Re: [ARSCLIST] Hard disk drives and DAT

[Don Cox <doncox@xxxxxxxxxxxxxx>]

On 31/03/07, Jerry Hartke wrote:


> Such a proposal is not practical. In order to read optical media in
> any practical environment, the microscopic data features must have a
> transparent cover layer. The thickness of this layer is 1.2 mm for CD,
> 0.6 mm for DVD and HD DVD, and 0.1 mm for BD. The cover layer creates
> an entrance surface that is remote from the information layer. The
> laser beam is out-of-focus at the entrance surface, thereby minimizing
> beam degradation from dust, fingerprints, and scratches.

We all know that. 

Pits would be etched (by laser) on the archival surface, which would then be
protected by a layer of glass or possibly polycarbonate. 

Alternately, dust and marks could be removed from the surface before
reading. There would be no scratches unless the user wore diamond rings.

There is no particular reason why archival disks should match the
dimensions of standard disks, although it would be convenient.

Regards
-- 
Don Cox
doncox@xxxxxxxxxxxxxx