How to quickly check RAM on Linux

How does the given command check RAM?

  dd if=/dev/zero of=/run/zero.bin bs=1G count=8
  sha1sum /run/zero.bin

/dev/zero is a special file that always returns zeros. Nothing in there looks like it touches more than a trivial amount of RAM.

Plus, this test can't tell if a bit is always zero.

Also look at memtester[0] as a userspace tool.

[0] http://pyropus.ca/software/memtester/