Hacking the Xbox

Chapter 2 - Thinking Inside the Box 35
Components are classified as passive and active. Loosely speaking,
passive components cannot amplify a signal, so they usually have just two
leads. Sometimes multiple passive components are packaged together, so
a single package of passive components will have multiple leads. Passive
components include capacitors, resistors and inductors. The most
common passive components on the Xbox motherboard are capacitors.
Capacitors store energy as an electric charge; in the Xbox, they are
Figure 2-2: Typical passive components in an Xbox.
Why Do Circuit Board Traces
Meander Everywhere?
After looking at a few circuit boards, you will probably start
noticing that the traces on the circuit board often times
meander all over the place, sometimes going back and
forth several times before connecting to their destination.
This seems pointless when a straight trace would do the
trick. However, rarely will you find a structure on a circuit
board that was placed as a flighty whim by the designer. It
turns out that the speed of signals in most high- end electronic
devices, about ¼ the speed of light, is slow compared
to the time required for a signal to arrive at its destination.
For example, a signal will only travel 3 inches on a
circuit board during one clock cycle in a 1 GHz processor
(one clock tick at 1 GHz is a duration of 1 billionth of a
second, or one nanosecond). Thus, two signals starting from
the same chip will arrive at their destination at quite different
times if the trace lengths are very different. To combat
this, designers will put extra bends into the shorter trace so
that the effective length of the trace is the same as the
longer one.