Disk Defragmentation
When computers store information on a hard drive they usually do so in a a somewhat random and erratic fashion which often results in files being split up and stored on non-adjacent areas of the hard drive. Disk defragmentaton software corrects this by re-organising the files on the hard drive such that all portions of each file are written in consecutive areas. This improves the speed of retrieving the files and improves the overall performance of your computer.
Anti-Spyware
Spyware is a type of malware (malicious software) which has the aim of seeking to extract information from your PC or to secretly download further malicious software. Even when these programs are unsuccessful at extracting information from your PC, they almost always severely impact the performance and stability of your PC. (View Wikepedia article about spyware)
Spyware and adware are technically different from viruses. Many anti-virus software programs now scan for spyware as well as viruses, but most do not do as good or complete a job at detecting spyware as software programs that are written specifically for detecting & removing spyware.
Lavasoft Ad-Aware (Free Edition) is regarded by many as the easiest to use free anti-spyware program that will scan for and automatically remove spyware infections from your computer, and one of the most effective. Download and install the free version of Ad-Aware now to scan for and remove spyware infections from your PC and improve the overall responsivenes and stability of your PC.