Information on a hard drive is stored sequentially, in that files are stored one after the other with no spaces between them. When you need to increase a file's size, it would be ridiculous to shift all files following to make room, files are modified all the time, should a hard disk need to adjust the location of numerous files at every write, performance would be exponentially reduced and the drive would be under (almost) constant load. Same can be said for file size reductions, the files following would need to fill the gaps every time something is erased. Seeing as constant adjustments are impractical, information added onto a file is placed at the end of the data (or in a blank space), this separation is known as a file fragmentation. As aforementioned, the spaces arise when a file is deleted. Rather than take the unpractical on-the-fly approach, we have defragmenters...which take care of the accrued splits and spaces. Recent evaluations have found minimal to moderate fragmentation to not effect performance tremendously; however, serious fragmentation can be problematic (See Maximum PC; June 2008).