  We have analyzed energy dissipation in a digital device (``Single-Electron
Parametron'') in which discrete degrees of freedom are used for presenting
digital information. If the switching speed is not too high, the device may
operate reversibly (adiabatically), and the energy dissipation ${\cal E}$ per
bit may be much less than the thermal energy $k_BT$. The energy-time product
${\cal E}\tau $ is, however, much larger than Planck's constant $\hbar $, at
least in the standard ``orthodox'' model of single-electron tunneling, which
was used in our calculations.
