Drives, files, and fragmentation
A physical disk can contain several volumes, such as C: and D:. O&O Defrag generally works on these Windows volumes. Two drive letters can therefore share the same physical hardware.
File fragmentation and free-space fragmentation
Windows stores file data in allocation units called clusters. When a file occupies several separate areas, it is fragmented. A fragment is a continuous extent of that file's stored data.
Free space can also be split into many areas. Joining file fragments and consolidating free space are different objectives. Choose a method according to the result you need.
Deleting a file increases available capacity. Defragmenting it changes its placement and normally does not increase free capacity. Cleanup and optimization solve different problems.
HDDs and SSDs
An HDD uses mechanical movement to reach data. File placement and extra seeks can affect performance. An SSD has no read head; sorting files by name or date does not provide the same benefit and can cause additional writes.
O&O Defrag identifies the media type and uses it in its recommendations. If a controller or enclosure reports the wrong type, correct it in Drive detection before making a method decision.
Fragmentation statistics
Read a fragmentation percentage together with the analysis date, file information, and recommendation. It is not the percentage of time your computer wastes and is not a speed measurement.
Different settings and product versions can count fragmentation differently. In particular, the ROI reporting option can omit fragmentation that SOLID deliberately leaves untouched. Compare results from the same version and settings.
Files that may remain fragmented
Some files are locked, excluded by rules, part of file-system metadata, too large for available working space, or below the ROI benefit threshold. Normal Windows operation can also fragment files again after an optimization.
FileInspector helps distinguish these cases. Boot-time optimization provides a separate environment for eligible files that cannot be moved while Windows is running.
Storage systems and virtual drives
For RAID, virtual disks, and shared storage, Windows may expose a logical volume while the storage controller handles physical placement. Drive detection and supported operations depend on that stack. Coordinate scheduled work with backups and other storage maintenance, especially when several volumes share one physical disk.
Free working space
Optimization needs space to move data. Leave sufficient working space for the files you want to optimize. File sizes and the largest contiguous free regions affect which files can be moved and how many passes are needed.
If large files remain fragmented, inspect available space and file rules before repeating a full run. Cleanup frees capacity; optimization normally changes placement without freeing capacity.
Shadow copies
Moving data can increase copy-on-write storage consumption where shadow copies are in use. Review free space and snapshot retention before a large rearrangement. Disabling System Protection can remove restore points, so it is not a routine prerequisite for optimization. Coordinate maintenance with the backup policy in use.