> back in the day if you wrote to a block device with a write(2) size of anything other than a multiple of the devices actual block size you'd get a EIO or a EI

> back in the day if you wrote to a block device with a write(2) size of anything other than a multiple of the devices actual block size you'd get a EIO or a EINVAL It's not back in the day, it's still true. In Linux, block devices are kernel-cached by default, unless opened with O_DIRECT flag. In general UNIX case (for example, FreeBSD), they aren't: https://www.freebsd.org/doc/en/books/arch-handbook/driverbasics-block.html https://www.freebsd.org/doc/en/books/arch-handbook/driverbas... So, in FreeBSD "dd bs=1" will fail if it involves any disk device: disk driver will return EINVAL from read(2) or write(2) because I/O size is not divisible by physical sector size. "cat" with buffer size X (which depends on implementation) will work or not depending on divisibility of X by physical sector size, and other random factors, like short file I/O caused by delivery of the signals. Summary: dd(1) still has its place and author of original article is getting it wrong.