Moving files from one partition to another on an SSD

Each partition has it's own, independent file system. If you move a file within a partition, the file system can simply rewrite the reference to that file.

But when moving a file between partitions, the file system on the destination partition doesn't know anything about the new file - there is no reference to adjust. Furthermore, each partition will have it's own physical area of the drive to itself, so the file must be copied to the new partition, then deleted from the old partition.

Copying large files in this manner is often slow, probably even noticeably for some SSDs, because the drive is thrashing between reading one area and writing to another.

Partitioning a hard drive actually designates physical regions for each partition. The file is being moved from partition 1 (physical region 1) to partition 2 (physical region 2). When you move a file from partition 1 to elsewhere in partition 1 (another folder), the file is already in the correct physical region, so only the reference to it changes.