Start with a fresh Windows XP install. Boot time is maybe 30 seconds, and Internet Explorer launches instantly. Now install a bunch of software on it, and an antivirus. From time to time, replace one piece of software with another. Fill the hard drive about halfway full with personal data. Install all the various updates that Windows won't be secure without. Keep it running for a year or so... Eventually (in my experience) you'll have a Windows XP install that boots in 80 seconds, and takes 20 seconds and lots of hard disk grinding to launch Internet Explorer. Apparently this is popularly known as "Windows rot." There are several things I know from personal experience are not the cause, or not necessarily involved: - The indexing service - Too many temp files - Accumulated junk in the registry - Filesystem fragmentation - Registry and pagefile fragmentation - Physical hard drive problems - Preinstalled OEM software - Third-party autoruns and services - Malware Generally it seems that the OS should by rights be snappy, but is nonetheless outperformed by Knoppix on a live CD. Everything checks out as okay, but Windows remains demonstrably and measurably slower than it should be. Does anyone here know what factors are actually involved in this problem? Assuming that it exists universally, and is not a function of some exotic driver issues on certain hardware, or something like that?