<b_jonas> slashlearn =@ccc/=@ccc is a great innovation in gcc 6, kept top secret, where inline asm statements can return a value in the carry flag on x86_64. See https://gcc.gnu.org/gcc-6/changes.html which keeps this secret, https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/Extended-Asm.html , http://article.gmane.org/gmane.linux.kernel/2238065 .

Block devices are a concession made in Unix to make raw hard disks and magnetic tape have a similar interface to regular files and terminals. Since magnetic tapes can't write individual bytes, only entire blocks, the interface isn't exactly the same, thus the dreaded dd obs= option was born.