Since Windows 95, Microsoft used what is called the 'Registry' to store important information about you're computer. The Windows registry is a database of system hardware and software settings. The Windows Operating System (XP, ME, Vista, 7) references this database continually while in operation.
Every time we install and/or remove a program from our PC, the registry is modified. But sometimes, old data is left behind, or in some way becomes corrupted.
The registry can become large, disordered, and sometimes contain errors; all of which effectively slow down a critical operation of the OS (Operating System).
If the registry is significantly bloated with errors, a registry cleaner will correct them, clean out redundancies, and re-order the information in the registry, to restore some speed to your system. As with most DeBog Slow Computer fixes, how much speed is restored depends on how bad the problem was.
There is some controversy among experts as to the effectiveness of registry cleaners. As with most slow computer problems, each one can have varied impact upon your particular computer performance. Before using a registry cleaner, be sure you have enough memory and that your fans are clean, and that you do not have Malware.
If you have installed and removed many programs AND have limited memory, it IS possible that cleaning the Registry can help.