Matrox DualHead2Go: How It Used DVI to Span Displays

The Matrox DualHead2Go was an external multi-display adapter that allowed computers, especially laptops and systems with limited video outputs, to drive two independent monitors from a single display port. Released in the mid-2000s, it bypassed hardware limitations by tricking the computer’s graphics card into rendering an ultra-wide digital canvas, which the device then split into two distinct monitor feeds. By leveraging the bandwidth of Dual-Link DVI, the adapter delivered an affordable, plug-and-play multi-monitor workspace without requiring an internal graphics card upgrade.

What Was the Matrox DualHead2Go?

Developed by Matrox Graphics, the DualHead2Go belonged to a category of hardware known as Graphics eXpansion Modules (GXMs). During its prime, most consumer laptops and low-profile office desktops were equipped with only a single external video output. Standard operating systems and graphics drivers at the time could not easily output multiple independent display signals over that single connection.

The DualHead2Go acted as an external intermediary box positioned between the computer and the monitors. It required no internal installation, drew power via a standard USB connection, and relied on the host system’s existing GPU for all 3D acceleration and rendering. Users managed their screens using Matrox PowerDesk software, which provided features like bezel management and the ability to maximize application windows across a single monitor rather than stretching awkwardly over both.

How It Used DVI to Span Displays

The device's functionality relied on a technique known as EDID (Extended Display Identification Data) spoofing combined with the high transmission bandwidth of Dual-Link DVI.

  1. Spoofing an Ultra-Wide Display: When connected to a computer’s DVI port, the DualHead2Go did not identify itself as two separate monitors. Instead, its onboard controller presented a custom EDID profile to the host operating system. This forced the computer’s graphics card to detect a single, extraordinarily wide virtual monitor—for example, treating two 1920x1200 displays as a single 3840x1200 display.

  2. Utilizing Dual-Link DVI Bandwidth: Transmitting an uncompressed video signal of that size over a single digital cable required significant throughput. The "Digital Edition" of the DualHead2Go utilized a Dual-Link DVI input. While standard Single-Link DVI uses three Transition Minimized Differential Signaling (TMDS) data channels capable of handling resolutions up to 1920x1200 at 60Hz, Dual-Link DVI adds a second set of data channels. This effectively doubles the transmission bandwidth, allowing pixel clock rates fast enough to transport the massive composite frame across a single physical cable.

  3. Hardware-Level Signal Splitting: Once the GPU transmitted the double-wide frame down the Dual-Link DVI cable, the internal digital processing unit of the DualHead2Go intercepted the stream. The hardware sliced each incoming horizontal line of video directly down the middle, routing the left half of the image data to the primary DVI output and the right half to the secondary DVI output.

Because this splitting occurred entirely inside the DualHead2Go hardware in real time, there was virtually no latency, input lag, or additional processing overhead on the host computer's CPU. The individual monitors received standard Single-Link DVI signals operating at their native resolutions and refresh rates, completely unaware that their display data originated from a single shared video pipeline.