Re: Is ProDOS supported in OSX?

[mjmahon@aol.com (Michael J. Mahon)]

Paul Schlyter replied:

>In article <20030625041241.09942.00000955@mb-m26.aol.com>,
>Michael J. Mahon <mjmahon@aol.com> wrote:
> 
>> Paul Schlyter wrote:
>> 
>> (Hi, Paul!)
>> 
>>> Scientific data never gets obsolete, since you cannot know beforehand
>>> what data future scientists will request.
>> 
>> Exactly.
>> 
>>> BTW since scientific data more and more are recorded on digital
>>> media, this poses a long-term problem: will these media still be
>>> readable in 30 years?  In 80 years?  In 200 years?  And this isn't
>>> merely a matter about the physical medium being readable, it's
>>> also a matter about support for logical storage formats: will today's
>>> file systems be readable in 200 years?  And what about TIFF or
>>> JPEG image files?
>> 
>> I think it unlikely that we will lose the recipe for such widespread
>> data representations as JPEG.  If nothing else, such formats are
>> widely documented in books.  ;-)
> 
>Well, the format for punched cards is well-documented too.  So what
>would you do if you received a large deck of punched cards which
>contained data you wanted?
> 
>1. Try to locate some punched card reader you could use?
> 
>2. Read the specification in books and implement a new card reader
>from scratch?
> 
>3. Give up?

Paul, we were discussing data formats in the context of media
format updates.  So there will be no punched cards, only the
data from the cards stored on the latest and greatest media.
In this case, as long as the format of the data in the captured
form is known, the data can be successfully retrieved.

Again, the principle is:  continually copy old media to new
media to keep the bits fresh.

>> Of course, if some new compression technology comes along
>> that buys another factor of five or more, then someone may be
>> willing to risk de- and re-compression (generally to be avoided).
> 
>Scientific data should preferably NOT be stored in some lossy
>compression format, like JPEG ......

Agreed.  Not my example, but one of yours.  ;-)

But the ideal of lossless compression is probably not the best
tradeoff for data sent back over a data-rate-limited link from a
great distance.  There the choices are: fewer pictures with
lossless compression or several times as many pictures
with lossy compression.

If there are several overlapping frames of the same features
compressed with a lossy format, it is not too difficult to isolate
(or at least bound) the errors due to the lossy format by comparing
different frames containing the same feature.  And, of course, the
degree of "loss" in most lossy formats can be varied, so that one
frame in ten, say, is transmitted with little or no loss for reference.

If I were imaging Pluto, I would prefer, say, six pictures per unit
of transmission time with five of them using modest lossy
compression to two pictures with lossless compression.

Another, perhaps optimal, strategy would be to transmit all
frames promptly with lossy compression while retaining them
in storage, and then, after all frames were transmitted,
re-transmit them lossless as time and transmission bandwidth
permits.  One could even use the lossy frames as an "index"
to request particularly interesting frames to be sent sooner
in lossless, maximum resolution mode.

>> And if we're talking about the _really_ long term, say thousands
>> of years, then I feel safe in saying that the programs necessary
>> to decode data will be recorded as a brief preface to the data,
>> in an abstract but machine-interpretable form.  This is in many
>> ways the ultimate kind of meta-data--an operational description
>> of the data that follows.  (Or, an abstract object-oriented data
>> representation, if you will.)
> 
>If we're talking about thousands of years, we probably need to be
>concerned about the survival of our culture.  Go a few thousand years
>back and you might end up in pharaonic Egypt; their language was
>lost for many centuries, and the writings they left behind remained
>undecipherable until fairly recently.
> 
>Unspecified digital data will be even harder to decipher than
>egyptian hieroglyphs.  This includes opcodes for some abstract
>machine.

If the culture is interrupted suddenly and for a considerable
time, then this is perhaps the ultimate risk.  (If the interruption
is not sudden, then there are several extraordinary things
which could be done to improve the odds of survival of a
"bridge" to the past--multiple "mega" time capsules come
to mind, perhaps some on the surface of the Moon.)

First, we must ask how much stake we have in a future
culture, discontinuous with our own.  Perhaps they must
(and should) learn for themselves and make their own
mistakes.  ;-)

If we cannot assume cultural continuity, then the problem
of communication is much like the problem of communicating
with an extraterrestrial intelligence.  We must assume only
the minimum of shared knowledge--like mathematics, physics,
and astronomy--and then build out from there.  Data format
description is probably the least of our worries.  I would expect
that finding a way to describe what the data represents is
harder than describing how the data is represented.

>>> The older media (glass plates, used for photography) at least have
>>> one advantage: we can still examine them.  And sometimes there are
>>> demands to examine glass plates 100+ years old, for scientific
>>> purposes.
>> 
>> Indeed.  But the worlds collections of glass plates have another
>> problem, of which I'm sure you are aware--lack of space, caused
>> by lack of funds for physical preservation.
>> 
>> Increasingly, collections of glass plates are being forced to
>> relocate, with inevitable breakage, to lower-rent districts. ;-)
>> Some repositories are taking on the challenge of digitizing
>> their glass plates so that they are both more accessible to
>> researchers and less cumbersome to store.
> 
>Yes, I know about that problem too.  However, the world's collection
>of glass plates is at least not growning significantly anymore.

True.  We can hope that the existing stocks will be preserved
within the next couple of decades.

-michael

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