Simultaneous Video Output on Dual Displays Under Windows

(11 Feb 2008)

Video on Two Displays Not Always So Simple

Recently at work, I needed to set up a system for a presentation that would output video simultaneously to two displays, a touchscreen and a projector.  I encountered some interesting wrinkles along the way, an account of which might be instructive to whomever might happen to stumble into this page.  Similar issues might arise when giving a presentation from a laptop to a projector or other external monitor with the expectation that the output on the external display will match the built-in LCD. 

Primer: Connector Alphabet Soup

On laptops, some form of multiple display capability is almost a given, with the integrated flat panel and the ubiquitous external display port (VGA or DVI, perhaps via a dongle on some thin-and-light models) and possibly analog TV-out (to S-Video, composite "RCA", or component video, possibly via a dongle and/or adapter), as well as docking stations available on some models to provide yet another port or two.  In the desktop space, for some time now it has been common for even low-end discrete grahics cards to support multiple displays, commonly with TV-Out and either one VGA port and one DVI port or a pair of DVI ports.  For simple simultaneous display, video splitter devices or cables might provide further options, depending on the connectors on the available display devices.  As ever, there are many ways to skin a cat.

Video Card Interfaces

If a desktop PC's existing display adapter (whether integrated or discrete, on-board or an add-in video card) does not already support multiple displays, installing an appropriate video card is an option.  Before acquiring a card, verify the type of slots available in the PC to select the appropriate interface: PCI Express, AGP, or PCI.

PCI Express

PCI Express (also PCI-E or PCIe) is the current standard most common in new PCs and video cards.  Slots and connectors are of varying lane widths, with high-bandwidth x16 being typical for video cards, although some x1 cards are available.  Cards with narrow x1 connectors will fit in wide x16 slots, but not vice versa.  Cards and slots for the newer, faster PCI Express 2.0 standard should be compatible with their version 1.x counterparts, though with reduced bandwidth.

AGP

AGP was the previous standard interface for video cards, still in use in many existing systems.  While new AGP video cards are still available, they are growing less common as this older standard gives way to PCI-E.  AGP served as a dedicated video interface complementing PCI, typically with only one AGP slot in a system, if any was provided at all.  Different versions of the interface were introduced over time - specification 1.0 from 1996 at 1x and 2x speeds, 2.0 from 1998 at 4x, and 3.0 from 2002 at 8x - with some limits to backwards and forwards compatibility.  It is possible for an ancient system and a new card (or vice versa) to be incompatible depending on the voltages supported by each (3.3 V or 1.5 V).  Variations in the physical connector itself were specified to prevent electrically incompatible components from being connected, with cards keyed so that they could only mechanically fit into compatible slots.  Nonetheless, non-compliant cards and slots seem to exist which do permit electrically incompatible cards and slots to be connected, possibly resulting in equipment damage.

PCI

PCI is perhaps the lowest common denominator among these interfaces, existing as a general-purpose interface prior to (since ca. 1993) and concurrently with AGP and even PCI-E (in the latter case, provided for backwards compatibility with 'legacy' cards on some newer systems).  While generally lower in performance than the alternatives, it offers the advantage of being nearly ubiquitous on older and newer systems alike.  Even after AGP had become the dominant video card interface, many lower-end systems with on-board graphics did not provide an AGP slot.  Relatively modern PCI graphics cards are uncommon but remain available as upgrades to older systems.

Random Video Card Notes

Some video cards are both hot and power-hungry when they run, which might be worthy of further research before a decision is made.  If a video card is added to a system with on-board graphics, it may be necessary or desirable to specify which display adapter is to be initialized first or to disable the on-board graphics entirely.  Such settings are very much system-specific and may or may not be available as obscure BIOS options (e.g., "Init Display First") or even by cracking open the machine and setting a jumper switch.  Finally, if the goal is to output the same content simultaneously (in "clone mode") to multiple displays, multiple display adapters (e.g., two video cards or on-board graphics and video card) are unlikely to work transparently.

PC Display Connectors

In PC displays, we find ourselves still in the midst of another one of those awkward interface transitions that seem to drag on for years.  The traditional analog VGA connector has been supplemented, if not quite yet supplanted, by the digital DVI connector.  Newer external display devices often support both.  Note that not all DVI connectors are created equal, as there are a number of variations (see images).  A DVI-I connector integrates digital and analog signals and can be mated with a VGA connector by means of a simple and commonly available DVI-to-VGA adapter or adapter cable.  A DVI-D connector is digital only, with fewer pins, and will require a less common, more complex, and probably more expensive digital/analog converter.

For the adventurous, I have seen various splitter cables and devices sold online for specialized needs, but I do not have personal experience with them and cannot vouch for them.  Y-cables exist to split a DVI-I integrated digital/analog output port into a digital DVI-D connector and analog VGA connector.  Y-cables also seem to be available to split a Dual Link DVI output port into two single link connectors.  VGA and DVI splitter boxes can be obtained to replicate the output of one port across multiple displays.  Again, I cannot vouch for such devices, but I can imagine that they might cause headaches if used with a heterogeneous assortment of displays supporting different ranges of resolution and refresh rates, and I am inclined to wonder how well the VGA splitters support DDC.

TV-Out

As for televisions, various analog connections (RCA/Phono Composite Video, Component Video, or S-Video) may be supported by a TV-Out port on some computers, but this is a decidedly unsatisfactory option if one needs sharp high resolution output (e.g., with legible text).  Specific capabilities will vary according to the display adapter and associated driver in use, but resolution will be low, and higher display resolutions, if supported, will likely result in an ugly blurred flickering interlaced off-color mess after conversion to NTSC, my regional analog TV standard (like my experience outputting a Windows Vista Desktop via S-Video at an unusually high 1024x768 from an HP tx1000 tablet with its integrated NVIDIA GeForce Go 6150 graphics).  Analog TV-Out only delivers reasonable quality with a low display resolution.  Newer digital televisions may include more computer-friendly inputs which make for a better choice:  VGA, DVI, and/or HDMI, the last of which may be fed via an adapter from a DVI source (although with HDCP DRM restrictions potentially blocking some content).

User Interfaces: The More, The Merrier?

Standard Windows Display Settings

Microsoft Windows XP

Assuming the hurdle of physically connecting the display(s) has been overcome, further configuration may be necessary for the multiple displays to behave as desired.  Windows XP has some built-in controls for managing multiple displays, but these are geared towards extending the desktop onto additional displays rather than having both displays show the same content.

• Right-click an empty part of your desktop to bring up a pop-menu and choose 'Properties' from the pop-up menu.  (Alternatively, go to the Control Panel.  If in 'Category View', > 'Appearance and Themes' > ('Pick a task...' > 'Change the screen resolution'), or ('pick a Control Panel icon' > 'Display').  If in 'Classic View', > 'Display'.)
• This should bring up the 'Display Properties' dialog box.  Select the 'Settings' tab if it's not already selected.

If you have multiple display connectors of which Windows is aware, you should see multiple numbered monitor icons in the box under "Drag the monitor icons to match the physical arrangement of your monitors" (where you can do just that), as well as corresponding entries in the drop-down menu under "Display".  You can use either to select a monitor.

An inactive display will have a faded icon (and display "Not Active" if moused over).  You can activate it by right-clicking the icon and checking 'Attached', or by selecting it and checking "Extend my Windows desktop onto this monitor" (and clicking 'Apply' or 'OK' as needed, of course).  If all has gone as intended, you should see a blank desktop on the secondary display.  If you're confused as to which display is which, click the 'Identify' button, and the display number should appear in the center of each display.  Note the relative locations of the monitor icons.  You should be able to switch between or among your displays by moving your mouse pointer off-screen in the appropriate direction.

This is about as intuitive as Windows XP gets, and it's a standard part of the OS. You can change screen resolution and color depth independently for each display, designate a given display as primary by checking "Use this device as the primary monitor", available only when the display is active, etc.  Play with it - it's fun.

Microsoft Windows Vista

Always zealously endeavoring to fix what ain't broke, Microsoft has moved things around a bit in Vista and changed some of th e terminology.  If you're stuck with Vista (my condolences), you can access the 'Display Settings' dialog box as follows:

• Right-click an empty part of your desktop to bring up a pop-up menu and choose 'Personalize' in the pop-up menu.  (Alternatively, go to the Control Panel.  If in 'Control Panel Home', > 'Appearance and Personalization' > 'Adjust screen resolution'.  If in 'Classic View', > 'Personalization' > 'Display Settings'.)

If you have multiple display connectors of which Windows is aware, you should see multiple numbered monitor icons in the box under "Drag the monitor icons to match your monitors" (where you can do just that), as well as corresponding entries in the drop-down menu therebelow.  You can use either to select a monitor.

An inactive display will have a faded icon (and display "Not Active" if moused over).  You can activate it by right-clicking the icon and checking 'Attached', or by selecting it and checking "Extend the desktop onto this monitor" (and clicking 'Apply' or 'OK' as needed, of course).  If all has gone as intended, you should see a blank desktop on the secondary display.  If you're confused as to which display is which, click the 'Identify Monitors' button, and the display number should appear in the center of each display.  Note the relative locations of the monitor icons.  You should be able to switch between or among your displays by moving your mouse pointer off-screen in the appropriate direction.

This is about as intuitive as Windows Vista gets.  You can change screen resolution and color depth independently for each display, designate a given display as primary by checking "This is my main monitor", available only when the display is active, etc.  Play with it - it's fun, arguably even more fun than in XP.

Vendor-Specific Controls

Unfortunately, playing with the standard Windows display settings does not reveal options for having both monitors display the same output.  Instead, this requires user interface controls that vary widely depending on the type of video card (chipset model and manufacturer) and the drivers and software utilities installed.  Each graphics chipset manufacturer (e.g., ATi/AMD, Intel, NVIDIA) has its own proprietary UI (User Interface) for manipulating multiple displays and other advanced settings, with little apparent concern for maintaining consistency from version to version.  System, motherboard, or video card manufacturers might further add their own proprietary customizations and/or utilities in an attempt at "value-add" (or perhaps "vendor lock-in").  Depending on your system's history, you may need to hunt down and install an appropriate driver and/or utility from the manufacturer of your system, motherboard, chipset (core logic), video card, and/or GPU.  If you're lucky, your system may "automagically" default to the multiple display mode you desire or detect a newly connected additional monitor and prompt you for your preferences.

While each system configuration may have its own quirks, there are some general commonalities in where to look for proprietry display setting controls.  For some display drivers/utilities under Windows 2000/XP, clicking the 'Advanced' button under the 'Settings' tab in the aforementioned 'Display Properties' dialog box should bring up yet another dialog box that may have a tab bearing the GPU manufacturer's name and/or log and/or the model name of your GPU, or something else along those lines.  Otherwise, your GPU chipset manufacturer might have generously graced your control panel and taskbar's notification area with an icon bearing its logo (and perhaps its name, in a tooltip).  If you find it, hunt for some button, tab, or menu item with a name suggesting that it might contain options pertaining to the management of multiple displays.  Keep an eye out for a setting to "clone" displays, which ATi/AMD and NVIDIA both currently seem to agree is the appropriate term for sending the same output to both monitors.  Many systems will clone by default if multiple monitors are attached.

NVIDIA Examples

The following is an example of some of NVIDIA's vintage 2003 display controls.  Specifically, this image was captured from a Toshiba Portege M200 Tablet running a model-specific NVIDIA Detonator 46.44 driver from Toshiba under Windows XP.  Assuming a similar setup, this can be accessed as follows:

• Right-click an empty spot on the desktop to bring up a pop-up menu.  Choose 'Properties'
• This should open a 'Display Properties' dialog box.  Click the 'Settings' tab if it's not already selected, and click the 'Advanced' button towards the bottom right.
• Another dialog box should open.  Click the tab with the funky green NVIDIA logo if it's not already selected.

You may then try to decipher the various settings and experiment by clicking various intersting places and the 'OK' or 'Apply' buttons as needed to effect any changes made.  The above example is set up with multiple monitors in "Clone Mode", sending the same output to both displays.

A more recent example demonstrates that our "innovative" friends at NVIDIA have worked hard to refine their user interfaces, not content to simply rest on their laurels (or to leave well enough alone).  This is from 2007, specifically using a ForceWare 169.21 driver downloaded from NVIDIA on Windows XP with a low-end video card featuring an NVIDIA GeForce 6200 GPU.  Assuming a similar configuration, it can be accessed as follows:

• Right-click an empty spot on the desktop to bring up a pop-up menu.  Choose 'NVIDIA Control Panel', OR
• Look for an icon with the funky green NVIDIA logo in the System Notification Area towards the right of the taskbar, expanding if needed.  Mousing over it should display the tooltip 'NVIDIA Settings'.  Click this icon to bring up a pop-up menu, and click 'NVIDIA Control Panel', OR
• Open the Windows Control Panel.  If in 'Category View', under 'Pick a category', go to 'Appearance and Themes', then, under 'or pick a Control Panel icon', choose 'NVIDIA Control Panel'.  If in 'Classic View', simply go to 'NVIDIA Control Panel'.

(Click for larger image) 

The above is the 'Advanced' view (menu bar at top of window > 'View' > 'Advanced'), which exposes a few more options than the 'Standard' view.  Regardless, in either view there should be an (over)abundance of options to explore, although the availability of some options may vary depending on the exact system configuration.  This example is also set up with multiple monitors in "Clone Mode", sending the same output to each display.  Note that the order of the displays in the drop-down menu under '2. Select the displays you would like to use' is significant.  In clone mode, the dual monitors are treated as a single display under the standard Windows display settings (for resolution, color depth, and monitor refresh rate) rather than independently as primary and secondary displays.  Nevertheless, the two displays may not be exact clones, with output such as copy-protected video content appearing only on the display considered "primary" by the display driver.  In this case, such troublesome output will appear on the monitor listed first in the drop-down menu selection, and the destination can be changed by selecting a different order (i.e., "Monitor B + Monitor A" rather than "Monitor A + Monitor B").

Laptop Display Switch Hotkeys

A notebook might save you a bit more trouble by having a hotkey combination to quickly switch displays from internal to external to both (cloned).  This varies from manufacturer to manufacturer (and possibly model to model), but seems typically to be some combination of the Fn (Function) key (typically towards the bottom left of the keyboard) and one of the top-row function keys (F1, F2, F3...F12).  The proper key combination might be most easily determined by scanning the keys for a cryptic icon resembling a pair of stylized screens, or something similar.

Example Notebook Display Switch Hotkey Combinations

(I apologize to anyone who might actually read this insanely long page.  It's is still a work in progress.  I have more random nonsense to add, and I'll probably end up breaking it up into multiple pages, as time and energy permit.)