punched tape prices

[Kragen Sitaker]

Looks like punched tape is still used for some older
numerically-controlled machine tools, so it's still sold.
http://www.westnc.com/paptape.html quotes prices from $4.85 to 55 cents
per thousand feet of paper tape, and http://www.westnc.com/mylar.html
quotes prices from $17.50 to $54.00 per 500 feet of Mylar tape.

It looks like the tapes hold about 20 characters per inch (see photos
at http://www.trybusnc.com/punch.html), which would mean that 500 feet
of tape holds 120,000 bytes.  That means the cheapest (fanfold) paper
tape I looked at is around 34,000 bits per cent, while the cheapest
punched mylar tape holds around 550 bits per cent.

This is much worse than I feared.  $1 CD-Rs, by comparison, hold around
54 million bits per cent, roughly 100,000 times cheaper than punched
mylar tape.  That is to say, you could write 100,000 copies of
something on CD-Rs for the (materials) price of writing one single copy
on punched mylar tape.

The really fast tape punches punch at 150 characters per second.
Ordinary 2x CD-R drives burn at 300,000 characters per second;
expensive ones do twice that.  So writing is also 1,000 to 2,000 times
faster with CD-Rs, as well as being 100,000 times cheaper.

If your time is valued at $10 an hour, and if you do nothing but sit and
watch the tape punch or CD-R drive, then one cent of time is 3.6
seconds.  That means that 540 characters -- eight cents worth of mylar
tape -- take one cent of time to write onto mylar tape.  So the
material cost is overwhelmingly dominant.  About a million characters
-- eight million bits, or a seventh of a cent -- take one cent to write
onto CD-Rs.  So the time cost is overwhelmingly dominant.

This means the cost difference would be probably closer to four orders
of magnitude than five.

CD-R drives are very reliable; I suspect that they require less
attention than highly-mechanical paper tape punches.  Indeed, when I
write CD-Rs, I usually spend about 30 seconds paying attention per
disc; I could probably write 15 or 30 discs at once if I had the
equipment.  This suggests that the major cost in writing CD-Rs will
still be materials, not time.

So dynamic archiving on short-lived, up-to-date media is surely the way
to go.  It's much cheaper than the traditional method of spending money
on storage media (paper, disk, microfilm) up front, then letting it sit
on a dusty shelf for decades, but the cost will not all be up front.

See http://www.lesk.com/mlesk/auspres/aus.html for more.  Lesk
speculates that the cost of storing information will continue to
exponentially decrease forever, which means that the cost for storing
some piece of data in digital form for all eternity is finite and
closely comparable to the cost of storing it for a decade.  This may
not be a good assumption much further into the future.

Sorry for the disjointedness.

-- 
<kragen@pobox.com>       Kragen Sitaker     <http://www.pobox.com/~kragen/>
TurboLinux is outselling NT in Japan's retail software market 10 to 1,
so I hear. 
-- http://www.performancecomputing.com/opinions/unixriot/981218.shtml