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Figure 3-6 Typical desktop computer with peripherals

External Connections

Every peripheral connects to the system unit through one of the many types of ports. The back of a typical system unit (Figure 3-7) has many cables running from the system unit to the various peripherals. You may even have a few connectors in the front. All of these connectors and ports have their own naming conventions, and a good tech knows all of them. It’s not acceptable to go around saying such things as “That’s a printer port” or “That’s a little-type keyboard connector.” You need to be comfortable with the more commonly used naming conventions so you can say “That’s a female DB-25” or “That’s a USB connector.”

Figure 3-7 Connections in the back of a PC

Plugs, Ports, Jacks, and Connectors

Although PCs use close to 50 different types of connections, almost all fit into one of six major types: DIN, USB, FireWire, DB, RJ, and audio. Read the next paragraph to get your terminology straight and then you can jump into the various connectors with gusto.

No one seems to use the terms plug, port, jack, or connector correctly, so let’s get this right from the start. To connect one device to another, you need a cable containing the wires that make the connection. On each device, as well as on each end of the connecting cable, you need standardized parts to make that connection. Because these are usually electrical connections, one part needs to fit inside another to make a snug, safe connection.

A plug is a part with some type of projection that goes into a port. A port is a part that has some type of matching hole or slot that accepts the plug. You never put a port into a plug; it’s always the other way around. The term jack is used as an alternative to port, so you may also put a plug into a jack. The term connector describes either a port or a plug. As you progress though this chapter and see the various plugs and ports, this will become clearer (Figure 3-8).

Figure 3-8 Plug, port, and jack

Mini-DIN Connectors

Most PCs sport the European-designed mini-DIN connectors. The original DIN connector was replaced by mini-DIN a long time ago, so you’ll only see mini-DIN connectors on your PC (see Figure 3-9 bottom). Older-style keyboards and mice plugged into DIN ports (Figure 3-9 top).

USB Connectors

Universal serial bus (USB) provides the most common general-purpose connection for PCs. You’ll find USB versions of many devices, such as mice, keyboards, scanners, cameras, and printers. USB connections come in three sizes: A, B, and mini-B. The USB A connector’s distinctive rectangular shape makes it easily recognizable (Figure 3-10).

Figure 3-9 DIN (top) and mini-DIN (bottom) connectors

Figure 3-10 USB A connector and port

You never see a USB B connector on your computer. USB B connecters are for the other end of the USB cable, where it attaches to the USB device (Figure 3-11).

Figure 3-11 USB B connector

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NOTE You’ll sometimes hear USB ports and plugs described as upstream or downstream, terms that create rather amusing conversation and confusion. It’s all about whether you refer to the plug or the port, so here’s the scoop. The USB A plugs go upstream to USB A ports on the host or hub. USB A ports provide downstream output from the host or hub. So the plug is upstream and the port is downstream.

Just to add more fun to the mix, USB B plugs go downstream to devices. USB B ports provide upstream output from the device to the host or hub. My advice? Stick with A or B and nobody will get confused.

The USB B connector’s relatively large size makes it less than optimal for small devices such as cameras, so the USB folks also make the smaller mini-B–style connector shown in Figure 3-12.

Figure 3-12 USB mini-B connector

USB has a number of features that make it particularly popular on PCs. First, USB devices are hot-swappable, which means you can insert or remove them without restarting your PC. Almost every other type of connector requires you to