The format the DVD Cam actually records to is 77mm DVD-RAM discs. You don´t see those much - heck, you don´t often see full-size 120mm DVD-RAM - but they´re a standard format, not a special Hitachi invention. And they´re proper read-write media, good for many, many thousands of write cycles. You´re not going to getting anything like that kind of durability out of tape.

The discs hold 1.4 gigabytes of data on each side, according to Hitachi. Hitachi are, of course, playing fast and loose with the truth; like all storage device manufacturers, they define a gigabyte as 1,000,000,000 bytes. That´s not what a gigabyte actually is. It´s two to the power of 30 (1,073,741,824) bytes, just as a kilobyte is two to the power of 10 (1024) and a megabyte is two to the power of 20 (1,048,576).