The onboard display ports are capable of the below. This is from Intel's site and the H55 specs.
PCH Display Interfaces
The PCH has four display ports, one analog and three digital ports B, C, and D. Each
port can transmit data according to one or more protocols. The digital port B can be
configured to drive natively HDMI, DVI and DisplayPort or can be connected to an
external device (SDVO) that converts one protocol to another. Examples of these are
TV encoders, external DACs, LVDS transmitters, HDMI transmitters and TMDS
transmitters. Digital ports C and D can be configured to drive natively HDMI, DVI and
DisplayPort configurations. Each display port has control signals that may be used to
control, configure and/or determine the capabilities of an external device.
The PCH has one dedicated analog port.
The PCH’s analog port uses an integrated 350 MHz RAMDAC that can directly drive a
standard progressive scan analog monitor up to a resolution of 2048x1536 pixels with
32-bit color at 75 Hz.
The PCH SDVO port (configured through Digital Port B) is capable of driving a 200 MP
Each Digital port is capable of driving a digital display up to 2560x1600 @ 60 Hz using
DP and 1920x 1200 @ 60 Hz using HDMI, DVI (with reduced blanking).