Thanks Nick_N.2 more Q's:1.O&O complete/name - How did you know about the technical differences between versions 8.x & 10 in paricular the defferent handling of file slack etc.?ie. Was it relased available to the public or as inside information from the company?I understand 'slack space' to be the unused space on a disk between the end of a file and the end of the cluster it resides in.Eg.a) a 1Kb file in a 4Kb cluster (default NTFS allocation unit size) leaves 3Kb of slack space.Eg.:( In windows file explorer; look at the properties of a 1Kb file you can see 2 figures 1='Size' 2='Size on disk'. The difference is the amount of slack.Most (if not all) defrag. applications I know of process at a minimum granularity of the file cluster size. (eg. 4096bytes per cluster, 512bytes per sector on a default NTFS partition). And simply re-assembles the clusters of a file together in a contiguous order. And therefore file slack is not even considered.There inevitably will always be some slack at the end of every file in the last cluster it occupies, and this fact cannot be controlled other than changing the cluster by re-formatting.Per your statement - "When O&O version 10 runs a COMPLETENAME defrag it leave space in the sectors between the files and does not compact them closely together....";I only understand you meaning O&O inserts 1 or more 512byte sectors between the end of one file's last cluster and the start of the next file's first cluster - correct?It doesn't make sense to me!!! And I'd like to confirm it with O&O directly.** Does the app. 'Diskeeper' have a similar choice of defrag methods?It didn't the last time I evaluated it (2003~2004).2.Now my 2nd issue Re. specifying a partition's cluster (allocation unit) size by the format command...With NTFS, disk I/O reads & writes at the sector & cluster level. The default cluster size for windows-XP being 4096 bytes/512 per sector.In the case of MS-FS which uses 1000's of files many of which are less than 4096bytes size, there's a lot of file-slack within clusters and time wasted reading unoccupied sectors!!Would it be a further improvement for MS-FS to format the partition where it's installed to a smaller cluster size eg. 512, 1024 or 2048 bytes, therefore making the actural reading of those smaller files off disk faster?*** FOOD FOR THOUGHT ***Mike.

There is no food for thought Mike1. O&O v 10 will allow drive fragmentation v8.5 and 6 wont. I don