  In Part I of this series, the limits on the sustained performance of large
reversible computers were investigated and found to scale as $\sqrt{AV}$ where
$A$ is the convex bounding surface area of the system and $V$ its internal
volume, compared to $A$ for an irreversible computer. This analysis neglected
to consider interactions between components of the system however, instead
focussing on raw computational power. In this part we extend this analysis to
consider synchronisation events such as communication between independent
reversible processors subject to a limiting supply of free energy. It is found
that, whilst asynchronous computation can proceed at a rate $b\lambda$,
synchronisation events proceed at the much slower rate $\sim b^2\lambda$; in
these rate expressions, $\lambda$ is the gross transition rate for each
processor and $b\sim\sqrt{A/V}\ll1$ is the 'computational bias' measuring the
net fraction of transitions which are successful. Whilst derived for Brownian
reversible computers, this result applies to all forms of reversible computer,
including Quantum computers. In fact this result is an upper bound, and one
must choose the phase space geometry of the synchronisation events carefully to
avoid even worse performance. In the limit of large computers, communication
will therefore tend to freeze out as $b\to0$; if, however, one is willing to
restrict the number of processors permitted to share state at any given time
then this rate can be ameliorated and performance on par with asynchronous
computation can be recovered.
