Using an old PATA-to-USB cable, I attached a 15 year old PATA DVD Drive to the 
SATA based computer I've been using.  With this drive (/dev/sr1), dd seems to 
working fine without having to precede it with dvdbackup -M.

In the dvdread README on github, I found this: '..... If you attempt to read 
scrambled DVD directly with cp/dd/readom, you'll get I/O error (Read of 
scrambled sector without authentication) on all scrambled sectors ....  dvdread 
uses libdvdcss to authenticate itself to DVD drive using special IOCTLs, and 
this eliminates "Read of scrambled sector without authentication" errors'

Thomas Schmitt wrote:
> I guess that dvdbackup is aware how to talk the drive into
> descrambling. Some traces in the web point to libdvdcss
> as helper.
> Best looking, content-wise is:
> https://cromwell-intl.com/technical/how-to-copy-dvds.html

That is well done.

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