Causes of computer slowdown
From HelpDeskWiki
There are several reasons for computers to become unavoidably slower over time, even with a re-install:
1. Newer software often has more error-checking (due to patching security holes and so forth), more bloat, etc. As a result, they take longer to do things, and they use up more memory, even if you've just freshly installed the system -- followed, of course, by all of the updates.
2. Firewall software was just a molehill a few years ago, and anti-spyware software was non-existent. Now, they and similar stuff are considered virtually mandatory, which means more software running in the background.
3. Installing and uninstalling software almost always results in bits and pieces left behind both in the file system and in the registry. Various registry and file system cleanup programs can make a noticeable difference, but they rarely get rid of all of the junk. There is little point in removing ALL of it anyway, since the junk will be quickly replaced anyway. Also, some of it is adequately maintained automatically by the system. Windows Vista will probably significantly improve on some aspects of this.
4. If all of the bloating programs use up enough memory to force the use of the paging file, performance goes down. When enough paging occurs that it starts to "thrash", performance drops through the floor.
When Windows XP was released several years ago, the computers typically only had 128MB or 256MB of memory. This may or may not have been adequate memory at the time, but 128MB is certainly inadequate now, and 256MB is borderline. Windows XP systems should have at least 512MB now for decent performance. Brand new systems should have at least 1GB, recommended 2GB (especially for 64-bit systems), to account for future changes.
The good news is that there are some causes of sluggishness that can be dealt with. These include malware ("viruses") and legitimate programs that unnecessarily start automatically. See Windows cleanup for information on cleaning up a system so that it runs faster.
