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I have a (pretty old now) Radeon 4870 which I'm using in my windows 8 box. Its using the WDDM (1.1) drivers.

When I have a full screen app open on my primary monitor anything running on the secondary display lags badly. For example I cant play a game on my primary and watch a video on my secondary monitor. When running a non-fullscreen app on my primary there is no issue with my secondary.

Has anyone else had similar issues with WDDM/windows 8? Is this something that will be fixed by a graphics card upgrade?

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Could be related to the fact that AMD dropped official support for the Radeon HD4000 series and earlier, and will only be providing security and big-dollar-customer-mandated bugfixes going forward. I'm surprised WDDM 1.1 drivers work at all, since WDDM 1.2 was introduced in Windows 8. That could definitely have something to do with it. – allquixotic Sep 26 '12 at 14:35
In essence, there will never be an official "Windows 8" (WDDM 1.2) driver for the HD4000 series. Ever. Windows may be able to operate in backwards compatibility mode for WDDM 1.1, but when things fall back to less preferred interfaces, you're going to run into performance problems exactly like this. I severely doubt that anything short of an update to a more recent graphics card generation would fix this. The drivers for HD5000 and newer generations are completely different on Windows 8, because they provide a proper WDDM 1.2 interface and take advantage of newer hardware features. – allquixotic Sep 26 '12 at 14:36
@allquixotic ok cool I didn't realise wddm 1.1 was second class in 8 I think what you have here is the answer – Luke McGregor Sep 26 '12 at 19:34

This is not a driver issue. At all. People have reported this issue on both modern and older video cards, both on AMD and nVidia.

The problem is that Windows 8 caps the framerate to 1 or something low like that, on anything running on a second screen while a full screen application is running on the main screen.

I have no idea what causes this or what fixes it, but that's what's going on.

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I bought a new card (went from a 4870 to a GTX 660) and it no longer has this issue so i think it is definitaly (or at least in part) related to drivers/hardware – Luke McGregor Nov 25 '12 at 3:20

It appears that AMD are not supporting your card for Windows 8.

AMD drops Windows 8 support for Radeon HD 4000 and older

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up vote 0 down vote accepted

The issue is that there isn't a WDDM 1.2 driver available for my card and the OOB drivers bundled with windows only support WDDM 1.1 which isn't full windows 8 compatible as @allquixotic points out.

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