, the number of colors is very limited. To operate in overlay mode,
the overlay device file should be specified as the primary screen device. For example:
/dev/ocrt
or
/dev/o4crt
In combined mode, the X server runs in both image and overlay planes. To configure the X server to
operate in combined mode, a primary and a secondary device must be specified. The
VRXSecondaryDevice is used for this purpose. For example:
/dev/ocrt /dev/crt
or
/dev/crt /dev/ocrt
Page 78
# Overlay mode using 3 overlay planes
# Overlay mode using 4 overlay planes
# default visual lives in overlay planes
# default visual lives in image planes
Graphics Administration Guide for HP-UX 10.20