You are correct; and of course, any hardware-level behaviour is likely to be implementation defined. I should note that MSVC [1] guarantees "non-deterministic a

You are correct; and of course, any hardware-level behaviour is likely to be implementation defined. I should note that MSVC [1] guarantees "non-deterministic and cryptographically secure" behaviour; and that libc++ [2] uses the "cryptographically secure" rand_s [3] on Windows, NaCl on other platforms where NaCl is available, and /dev/urandom where it isn't. [1] http://msdn.microsoft.com/en-us/library/bb982250.aspx http://msdn.microsoft.com/en-us/library/bb982250.aspx [2] https://github.com/llvm-mirror/libcxx/blob/master/src/random.cpp https://github.com/llvm-mirror/libcxx/blob/master/src/random... [3] http://msdn.microsoft.com/en-us/library/sxtz2fa8.aspx http://msdn.microsoft.com/en-us/library/sxtz2fa8.aspx