DVR+ (CM-7500) out of the box will record up to 2 hours of High Definition programming.
DVR+ (CM-7500) with a 500GB external hard drive will record up to 90 hours of High Definition programming.
DVR+ (CM7500) with a 1TB external hard drive will record up to 180 hours of High Definition programming.
HD content uses much more data space than SD content.
Since each channel transport stream bit rate can vary from TV Station to TV Station, it is not possible to provide a definitive answer.