Date: Tue, 25 Nov 2003 00:57:38 +0100 From: Stefan =?iso-8859-1?Q?E=DFer?= <se@FreeBSD.org> To: Dag-Erling =?iso-8859-1?Q?Sm=F8rgrav?= <des@des.no> Cc: freebsd-hackers@freebsd.org Subject: Re: "secure" file flag? Message-ID: <20031124235738.GA4107@StefanEsser.FreeBSD.org> In-Reply-To: <xzpn0amqahi.fsf@dwp.des.no> References: <20031119003133.18473.qmail@web11404.mail.yahoo.com> <200311230019.11310.wes@softweyr.com> <20031123124620.GB1133@StefanEsser.FreeBSD.org> <200311231011.32965.wes@softweyr.com> <20031124102940.GC1168@StefanEsser.FreeBSD.org> <xzpn0amqahi.fsf@dwp.des.no>
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On 2003-11-24 12:20 +0100, Dag-Erling Sm=F8rgrav <des@des.no> wrote: > Stefan E=DFer <se@FreeBSD.org> writes: > > Ok. I've also thought some about this, and I think that different med= ia > > might need different methods (i.e. MFM vs. RLL vs. PRML, but also vs.= =20 > > Flash media). >=20 > 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=20 to mean 1,7 RLL offering a 2/3 coding, while PRML starts at 8/9=20 and current devices use up to 24/25 (i.e. 24 bits in 25 channel bits).=20 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=20 an RLL encoded data stream. What matters is what can be read back=20 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=20 encoding can be decoded with similar effort ... And that is what this thread is about: Secure removal of data from=20 storage media. There definitely is a difference between RLL (as in=20 1,7i RLL) and modern PRML drives under this aspect. Regards, STefan
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