  We consider the first laws of thermodynamics for a pair of systems made up of
the two horizons of a Kerr-Newman black hole. These two systems are constructed
in such a way that we only demand their ``horizon areas'' to be the sum and
difference of that of the outer and inner horizons of their prototype.
Remarkably, these two copies bear a striking resemblance to the right- and
left-movers in string theory and D-brane physics. Our reformulation of the
first law of black hole thermodynamics can be thought of as an analogy of
thermodynamics of effective string or D-brane models.
