RE: reading from devices in RAW mode
Folkert van Heusden (email@example.com)
Sat, 18 Jan 2003 17:03:39 +0100
> > Is it such a newby question? Your suggestion of using dd is totally NOT
> > what I meant: I want to read from devices with the devices ignoring
> > CRC-checks and such. Like what the CDROMREADRAW ioctl does for CD-ROMs.
> CD-ROMs, floppy disks, and hard disks work in completely different
> All modern forms of storage use powerful error correction below the
> sector level. Floppies are the exception here, they typically use MFM
> encoding, which is relatively straightforward.
> Audio Compact discs use powerful error correction anyway, but CD-ROMs
> use some of the capacity which was previously used for audio data for
> a second level of error correction, so there are two sector sizes,
> (RAW, and COOKED). Reading RAW sectors, does not come close to
> allowing you to read individual pits and flats on the disc, it just
> lets you bypass the top level of error correction. The data is still
> being error corrected by lower layers.
oh, ok. But I will still get more data back then with reading through
the regular, say, /dev/hdc-device wouldn't I? As far as I know, read
will only give you data when no I/O error occured.
> There is no floppy or hard disk equivillent to reading raw sectors
> from CD-ROMs.
Really? Are you really sure about that?
Back in the old days, when I did assembly on my Atari ST, I would just
say to the controller "gimme this and that track, in RAW" and it
would do so. I thought that I could do that at least for floppy, not
sure about harddisk (RLL through ACSI interface).
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