Another one from Jim Allchin: If there is one thing that can really help applications on Windows Vista run better, it's memory. When comparing the performance of Windows XP and Windows Vista on a PC with 1 GB of main memory, Windows Vista is generally comparable to Windows XP or faster. However, we also know that in some cases, on PCs with 512 MB of main memory, applications on Windows XP may seem more responsive. Why? Mostly because the features in Windows Vista use a bit more memory to do the things that make it so cool, like indexing your data, keeping the fancier AERO UI running using the desktop window manager (DWM), etc. The less memory in your machine, the more often the OS must randomly access the disk. This slows system performs in cases where your applications just barely fit in memory on Windows XP but not quite in Windows Vista.

We redesigned the memory manager in Windows Vista so that if you give the system more memory, it uses that memory much more efficiently than previous operating systems via a technique called SuperFetch -- part of Windows Vista's intelligent heuristic memory management system. And so Windows Vista on a PC with even more than 1 GB of primary memory (say 2 GB) will generally outperform Windows XP on that same machine -- especially once you have been using the machine for some time because Windows Vista learns what you do the most often and optimizes for this.