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[filmscanners] Re: Archiving???!!!

PD drives were a precursor to the RW technology.  They both read CD-ROMS
and could read and write to PD disks.  The name came from Phase-change
Disk and was invented by Panasonic.  I still own two drives and too many
disks.  The disks held up to 650 megs, and were the same size as CD-ROMS
or other CDs, but they were held in a box cartridge.  The disks looked
like a CD, in that they had a clear side and a reflective side and were
written and read trough the clear side.

They, like CDRW, were written to and read by a laser.  The cartridge
looks identical to a CD-RAM disk (the ones that are in a cartridge, some
are made without one I believe).  There are said to have a shelf life of
at least 35 years, and can be rewritten up to 10,000 times.

What I liked most about them is that they had a permanent low level
formatting which was burned into the disk which determined all the block
locations.  As a result, the preformatting was permanent, and you could
literally change them from a Mac format to a PC format disk (when blank
or is reformatted) in something like 18 seconds.  Also, they work just
like a hard drive, or zip drive in that they store sequentially, and
material can be erased and rewritten continually without any
reformatting, but they are fully optical.

Unfortunately, one of my drives started to miswrite, and they had one
very bad habit.  Like Zip disks, they had an extra storage area so that
bad blocks could be written out and replaced with blocks from this extra
storage area, so the disk continued to have the full 650 megs when first
formatted.  However, if they began to get a lot of errors due to a bad
drive (bad laser, dirt, etc) this error area would end up filled up, and
soon the extra allocation blocks would get used up.  Once this happened,
the disk locks and can no longer be erased without a low level (or is it
high level, I always mix those up) special writer, which only Panasonic
and 3M (who made the disks) had.  So, I now have a number of these disks
that cannot be erased since no-one still has the devices to reformat
them (I asked both 3M (now Imation) and Panasonic).  Unlike CD-RW
technology, these disks cost almost $100 each in their heyday.  The last
time I picked some up on ebay they were down to $5 each.  However, the
one drive I have that works still, is a external which uses a parallel
interface, and is pretty slow (the internal was SCSI).

I would say for the most part CD-RW has taken over the need for these,
but they still had some features not found on CD-RW.  Oh well,
technology marches on...


Brad Davis wrote:
> What's "PD"?
> Brad
> On 10/12/04 2:50, "Arthur Entlich" <artistic@telus.net> wrote:
>>Sam McCandless wrote:
>>>At 4:03 AM -0800 12/9/04, Arthur Entlich wrote:
>>>>A small bit of technological information to perhaps clarify some issues.
>>>>[big snip]
>>>A nice explication, Art.
>>>Did you not deal with DVD because you agree with Brad?
>>No, I left out DVD because I haven't bought one yet, and therefore I
>>have not done a great deal of research into the units or the media.
>>Obviously, the design crams a lot more data into a smaller space, but
>>that doesn't necessarily mean the storage is less reliable.  After all
>>today's hard drives are much more reliable in terms of error rates (not
>>speaking of mechanical breakdown necessarily) than much large, older,
>>slower, and lower density units were years ago.
>>My only worry with DVD is that they hold a heck of a lot of data and a
>>failed disk could mean that much more lost.  However, as others have
>>pointed out, by triplicate copies, you get good value both in terms of
>>cost and space.  I have to admit double layering makes me nervous for
>>archiving, but 4.7 gigs isn't bad with single layer.
>>I believe the functionality of the disks in terms of DVD-+R verses
>>DVD-+RW is similar.  DVD-RAM is based upon Phase change also, in fact
>>it's precursor was PD, also invented by Panasonic, and PD disks are
>>readable on many DVD-RAM drives.
>>>>>I've been considering DVD's, but reading about the problems they many have,
>>>>>they seem to be an even more fugitive medium.

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