"String" or "Module" refers to the way the Chips are powered. Might be better to think of it as Series or Parallel. In the S1 & S3 the chips are powered in Parallel. In practice it is slightly more complex with the 12V powering a number of Buck Converters that drop the 12V to the voltage required for the Core (0.7V -1.0V) Each Buck Converter then powers a number of chips, 8 in the S1 and 2 in the S3.

In the S5 & S7 the chips power is connected in Series (Just like old style Christmas Tree Lights) So in the case of the S5 there are 15 pairs of chips in the chain, 12V /15 = 0.8V / chip. All very neat and efficient as there are no Buck Converters needed, saves money and is very efficient, But....

If one of the chips in the chain fails then at best you loose all the chips after that one and often you loose the whole chain, dependant on the failure mode.  If a chip goes open circuit (Like a bulb blowing in the Christmas Lights) as the voltages to the chips are messed.

Also worth remembering that as well as the power all of the data & control signals in all of the Miners is chained through the chips. It seems that sometimes even if a chip is not hashing it continues to pass through these signals enabling the chips further down to keep operating , however with more major failures downstream chips will stop working.


Rich