+ 0 Votes If you don't defrag for up to 6 months, all I can say is... OldER Mycroft 6 years ago You are one light-user.I tend to run a defrag analysis every weekend, then go with what the program advises.Almost every time you write to a hard disk, you create a degree of fragmentation since the write head tends to drop bits of the file wherever there is space, rather than look around for a space that is big enough.By not defragging you save the disk-thrashing that defragging involves - only to generate disk-thrashing as the read head searches for all the bits of the file it is looking for."I usually do it when file fragmentation rise to like 20% or disk nearly full"If you wait until your disk is nearly full ( of what: files or fragmentation ?? )you run the risk of the defragmentation failing due to insufficient free space for the bits of the fragmented file to be reconstituted, thereby put back together again.It is the hard drives that tend to fragment - it does not matter what operating system is running on them. I used to defrag the hard drive on my Amiga 4000, and it's OS was closer to the MAC than the PC.