The Operating System can affect Frame rates when trying to render an object in realtime 3D.
Various features of of operating systems (or lack of features) can drastically effect a computer’s ability to render in realtime. Features such as preemptive multi tasking vs. cooperative multitasking, virtual memory (or pageing files.)
Some programs duch as DVD players will bypass the graphics subsystem and send data directly to the graphics processor in order to minimize dropping of frames during playback. Ever tried to take a screen capture/dump of a DVD movie frame? Can’t be done… This has less to do with copy protection, and more to do with where the data is being sent.
Anyway, back to Frame Rates…
If an OS includes more advanced memory management (both virtual and static) and more advanced graphics models (OpenGL or Apple’s Quartz rendering layer, etc.) you will see improvemnets in your frame rates but you can still bet that the graphics data will flow through the OS (to be dolled out to the GPU probably) at some point or another. As the data passes through the OS, it will saturate any of the OS’s bottlenecks. A truly optimized (for graphics) OS will be certain that there are no bottlenecks on the way to the GPU.
In short you can have the fastest, hot diggityest GPU on the planet, but if you don’t have an OS that can keep feeding it data, it will starve… and you will see frame drops.
Here is a little test I did…
Using two identical Mac PowerBook G4s each with 8 MB ATI Rage 128 cards, I get the following results.
Running OS X 10.1.4
Running OS 9.2.x I get the following