GeForce 6600GT: The GeForce 6600GT is the oldest graphics card being tested in this article. The 6600GT is from the NV40 family and is clocked at 500MHz with 128MB of GDDR3 video memory at 1.0GHz. The GeForce 6 series was introduced in 2004. The GeForce 6 series is also the oldest generation of graphics processors still supported by the mainline NVIDIA binary Linux driver, while the older generations are now on legacy branches.
Unfortunately with the latest binary driver, while OpenGL acceleration was exposed and other functionality working on first glance, this graphics card had issues with the binary blob in shader-based games (it looked like the GPU would hang upon compiling shaders). When it comes to the open-source drivers, it has been hit or miss depending upon the software configuration. Years ago the GeForce 6 series support was great (and I had even provided a GeForce 6600GT to a Nouveau developer years ago), but I have had KMS problems with the GeForce 6600GT on many kernel snapshots in the past year or two. With the Linux 3.2 kernel, KMS was working for the GeForce 6600GT but the graphics card was unstable when it came to running OpenGL tests.
The GeForce 6 series support in Nouveau has regressed to the point that even using the Unity desktop with Compiz window manager is unusable. Above is a video I quickly recorded from the Linux kernel and Mesa Git showing the "out of the box" performance with a measurable lag when moving around windows, etc. It's with GPU hardware acceleration, but worse than when using the LLVMpipe driver.