Thanks DennisD and redhawk. There are not many defragmenters for mac because the Mac OS X is less prone to fragmentation. In fact I know only one defragmenter for mac, and I cannot use it right now because I don't have a mac system in my computer. Anyway, when I try to analyse the partition to check the defragmentation level, the system freezes at 50% - 88%.
In fact I think (maybe I'm wrong) that Windows 7 can read but not write HFS+ partitions. I barely remember that I installed the Apple Boot Camp to write, but it was so unstable that I switched to MacDrive. Or maybe Windows 7 cannot read at all and I installed the Boot Camp from the beginning.
