Interleave factor is a term describing the ratio of physical disk sectors on a hard disk that are skipped for every single one sector that is actually used for write operations on the disk. It’s expressed as a ratio – so, say, a 5:1 interleave. That’s quite high, but a 5:1 ratio would mean that one sector on the disk is used for writing, then five are skipped before another one will be written on, and so on.