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Any amount of data. A block is described by its starting position and its size. The starting position (or beginning position) is the lowest position in the block. The end of the block is its starting position plus its size.
Group of consecutive sectors read or written in one go.
Piece of hardware containing data. Hard disc drives, cdrom drives, USB pendrives, are devices. /dev/hda, /dev/sdb, are device names (file names associated to devices).
Files are named units of data which are stored by the operating system for you to retrieve later by name. Devices and partitions are accessed by means of their associated file names.
Every part in which a device is divided. A partition normally contains a file system. /dev/hda1, /dev/sdb3, are partition names (file names associated to partitions).
As ddrescue uses standard library functions to read data from the device
being rescued, only mountable device formats can be rescued with ddrescue.
CD-ROMs and DVDs can be rescued, "compact disc digital audio" CDs can’t,
"video CDs"[1] maybe.
[1] http://en.wikipedia.org/wiki/Video_CD
Block or set of blocks to be acted upon (rescued, listed, etc). You may define it with the options --input-position, --size, and --domain-mapfile. The rescue domain defaults to the whole input file or mapfile. If ddrescue can’t determine the size of the input file, the rescue domain defaults to the maximum size of a block (at least 2^63 - 1 bytes, or 8 EiB minus 1 byte).
Ddrescue will never try to read any data outside the rescue domain except when unaligned direct disc access is requested (see Direct disc access). If it does, please, report it as a bug.
The data shown by ddrescue (amount of data rescued, number of bad areas, etc) may vary or even become zero if you limit the rescue domain. Don’t worry, they have not disappeared; they are simply out of the rescue domain specified.
Hardware block. Smallest accessible amount of data on a block device.
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