Datasheet

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Chapter 1
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Personal Computer System Components
FIGURE 1.36 D-sub ports and connectors
RJ-Series
Registered jack (RJ) connectors are most often used in telecommunications. The two most
common examples of RJ ports are RJ-11 and RJ-45. RJ-11 connectors are used most often
in telephone hookups; your home phone jack is probably an RJ-11 jack. The ports in your
external and internal modems, assuming you still have one, are RJ-11.
RJ-45 connectors, on the other hand, are most commonly found on Ethernet networks
that use twisted-pair cabling. Your Ethernet NIC likely has an RJ-45 socket on it. See
Chapter 10, “Understanding Networking,” for details on networking interfaces. Although
RJ-45 is a widely accepted description for the larger connectors, it is not correct. Generi-
cally speaking, they are 8-pin modular connectors, or 8P8C connectors, meaning there
are 8 pin positions, and all 8 of them are connected, or used. RJ-45 not only specifies the
physical appearance of the connector, but also how the contacts are wired from one end to
the other. That specification does not match the T568A and T568B wiring standards used
in data communications.
Figure 1.37 shows an RJ-11 connector on the left and an RJ-45 connector on the right.
Notice the size difference. As you can see, RJ connectors are typically square with multiple
gold contacts on the flat side. A small locking tab on the other side prevents the connector
and cable from falling or being pulled out of the jack accidentally.
Other Types of Ports
A few other ports are used with computers today. These ports include the following:
Universal Serial Bus (USB)
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IEEE 1394 (FireWire)
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Infrared
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