"secure" file flag?
se at FreeBSD.org
Mon Nov 24 15:57:44 PST 2003
On 2003-11-24 12:20 +0100, Dag-Erling Smørgrav <des at des.no> wrote:
> Stefan Eßer <se at FreeBSD.org> writes:
> > Ok. I've also thought some about this, and I think that different media
> > might need different methods (i.e. MFM vs. RLL vs. PRML, but also vs.
> > Flash media).
> PRML is not an encoding scheme like MFM or RLL, it is an algorithm for
> recovering a bitstream from a weak analog signal. Modern disks mostly
> use RLL encoding.
So what? PRML is not complementary to RLL. RLL is typically used
to mean 1,7 RLL offering a 2/3 coding, while PRML starts at 8/9
and current devices use up to 24/25 (i.e. 24 bits in 25 channel bits).
MFM can be considered a special case of RLL encoding, too, BTW ...
But it's utterly irrelevant, that PRML data is written to disk as
an RLL encoded data stream. What matters is what can be read back
from the disk media (and PRML is about reading, not writing ;-)
You probably don't want to claim that 1,7 RLL and a modern PRML
encoding can be decoded with similar effort ...
And that is what this thread is about: Secure removal of data from
storage media. There definitely is a difference between RLL (as in
1,7i RLL) and modern PRML drives under this aspect.
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