I have a WD 1TB eSATA drive (My DVR Expander WDG1S10000) connected to an HR21 and it has worked fine for over a year, except for slowing down a lot as the drive fills up. I just acquired an HR24, and when I checked WD web page, they now have a new drive called My Book AV (WDBABT10010HBK), which they claim is HR 20-23 compatible (and I assume HR24). The WD web site gives no technical info about how they differ, other than that the newer My Book has a USB port (that I do not need), and "Silkstream technology" (=???) for "smoother" recording and playback, but I have no idea whether that has any significance for DTV customers. Since I know that the older My DVR works with HR2*, that would be the safe choice, but I am wondering if the newer My Book has some technical improvements (eg, does the HD spin at a faster speed, say 10k rpm instead of 7200rpm?). Does anyone know if these two models differ, beyond the USB port and "Silkstream"? Has anyone tried the newer My Book on an HR24? ps. Just noticed an Amazon customer review of the My Book AV: "...I got approximately 60-68MB/Sec with ESATA and 27MB/Sec with USB2. It initially starts out at approximately 100+Mb/Sec ESATA and very rapidly drops to 60-68. I spoke to WD about the speed drop and they said that was normal. ..." (this customer had it connected to a "new" Toshiba laptop, not a DVR). I would have thought that 60-68 mb/s is very slow for a SATA connection.