http://www.cisco.com/web/consumer/support/settop_8300hddvr.html
Certain versions of the Scientific-Atlanta Explorer 8300 (the 8300 HD, 8300 MR, and 8300 HD-MR) DVRs are compatible with external SATA drives so that you can expand the amount of recordable hours of programming that can be stored. At this time there are SATA drives from Apricorn, Maxtor and Seagate that are only compatible with boxes running the SARA software. Cable companies have a choice between running their 8300 DVR boxes on SARA or Passport software. The current version of the Passport software does not support external SATA drives. Several providers currently support external SATA drives, including Time Warner and Charter. Seagate's consumer line of external SATA (eSATA) drives are supported, but its flagship Freeagent Pro drives are not compatible.