Messages in this thread | | | From | John Bradford <> | Subject | Re: reading from devices in RAW mode | Date | Sat, 18 Jan 2003 14:30:20 +0000 (GMT) |
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> 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 their > CRC-checks and such. Like what the CDROMREADRAW ioctl does for CD-ROMs.
CD-ROMs, floppy disks, and hard disks work in completely different ways:
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.
There is no floppy or hard disk equivillent to reading raw sectors from CD-ROMs.
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