When I dual-boot into Windows XP, the defrag results are different from Windows Vista. Why?
The fact that you can see different levels of fragmentation from Windows XP and Windows Vista is not necessarily unexpected. The reason is that Windows XP and Windows Vista use slightly different algorithms for determining which files are fragmented and which files can benefit from fragmentation. On Windows XP, any file that is split into more than one extents is reported as fragmented and the Disk Defragmenter will try to move it. On Windows Vista, we want to take advantage of the fact that the biggest performance gain from defragmentation is when you combine files in “big enough” extents. “Big enough” here is 64 MB, which happens to be about the extent size for which the disk-seek latency starts to become negligible compared to the latency associated with sequentially reading the extent. This means that the performance benefit of coalescing two extents larger than 64 MB is minimal while the I/O load and free space requirements are significant. The different levels of fragmentation th
