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CompTIA A+ Certification All-in-One Exam Guide

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the CompTIA A+ 1001 exam. Just remember the names of the ports and

connectors, DB-9 and RS-232.

USB Ports

Universal serial bus (USB) connects almost every type of peripheral one

might consider today. Most folks have used USB ports and USB devices, but

let’s go beyond the user level and approach USB as techs.

Understanding USB

The core of USB is the USB host controller, an integrated circuit normally

built into the chipset. The host controller acts as the interface between the

system and every USB device that connects to it. Connected to the host

controller is a USB root hub, the part of the host controller that makes the

physical connection to the USB ports. Every USB root hub is a bus, similar in

many ways to an expansion bus. Figure 10-2 shows one possible diagram of

the relationship between the host controller, root hub, and USB ports.

Figure 10-2 Host controller, root hub, and USB ports in a typical system

A single host controller supports up to 127 USB devices, though real-life

circumstances create sharper limits. Even if a host controller supports a

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