[lug] 8mm video vs. data tapes

[Tkil]

>>>>> "Wayde" == J Wayde Allen <wallen at lug.boulder.co.us> writes:

Wayde> For analog recording the magnetic variation in the tape needs
Wayde> to be at a minimum in order to keep the noise level down.  The
Wayde> tape also has to be able to record relatively small magnetic
Wayde> fluctuations.

Wayde> Data on the other hand is a fairly large level signal, is
Wayde> relatively well correlated making less susceptible to random
Wayde> noise, and has built-in error correction.

Is this still true with some of the fancier encoding methods that are
being used on magnetic media?  From a discussion of PRML in:

   http://www.usenix.org/publications/library/proceedings/sec96/full_papers/gutmann/

it seems that (at least on hard drives) it's no longer an obvious
string of ones and zeros (and it hasn't been for a while).  The author
of the above paper compares it to the symbols used in modern modems
(where you might have only a 4800 baud signal, but you're transferring
33600 bits per second -- implying 7 bits per symbol, or 128 distinct
symbols.)

So "data tape" might not be so different from "analog tape" after all.
[ObConspiracy: I doubt that we'd ever get a straight answer from a
tape manufacturer, however, since they can make more money by
splitting the market and charging a premium.]

t.