The new Intel random number generator, code name "Bull Mountain", starts from thermal noise at 3 GHz, conditions the bits, and then uses these numbers as seeds to generate 511 pseusorandom numbers per true random number. It is this last step that I dislike and don't trust. Thermal noise has power 4kT per unit bandwidth. If you're building your own circuit, 10 MHz is a reasonable bandwidth, and at temperature 300 K, the noise is 1.6e-13 W. With a 1 MΩ input impedance, and using P = V*V/R, the RMS noise voltage is 400 μV. An amplifier gain of 2500 brings this up to a convenient 1 V, and this can be done in two or three stages using op-amps, with AC coupling between stages to avoid amplifying the op-amp bias voltages. HotBits uses a 5 μCi Cs-137 source. This is 37,000 disintegrations per second. It takes 4 consecutive pulses, at times A, B, C, D, to generate 1 bit. The time differences T1 = B - A and T2 = D - C are compared. If T1 < T2 a zero is output, if T1 > T2 a one is output, and if T1 = T2 no bit is output. After the detection efficiency and timing processing, 100 bytes per second are provided to you, but maybe also to the CIA, KGB, and Mossad. The major obstacle to a do-it-yourself implementation is that the people-who-know-what's-best-for-you make it hard to acquire radioactive materials. The cost of the 5 μCi Cs-137 source is $115, but United Nuclear, the suppler for HotBits, seems to be "sold out". -- Gene