Besides size and energy (temperature), another important yardstick
exists for measuring the universe, complexity. Complexity
is accompanied by organization between components, by structure,
orderliness, and low entropy. As we construct more and more intricate
machines, we find that certain capabilities are a function of the
level of complexity of the machine, more than of the particular
components from which it is constructed. One can build a clock,
or an elementary calculating machine, out of wood, metal, or plastic.
The capabilities of the calculator are limited not so much by the
materials themselves as by their organization. Such a simple machine
cannot alter its preset operations, or make choices based on the
state of the machine at any given moment. From more elaborate hardware
one can build a digital computer. This machine now can do everything
that the primitive calculating machine can do, and much more. It
can accept and emit data, can recall, and can calculate in ways
not only not preprogrammed in the hardware, but not even anticipated
by the builders. It can make choices or decisions for future
actions based on the current state of its information, and can "learn"
to make better decisions from the outcome of previous trials.
very same computer in a functional sense can be built from quite
different raw materials. It can use vacuum tubes or transistors.
Its physical memory storage may involve solenoid switches, mercury
delay lines, cathode-ray tubes, or magnetic tapes, drums, or core.