Electronic computers currently have many orders of magnitude more ther
modynamic degrees of freedom than information-bearing ones (bits). Bec
ause of this, these levels of description are usually considered separ
ately as hardware and software, but as devices approach fundamental ph
ysical limits these will become comparable and must be understood toge
ther. Using some simple test problems, I explore the connection betwee
n the information in a computation and the thermodynamic properties of
a system that can implement it, and outline the features of a unified
theory of the degrees of freedom in a computer.