Because the DRNG (Digital RNG) on Intel processors filter the data through a DRNG (Deterministic RNG) (i.e. NIST 800-90)[1] which is constantly reseeded.  The rdseed instruction was added later to allow for accessing the hardware generator directly (or the bits from the AES CBC-MAC conditioner directly).<p>I don&#x27;t know why rdseed was added a generation after rdrand.  Whatever the case is you can guarantee that rdrand&#x27;s internal generator gets reseeded by calling it a certain number of times[2].  You can also wait some amount of time between calls but it&#x27;s likely faster just to generate more data to force the reseed.<p>[1] Like Windows it uses AES-256 (AFAIK) in CTR mode as specified in NIST 800-90 or whatever the latest version of that standard is.<p>[2] the DRNG reseeds automatically after generating 511 128-bit samples (from Intel&#x27;s drng_samples source package)