The registry records the relationship between hardware, memory space, and addressing. It contains information and settings for all the hardware, software, users, and preferences of the computer. Whenever you make a change to the Control Panel settings, file associations, system policies, or installed software, the changes are reflected and stored in the registry. The operating system continually references this information during its operation. you can see What is Registry? http://downloadlk.net/whatisregistry.htm
However, a centralized registry system presents some problems as well. The registry is considered a “single point of failure” – modifications can lead to disrepair. The resulting damage could range from poor performance to not being able to boot up your computer. In these most extreme cases, data could be unrecoverable and a full re-installation of the operating system would be required. You have to re-install your system always. To determine if your system is in fact running slow because of problems in your registry, you will need to run a Registry software such as http://downloadlk.net/themosteffectiveregistrycleaner.htm .This easy to use program will perform a deep scan on your computer and will report back on any issues or problems it finds for you at no charge – which means you can figure out what is wrong.