คำสั่ง dd กับ cat ต่างกันอย่างไร
cat /dev/block/nandg > /sdcard/nandg.img
dd if=/dev/block/nandg of=/sdcard/nandg.img
The big difference between just plain 'cat' and 'dd' is that dd
insures that all reads and writes are done
with the size you specify. This can be significant,
depending on what device (and version of *nix) you're using
credit from
http://stackoverflow.com/questions/150697/is-dd-better-than-cat