Although the program is designed for Windows 98, 2000, and XP; I feel it is most effective with windows 98, as 98 is more prone to loose memory here and there and crash quite a bit. Speed Up My PC does a fine job of freeing up system resources and bandwidth. With the aid of this program I was able to knock over 10 seconds off of my startup time, which was quite nice. Another interesting use to note is the programs ability to help in the detection of spyware. It is these features that make this one of the best pieces of optimization software on the market today.