[Ham-Computers] DBD Terms, The Differences?

[Jay Eimer]

Commercially manufactured DVDs (and CDs) use a metal disk that has "pits"
pressed into it to encode the data.  Then they're covered with a clear
plastic protective surface.  The pits don't reflect the laser like the
smooth surface where there are no pits.  In effect, they're pressed like an
vinyl LP.  Writable DVD-R (and CD-R) media use a dye that is clear until
heated, and then turns opaque once they're hit with a strongish laser,
likewise destroying the reflectivity.  Where they're not burned, they still
reflect.  The "read" laser is lower powered and doesn't induce the phase
(color) shift in the dye while reading.

This is why CD-R and DVD-R disks can go bad over time.  The dye breaks down,
and exposure to heat can cause the dye to phase shift randomly.  Neither
happens with a pressed disk.

But the cost of setting up a master and pressing a disk is significant.
Small runs are almost always burned, rather than pressed.

Jay

-----Original Message-----
From: ham-computers-bounces at mailman.qth.net
[mailto:ham-computers-bounces at mailman.qth.net] On Behalf Of Duane Fischer,
W8DBF
Sent: Thursday, June 23, 2005 11:59
To: ham-computers at mailman.qth.net
Subject: [Ham-Computers] DBD Terms, The Differences?



	
Hello All, 	
	
Can one of you explain to me what the exact difference between a
"manufactured DVD" and a "duplicated -R DVD" is? The duplicated is used for
low quanity and the manufactured, which uses a completely different format
and equipment, for
higher quanities, such as more than a thousand. production	
	
I am wondering why the low quanity production is four times as much money to
have done and why two different formats are needed? 	
	
Thank you.	
	
Duane Fischer, W8DBF	
dfischer at usol.com	

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