Most desktop Ivy Bridge systems won’t support three displays
Despite the fact that Intel has been banging its drums about support for up to three displays on the upcoming 7-series motherboards in combination with a shiny new Ivy Bridge based CPU, this isn't likely to be the case. The simple reason behind this is that very few, if any motherboards will sport a pair of DisplayPort connectors.
For most people this isn't likely to be much of an issue, but if Intel delivers on its graphics performance claims for Ivy Bridge, we have a feeling that at least some people will want to connect additional displays via the ports on the motherboard. Add Lucidlogix Virtu MVP software in the mix which allows for discrete graphics card signals to be routed via the motherboard display connectors when extra 3D power is needed, as well as being combined with the Ivy Bridge GPU for an extra performance boost and maybe we've found a slight flaw in the motherboard makers plans.
The issue to this specific problem is that Intel has moved away from TMDS support and towards the DisplayPort standard. However, Intel has only incorporated two PLLs and although this isn't an issue for DisplayPort connected monitors, it's a whole different matter when we're talking TMDS interfaces like DVI and HDMI, as well as of course good old analogue output. So if a motherboard maker was to make a board with three DisplayPort connectors – or one eDP interface with regards to notebooks – one of the three displays would be able to have a resolution of 2560×1600 and the other two would still be able to work at 1920×1200, due to the fact that they share one PLL.
Once we start throwing in other interfaces things get complicated, as TMDS and analogue interfaces don't like sharing PLLs. As such on a system where both the DVI and HDMI ports are used – or if the D-sub connector in lieu of one of the other two interface – no third display can be attached. The problem is that the DisplayPort interface is far from commonplace and as such most motherboard manufacturers have opted for more traditional interfaces. The chart below will hopefully help to clarify things slightly, even though it's somewhat confusingly laid out.
The entire DisplayPort issue is a bit of a chicken and egg problem, as due to a fairly limited availability of DisplayPort equipped monitors, the motherboard makers don't want to add the connector, but without the connector being more commonly available; it's unlikely that we'll see a lot more DisplayPort equipped monitors. That said, it seems like the monitor makers are finally starting to catch on and hopefully we'll see more DisplayPort equipped screens this year.
A relatively easy way around this problem would've been to take a leaf out of the graphics card makers' book, specifically Sapphire which has been making quite a few cards that implements Dual-mode DisplayPort or DP++ as it's also known as. What Sapphre has done is to take the low-cost compenents used in a passive DP++ adapter to turn a DisplayPort signal into a TMDS signal and as such an extra DVI port has been usable on its cards. The motherboard makers would be able to use the same passive components for the shared DisplayPort PLL to drive both a DVI and an HDMI port on the motherboard, without any real limiations. The shared PLL would still be able to drive DVI and HDMI displays at resolutions of up to 1920×1200 without a problem and the DisplayPort would be able to drive a 2560×1600 display.
Of course, the other approach of using DP++ would've been to include passive adapters and equipped a motherboard with mini DisplayPort connectors, something most recent graphics cards support. The end result would've been the same as above, but less space would've been taken up by the connectors at the rear of the motherboard. We're still not sure about DP++ support when it comes to the DisplayPort connector on the upcoming 7-series motherboards, but we've asked some motherboard makers about it and we're waiting to hear back from them with regards to this.
In the world of notebooks things are slightly different, as here the built in display could be connected via the eDP interface and as we have yet to see a consumer notebook with a higher resolution than 1920×1200, the issue of sharing a PLL isn't really an issue. We're not entirely sure what the limitations are on displays with a higher refresh rate than 60Hz, or for 3D content, but Intel is supporting HDMI 1.4 so we have a feeling that this would force a limitation of two displays regardless of the interface used.
Hopefully all of this has proven to be of some use. Despite the fact that Intel actually supports up to three displays via the IGP in its upcoming Ivy Bridge processors, it looks like various limitations is at least for the time being preventing three displays from being used. Once Thunderbolt equipped motherboards arrive, this could potentially change, at least if the Thunderbolt equipped motherboards also sport a DisplayPort interface as well as a DVI, HDMI or D-sub connector. At the end of the day, the easy way around this problem is to connect your displays to a graphics card, but as we mentioned at the beginning of this article, there are finally some good reasons as to why you'd want to use the ports on the motherboard.