Questions about write blockers

Hi, I am currently preparing a review of write blocker, especially focusing on the technologies and methods used to implement write blocking. My questions are as follows.
1. Are there any good literatures (papers, technique reports, white papers, online resources) I can refer to?
2. As far as I know, the write blocker could be hardware based (HWB) or software based (SWB). The HWB sits between controller and hard drive, and intercepts commands issued by the host. The most common method used by SWB is BIOS-based (INT13h) service interface. Another SWB method is device driver based (windows). My question is are there any other methods currently being used by SWB? If so, where can their technique details be found?
3. In Unix (and its variants) and Mac, what methods or technologies are being used by SWB to implement the write blocking?

Thanks a lot!