Difference between writing file from /dev/zero and truncate

$ timeout 1 cat /dev/zero > file1 $ wc -c file1 270422016 file1 $ du file1 264084 file1 Questions : (1) How do 270422016 null characters come out to be 264084 bytes (i.e 258M). $ truncate -s 270422016 file2 $ wc -c file2 270422016 file2 $ du file2 0 file2 Questions : (2) file2 has been created with same number of null characters as file1 has, but the size of file2 is zero, why? (3) What did /dev/zero do that truncate didn't or vice versa?