QAM allows reception via cable of unencrypted digital channels, in my town this allows all the network HD channels to tune in, ABC, PBS, CBS, NBS, Fox.
I highly recommend the Sony DHG-HDD500 or 250 HD DVR models. I have 2 of the 500 models (500gb each), blows away the old school cablebox HD DVRs. Uses ota, cable, or cablecard, my 500s each hold 40 hours of HD programming/200 SD programming. They were discontinued but are numerous on ebay (250 model) and very much in demand now.
I use a Sony DVD recorder RDR-HX715 with 160gb hard drive to record SD programming too.