  The holographic principle has revealed that physical systems in 3-D space,
black holes included, are basically two-dimensional as far as their information
content is concerned. This conclusion is complemented by one sketched here: as
far as entropy or information flow is concerned, a black hole behaves as a
one-dimensional channel. We define a channel in flat spacetime in thermodynamic
terms, and contrast it with common entropy emitting systems. A black hole is
more like the former: its entropy output is related to the emitted power as it
would be for a one-dimensional channel, and disposal of an information stream
down a black hole is limited by the power invested in the same way as for a
one-dimensional channel.
