Adaptec ships **different** versions of the 2940UW and 3940UW accelerators cards for the Mac and the PC. Pro Tools|24 users need to ensure that they buy the Mac-compatible version of the Adaptec SCSI accelerators. The PC-compatible cards will not work with the Macintosh and Pro Tools|24. The Mac-compatible cards are called "Power Domain 2940UW" and "Power Domain 3940UW". It is the words "Power Domain" which differentiate them from the PC versions, but this might not be clearly marked on the packaging.