Sorry if this is duplicative, but I thought it clarified a point.
What I found in fixing overscan for a particular monitor: HDMI jacks on newer computers and video cards are supplied with default settings for configuration utilities, ATI Catalyst etc., for output to a TV (for resolutions used by TV's), which likes overscan in broadcast inputs, and also has monitor capability. Monitors with DVI inputs do not like overscan, and will letterbox or cut off some of the display when getting these improperly defaulted inputs from an HDMI output through an adapter to DVI. Some monitors with HDMI jacks (but no tuners) might process this output correctly, since HDMI is for TV. A video card with a DVI output has defaults for monitors which don't like overscan, so do not cause DVI monitors to letterbox overscanned inputs the way outputs from HDMI jacks do, just because the default settings for the output formatting differ between the two. Connecting newer HDMI outputs to DVI monitor inputs through pin-to-pin plug adapters presents a TV oriented format to a monitor preferring no overscan. So you need to adjust the overscan setting in the advanced, scaling options menu in Catalyst or Intel equivalent. Going the other way, putting DVI output to a TV through an adapter to HDMI, might need adjustment up or down. One effect observed besides letterboxing, is cutting off a small bit of the display from an incompatible overscan setting.
The overscan setting in Catalyst is a slider which is not active unless a resolution is first set which requires overscan. Then one can dynamically see the display shrink and expand as the slider is moved.