DVHS is a digital recording and playback format for High Definition material. It's based on the existing 1/2" VHS-sized cassettes.
D-VHS is a digital video format developed by JVC, in collaboration with Hitachi, Matsushita and Philips. It uses the same physical cassette format and recording mechanism as VHS, and is capable of recording and displaying both standard definition and high definition content.
HD content is stored at 28.2 Mbit/s, while SD content can be stored at bit rates from 14.2 Mbit/s down to 2.0 Mbit/s. The most capacious D-VHS cassette can store 3.5 hours of HD content and between 7 and 49 hours of SD content, equivalent to 44 gigabytes of video data. This cassette contains 1378 feet (420 m) of tape, equivalent to a 3.5 hour NTSC or 4.9 hour PAL VHS cassette.