The S3 which uses a 160GB internal, the TCD652160, or HD, has a list of a very few WD bare drive numbers, and the drive inside the external eSATA enclosure has to be on that list, and only 500GB and 1TB drives are on that list. When the original S3, the 648, came out, the option to add an external hadn't been added yet, even though there was an eSATA port on the motherboard. Somebody figured out how to enable it, and so TiVo found themselves faced with lots of 648s out there with all sorts of different brand and size drives attached externally. So they couldn't include conformance to the list on that model when they updated the software because it would have "broken" so many units. (Maybe some of the "hackers" over there at the other "site which may not be named here" figured out a way around the list for HDs and HD XLs, but for your average home gamer the 652 and 658 have to use one of the WD externals with the TiVo logo on the retail box.) So much simpler to just slap a WD20EURS in them.