Introduction - Advanced Digital Preservation - page 2

1.1 What's So Special About Digital Things?
One might say that digital objects give rise to special concerns because the 1 s and
0 s which make up binary things are difficult to see. “ Hold on! ” you might say, “ in
the case of CD-ROMs one can, with a microscope, see the pits in the surface ”. Well
that may be true, but those little pits on the disk are not the bits.
To get to the bits one needs to unravel the various levels of bit-stuffing, the error
correction codes and logical addressing. These things are handled by the electronics
of the CD-ROM reader or of the computer hard disk, where one would be looking
at magnetic domains rather than pits, and they expose a relatively simple electronic
interface that talks to the rest of the computer systems in terms of bits. Such elec-
tronic interfaces illustrate a type of virtualisation which is widely used to allow
equipment from many manufacturers to be used in computers. However the under-
lying technology of such disks changes relatively quickly and so do the interfaces,
as a result one cannot usually use an old type of disk in a new computer. This applies
both to the well known example of floppy disks, CD-ROMs and to internal spinning
hard disks.
“ Alright ” you may say, “ I know a better, simpler way, which has been proven
to hold information for hundreds of years. How about simply writing my 1 s and
0 s on paper? Of course we could use the right acid-free paper! Or if one wanted
something for thousands of years we could take a leaf from the Ancient Egyptians
and carve the 1 s and 0 s on stone. Or to bring that up to date I know that people in
the nuclear industry are trying out writing very tiny characters on Silicon Carbide
sheets .” [ 13 ].
Those techniques would get around some problems, although one might only
want to use them for really, really, really important digital objects since they sound
as if they could be very expensive. Therefore they are not solutions for the family
photographs although they may be very good for simple text documents (although
in that case one might as well simply print the characters out rather than the 1 s and
0 s). However there are some more fundamental problems with these approaches.
For example they are not even the solution for things like spreadsheet where one
needs to know what the columns and cells mean. Similarly scientific data, as we
will see, needs a great deal of additional information in order to be usable.
1.1.1 Threats to Digital Objects of Importance to You
Take a moment to think about the digital objects which affect your life. These days
at home we have family photographs and videos, letters, emails, bank records, soft-
ware licences, identity certificates, spreadsheets of budgets and plans, encrypted
private data and also zip files containing some or all of these things. One might
have more complex things such as Word documents with linked-in spreadsheets or
databases. Widening the picture now to one's work and leisure the list might include
games, architectural plans, home finances, engineering designs, and scientific data
from many sources, models and analysis results.