From: Tape

19mm is 3/4 inch helical scan tape.  Two varieties exist, D1 and D2.
Both originated from broadcast and/or data recorder applications,
where the data/signal was analog in nature.  They have been modified
for digital use, with error correcting capabilities added.

Data rates are in the 8-45 MByte/sec range, with storage capacities
in the 25-175 GB range in physically different size cartridges with
different length tapes, but all fitting into the same tape drive unit.