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CompTIA A+ Certification All-in-One Exam Guide

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bulbs or switches on the CPU. You can, however, see little wires sticking out

of many CPUs (see Figure 3-4). If you apply voltage to one of these wires,

you in essence flip the switch. Get the idea? So, if that wire had voltage and

if a tiny light bulb were attached to the wire, that light bulb would glow,

would it not? By the same token, if the wire had no power, the light bulb

would not glow. That is why the switch-and-light-bulb analogy may help you

picture these little wires constantly flashing on and off.

Figure 3-4 Close-up of the underside of a CPU

Now that the EDB enables you to communicate with the Man in the Box,

you need to see how it works by placing voltages on the wires. This brings up

a naming problem. It’s a hassle to say something like “on-off-on-off-on-onoff-off”

when talking about which wires have voltage. Rather than saying

that one of the EDB wires is on or off, use the number 1 to represent on and

the number 0 to represent off (see Figure 3-5). That way, instead of

describing the state of the lights as “on-off-on-off-on-on-off-off,” I can

instead describe them by writing “10101100.”

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