"That means, at least in theory, a system upgraded from XP to Vista shouldn't end up as bloated and sluggish as a PC upgrade from, say, Windows 98 to Windows XP (notwithstanding the bloat that Vista may or may not come with, depending on your opinion of the new Windows). Could that be true? Has Microsoft invented an upgrade process that doesn't hopelessly clog your system's arteries with virtual cholesterol? To find out, we chose an innocent system that's led an unassuming life as the main machine belonging to a former freelance journalist, a part-time game reviewer. Then we pretty much beat it over the head with Windows Vista Ultimate. In the process, we took a chunky batch of performance tests to see how the computer reacted to a Vista upgrade, and compared that to its experience with a fresh Vista installation."To a geek like me, the idea of an in-place upgrade (installing one OS over another) is possibly the worst idea possible for a computer. A clean install is the only type of OS upgrade that I've ever performed. It seems, however, that with Vista Microsoft has taken steps to essentially eliminate the problem. The article is a must-read if you're concerned about the whole upgrade/full version issue.