Messages in this thread | | | From | "Folkert van Heusden" <> | Subject | RE: reading from devices in RAW mode | Date | 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 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.
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).
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |