One of Vista's best new features is a drastically overhauled display driver model. Based on analysis from Microsoft's Windows Error Reporting data, most of the BSODs in Windows are caused by bad drivers, and a large percentage of those bad drivers are graphics card drivers. So the WDDM aimed to solve that problem by building a much more robust display model which took over large operations that were previously required at the driver-level.
The changes have saved my butt on plenty of occasions. Before, when a graphics card driver crapped out, so did the rest of your system. I've lost data many times because my Nvidia card decided it didn't like an instruction that was just passed in, and decided to give me the blue finger. In Vista, a failed graphics driver is no problem. The system just pauses while the driver is reset, then you session resumes where you left off. It's pretty slick.
But this newfound graphics card stability comes at a fairly hefty price. As Microsoft whitepaper on the WHDC notes, Multi-monitor scenarios have drastically changed as well. In the past, you used to be able to install more than one graphics card from more than one vendor on your system, and it would run fine. But in the WDDM, that is no longer the case. If you want to get the Windows Aero experience, you have to not only be running WDDM drivers, but you have to be running the same drivers for each card, meaning that each card has to be from the same vendor.
Microsoft's reasoning is as follows:
The use of multiple graphics adapters occurred when graphics hardware vendors did not expose multiple connectors on graphics adapters. Today, almost all modern adapters support two or three connectors such as DVI, VGA, and S-Video. Also, most OEMs are now offering SLI/Crossfire configurations that support two or more graphics adapters that could also be used to connect more than two display devices when not in SLI/Crossfire mode.
Usually, that would make perfect sense. Most graphics cards have two output ports... and SLI cards mean that if you want dual cards... they'll be the same brand, and linked together through a separate interface.
But here's the problem. There are a number of solutions out there that use emulated display drivers to do some pretty interesting things. MaxiVista is a perfect example of this. It uses an emulated display driver to shuttle your primary or secondary display data to another PC for viewing. It's like an all in one dual-monitor/KVM/presentation system. But Vista's features have severely limited their software:
First of all, we were first in finding the product name (trademark registration) ;-)
- Windows Vista unfortunately introduces some serious limitations when using multiple monitors. This limitations are independent from MaxiVista and you also experience them when using physical video cards: Windows Vista generally disallows installing multiple WDDM video cards from different vendors. This means you cannot install e.g. a ATI video card along with a nVidia card on the same PC if one of them is using WDDM drivers (more information by Microsoft). Therefore, MaxiVista can only support the classic, non-aqua display mode of Windows Vista when using legacy XPDM drivers for your physical video adapters. (Emphasis mine)
- Windows Vista generally does not allow you to log on to remote PCs using any 3rd party software "for your safety". This means, that the new MaxiVista feature to use the viewer program as a service and to log onto the secondary PC via the remote control feature does not work. This is a Windows Vista restriction, not a MaxiVista limitation.
- Windows Vista x64 disallows to install software with unsigned drivers "for your safety". As MaxiVista drivers are not yet signed, it does not work under Windows Vista 64 Bit OS.
This was really disappointing to me, as I was looking to use MaxiVista as a cheap KVM solution to manage my Windows Media Center computer from a console session. I wanted to do it this way because Windows Media Center will not let you watch TV over a Remote Desktop session, and it won't let me use another Vista Media Center PC as an Extender.
I really hope that Microsoft and MaxiVista are able to find a solution to these problems. One way would be for MaxiVista to work with AMD/ATI and Nvidia to create display drivers that work in WDDM mode and appear as Nvidia or ATI drivers. That would work around the "heterogeneous graphics driver" limitation in Vista, and allow their place-shifting monitor functionality to work. Or Microsoft could fix WDDM in Vista SP1 to re-enable these use cases.
Either way, these limitations make Vista's display improvements a mixed blessing.