According to Redmond, the hotfix attempts to rectify Windows Vista not taking advantage of multiple GPUs within a system.
Via X-bit Labs: "Microsoft Corp., the world’s largest developer of software, has released a hotfix for Microsoft Windows Vista operating systems that enables work of multi-GPU technologies. Apparently, from time to time the latest operating system by the company cannot take advantage of the secondary graphics processing unit (GPU).
According to a description provided by Microsoft, graphics performance of a Windows Vista-based personal computer that uses a graphics card with multiple GPUs “seems to indicate that only a single GPU is being used”. The company also says that the same happens on computers that have multiple graphics cards.
The problem, Microsoft claims, occurs because the operating system does not forward driver-render requests to the secondary GPU. However, it is interesting to note that ATI CrossFire and Nvidia SLI technologies do work on Windows Vista, according to claims by ATI, graphics product group of Advanced Micro Devices, and Nvidia Corp. Additional details were not available at press time."
Source: GOTFRAG
Multi-GPU, I really don't need the hotfix now 