Link (via Engadget)
1. Single-Pass Mode (Standard and Pro Model)
A single data pattern is written one time across the whole disk, deleting blocks including partitions and Host Protected Areas. Verification is also done after a single pass.
2. Multi-Pass Mode (Pro Model only)
The Pro model offers the ability to perform multiple passes. Why? Some studies show that there may be ways of recovering bits of data even after completely overwriting everything on the drive. We believe the laboratory required to actually pull off such a feat would cost millions (if not billions) of dollars. However, if you must convince someone that there's no way data can be recovered, a pro model with the multi-pass feature is for you.