Fragmentation occurs when data is broken up into discontinuous pieces. Though Windows 7 automatically defrags its host drive, external drives and Windows XP still require regular defragging. Here are two excellent options.
IOBit's Smart Defrag surpasses the competition in two major areas: Smart Defrag is faster, and it utilizes a perpetual defragger that runs as a background process but doesn't slow down your system.
When running in the background, the program only eats up 14MB of RAM, so it's possible to run it smoothly even on older machines. Along with quick analysis and scans, Smart Defrag boasts a scheduler and some customization features, like offering a deep defrag versus a less time-consuming one, and running at boot-up or shutdown. Overall, it's a handy defragger with plenty of options for both novices and power users. Read full review