tlz04 density

[Dave Olson]

In <1991May15.183245.10467 at ux1.cso.uiuc.edu> melanie at director.beckman.uiuc.edu (Melanie Anderson) writes:

| >melanie> what is the 'recording density' of a TLZ04? and length?
| >melanie> inquiring minds want to know.
| 
| thanks for the info, but that's not exactly what i asked. i already
| know i can get about a gig or so on a tape. i meant 'record density' as
| in 'bit density' as in 1600bpi or 6250bpi or 2**164b/sqmm or whatever.
| you can take blocksize * total blocks written to end of tape / tape
| length and get a rough approximation, but that ignores the inter-block
| gap and also assumes you know the length (which i can't find anywhere
| on the packaging of the maxell tapes i buy, i mean, you get all sorts
| of bizzare tape info on commercial audio cassettes like length, dynamic
| range, record speed, shell color availability, but all i get on my dat
| tapes is "Adoption of newly developed superfine ceramic armor
| metal-particle magnetic material achieves superb durability and high
| output. Reproduces excellent high-fidelity digital sound even after
| repeated use." well i would certainly *hope* so!)

There are no interrecord gaps on DAT tapes.  That isn't the
way they work.  It doesn't really matter what block size you
use, as long as it is a multiple of 512 bytes, aside from OS efficiency
issues.  (Well, if you do a LOT of small tape files, you really want
multiples of the frame size, which I don't remember off the top of my
head.)  Most of the data DAT drives have very large (512Kbyte for
the Archive, I don't  know about the TLZ) onboard buffers to
increase the amount of time they spend streaming.

60 meters is far and away the most common tape length for DAT.
This is the commonly cited 1.2 or 1.3 Gb capacity.

90 meter tapes are just starting to become available, and the
drive vendors are just completing their fullblown tests, with
pretty much uniform good results.  This is commonly referred
to as 2Gb capacity (or sometimes 8 Gb assuming an average 4:1
compression on newer drives that support compression in the
drive; 2:1 or less compression is far more realistic...).

You can get the full tape specs from the Audio DAT specs, or
from the drive manufacturers, although it helps to be an OEM
or large customer :)
--

	Dave Olson

Life would be so much easier if we could just look at the source code.