It all starts with Windows NT, the secure Windows. NT4 added many features and a nice visual onto NT 3.5, but it crashed a lot. Windows 2000 fixed a lot of crashes, and became the stable Windows OS. XP added better multimedia, and improved ways to handle network security. After service pack 2, XP was stable and good.

Vista added many features. The problem was, it added too many new features that also slowed the machine down, a lot. Customers bought new, faster computers expecting them to be faster, but they were slower. Everything worked differently too. People were frustrated. Vista flopped.

Windows 7 design goal was "performance". Generally, the easiest way to improve how fast a system feels is to stop running programs that you're not using. Windows 7 does that. It comes with less software installed. Reportedly, it's still slower than XP, but faster than Vista.

They also fixed up a lot of interface issues and added some features.

Resource Hoggin

I don't know Vista or 7 too well, but there are a few things in Vista that would seem to cause performance problems.

* Microsoft is trying to compete with Java with .NET, which is getting better. .NET is a nice improvement on Java. The integration with Windows is deep. The current Windows religion is that all applications be run with .NET. So, they wrote a bunch of useful small apps called Windows Live Essentials, and included those applications in Vista. Rule of thumb: systems like Java or .NET run code at 50% of old-fashioned C++ code. They also tend to take more memory, even though their .EXE files are small (and even the runtime memory footprint might seem small - the code is accessing the libraries).

* Microsoft is trying to compete with Oracle and MySQL. To this end, they write apps using SQL Server Express. That includes those Windows Live programs. Running a database consumes memory and slows the computer down, even when the application is not running. (I think the big trend they wanted to foster was a move away from the JET database, which uses the popular .MDB file, and get people to install SQL Server Express and create a dependency between it and popular apps... so that eventually the sysadmins would say "let's consolidate these databases onto a dedicated SQL Server system!")

* Microsoft is trying to compete with Apple and its nice user interface. So they come up with eye-candy like Gadgets. They write these things using JavaScript and basically run in a framework similar to IE. Gadgets are inherently slow. (Personally, I think gadgets suck. A heavy, slow system that replicates the functionality of a lot of old programs. It's supposed to move web developers toward making desktop widgets... but

* Architecturally, Vista seemed to be a big break from XP - bigger than the change from 2000 to XP. They significantly altered the user's directory structure, the boot sequence, installed applications, services. Vista was such a large overhaul that there weren't opportunities to discover all the slow parts until the entire system was integrated.

There's nothing quite like running three programming platforms at the same time to slow a computer.