Re: Holo capacity

In TML subject 2186, [email removed] (Brent L. Woods) writes:

>      What's the data capacity of a holocrystal?  I've taken a
> (admittedly superficial) look through all the references I have here
> and all I could find was a note in _Traveller's Digest_ 10 that one
> holocrystal can hold about 5 hours of holographic video.  That's fine,
> as far as it goes, but it doesn't tell me how much raw data the
> crystal can hold.  If it'll hold 5 hours of video, I'd assume that the
> capacity is fairly large, but *how* large?  500 Mbytes?  1 Gbyte?  1
> Terabyte?  More?

If you're willing to accept modern film/video technology as a starting
point, throw in a dose of computer display specifications, and sprinkle
with a dash of HDTV, we can make a pretty good educated guess.  Let's
start with a little biology lesson.

Modern industrial movie cameras record at a speed of 24 fps (frames per
second), while video camcorders are more like 30 fps.  Both of these
rates, if played back to the human eye at the speed they were recorded,
would produce visible flicker.  This is eliminated in video units by
clocking playback at 60 hertz (or higher) and in movie cameras by a
rotating mirror, which rapidly flashes each individual frame 3 times,
producing a virtual playback rate of 72 fps.  playback rates of ~60
hertz and higher are beyond the humans eyes threshold to discern flicker.

Next, there's the issue of image quality.  Currently, everyday TV produces
images with a vertical resolution of ~560 lines, which shows up as a very
coarse image if frozen-framed.  Recent research in HDTV (high-definition TV)
produces video images with a vertical resolution of over 1100 lines, which
approaches the image detail in a 1280x1024 hi-res computer display.  Most
people consider this resolution satisfactory.  In fact, doubling THAT
resolution would produce images which are literally photographic quality.
Also, the number of simultaneously presentable colors affects image
quality.  Modern hi-res computer workstations (Silicon Graphics,  DEC,
Hewlett-Packard, Sun, et.al.) use 24-bit 'true' color to produce photo-
realistic images.

Given these boundary conditions (pixel depth, image dimensions, and
number of frames per second), we can estimate the amount of storage
neccessary for 5 hours of continuous visual data.  Figure 24-bit pixels
in a 1024x1024 image, scanned 60 times per second, and you end up with
1,509,949,440 bits of data per second.  Multiply that by the number of
seconds in 5 hours (18,000) and you get 2.7179 x 10^13 bits of data.
To put this into perspective, think of it as 41,180,439,290 pages of
text (66 lines, 80 columns wide), or 73,800 copies of the entire
Encyclopedia Britannica! And this is just for a silent movie, so far.
We haven't even touched on the subject of storing a parallel soundtrack.

>      Now that I think about it, this could be more generally expressed
> as, "What kind of data format is used in Traveller technology?"  Sure,
> an 8-bit byte is a _de facto_ standard today, but it doesn't necessarily
> *have* to be (at one time, it wasn't).  Also, does one "byte" correspond
> to one text character, or are all files stored in a binary form that
> includes some user-transparent data compression?  If so, do you express
> the capacity of storage media in arbitrary-number-of-bits units (i. e.,
> its physical capacity) or the amount of data that can be compressed
> onto it (its *practical* capacity).  Heck, with lharc, I can squeeze
> 1.8 Mbytes of (text) data onto one 880 Kbyte Amiga disk.  Could a TL 15
> mass storage system do any less?

These are all valid points.  Even today, it's becoming obvious that an
8-bit byte is far from sufficient for even simple text storage.  The
increasing problems of internationalization (or I14N, as people refer
to it) show that 16-bit NLS (National Language Support) is neccessary
to represent far eastern character sets such as Kanji, Katakana, Hiragana,
Triad-Chinese, etc.  Add to this the fact that most western font sets
are very generalized, or VERY specialized, and you end up with lots
of missing special characters.  For example, it's impossible for a
single 8-bit font to fully support both English and German, and still
contain all the standard punctuation characters we're all used to.

For a single font set to support all existing languages on the planet
right now, a 16-bit font would be hard pressed to serve.  24-bits would
definitely do the job.  I cite even multiples of an 8-bit byte only
for historical reasons.  There's no reason that 19, 23, or 26 bits wouldn't
work just as well.  However, since computers (at least existing ones)
are binary by their very nature, it seems that using an even power of
2 would facilitate whatever storage scheme you eventually use.  How
you choose to compress this data is left as an exercise to the reader. :-)

Regarding the compression of image data, I offer only one tantalizing
point.  Recent date compression reseach has demonstrated that very
complex natural images (a fern, a tree, a mountain skyline) can be
reduced to a single factal equation for storage, and then reproduced
in total detail, with no loss of resolution.  Optimists suggest that,
eventually, more sophisticated methods will be found which allow ANY
image to be stored in fractal form.  This form of compression results
in a storage space reduction several magnitudes of order smaller than
the original image.  The current drawback is that discerning the correct
storage fractal is very hit-and-miss, and deriving it is extremely
time-consuming.  Some images fail to be fractally compressed.

However, let's assume that eventually fractal compression becomes
common-place.  Presumably, each 1K x 1K x 24 image (discussed earlier)
could be reduced to, say, just under 1K of compressed data.  If we
further assume that compression could be done real-time, then that holo
crystal could be a lot smaller, and still hold 5 hours of data.  Now,
instead of having to hold 2.7179 x 10^13 bits of data, it only has
to hold 1,105,920,000 bits of data (138,240,000 8-bit bytes).

I don't know about you, but I always assumed that these crystals were
about half the size of a standard domino.  Considering that modern
high-density 3.5" floppy discs can already hold over 1 Mb. of data,
This only represents a 2 order of magnitude improvement in data storage
density, which doesn't seem at all unreasonable to me.

If we assume that one of these 5-hour holo-crystals is 1x2x4 cm., then
the total number of them in a cubic meter of crystal would be 100 x 50
x 25, or 125,000.  If we assume that each crystal can hold 2.7179 x
10^13 bits of data, before fractal compression, then you have 3.3974 x
10^18 bits of storage per cubic meter.  Since volume of a sphere is
stated as 4/3 pi R^3, where R (in this case) is 50,000 meters, the
total volume of a 100 Km. diameter sphere is 5.2360 x 10^14 cubic
meters.  Multiply that by the storage capacity per cubic meter, and
you have a total storage capacity of 1.7789 x 10^33 bits.

Now THAT's entertainment.

Later,

        Mark F. Cook

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        Hewlett-Packard - Interface Technology Operation
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