I thought you were a technical user?

The registry is that thing where Windows stores metadata about most of it's files as well as preferences for each program. It is only accessed by the OS itself or special programs that require you to go into *whatever the Windows equivalent to a -su is* mode.

The problem is that Microsoft can't seem to figure out how to keep it clean. Whenever a file is deleted, the meta data is not removed. The longer you go without paying for a program to clean it, the slower your computer gets.

Program files are deleted on a proper uninstall, but then it leaves gaps. Next time a registry entry is made it's fragmented. There is no way to defragment the registry, it has to be done at boot time and even specialized program have to.

Linux and OSX don't have a registry, they use a Keychain, which is much smaller and easy to keep clean.