I have recently installed Windows 7 Ultimate x64 with Service Pack 1, coming from Vista (in which I had no problems). After the installation, the first thing I did was install the graphics card driver for my AMD Radeon HD 6870 1GB card. I then noticed that when I drag windows around the desktop, scroll through windows, and especially drag windows from the secondary monitor to the primary, there was very noticeable lag. However, there was no lag in games – just the Windows desktop and its windows. This was a completely fresh install. I have dual monitors – the primary is a 19″ widescreen Acer X191W, and the secondary is a 15″ Sony LCD. I am using them in extended desktop mode.
What happened at first was Windows locked the primary monitor to 75Hz, and would not let me change it to 60Hz. For some reason the first time I installed the video drivers, I think there was a conflict with the default Windows display drivers, causing my main monitor to be stuck at 75Hz. I had to uninstall and wipe the display driver to reinstall it, after which the option to set it to 60Hz appeared. I used ATIMAN Uninstaller to wipe the driver. After setting the display to 60Hz, the lag disappeared completely.
So it seemed there was a conflict somewhere with my specific hardware configuration that caused lag when two monitors were set to different refresh rates. However, then I tried to recreate the problem on a different system. This system has a Radeon HD 4870 and different dual displays. It had the same problem when one of the monitors was set to refresh at 60Hz and the other at 75Hz. And again, putting them both to 60Hz resolved the lag issue.
I could not find any information about this issue online. It can’t be the monitors as between the two systems there were four different monitors that had the same problem. It can’t be the hardware, because my computer has a 6870 and the other has a 4870. It can’t be interfering software, as this was a clean install of Windows. It has to be either the AMD driver, or an issue with Windows.
The point of this post is to let people know how to fix this issue, as well as ask if anyone else has experienced this, especially with a different graphics card. It took me two weeks to find the cause of this. I haven’t found anyone online with this issue. Both the video cards I tested should handle different refresh rates without a problem. Although I have fixed the issue, I still want to know what caused it.