The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)

As mentioned in Chapter 2, USB is a fairly new technology that supports mice, keyboards, scanners, printers, and digital cameras. USB is an external serial bus that supports both low-speed and high-speed devices, and offers data transfer rates of up to 12Mbps. Some of the advantages that USB technology has to offer are listed here.

• USB can support up to 127 devices with the use of one system resource.

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• USB is plug-and-play compliant; USB devices are automatically recognized and configured by the operating system.

• USB supports hot plugging.

• The cables and connectors that are used to attach USB devices to a system are standardized.

USB devices can be ‘hot-swapped' while an operating system is up and running. This means that you can attach or detach a USB mouse or keyboard when a computer is powered on.

There are two types of USB connectors in use today. Type A USB connectors have one of their connectors permanently attached to a device, such as a keyboard or a mouse. Type B USB connectors are totally detachable from both a device and a port. Figure 8.5 displays a typical Type A USB connector.

Figure 8.5: A typical Type A USB connector.

One end of a Type A connector is actually built into the peripheral device. The other end of a Type A connector connects to a Type A port located on a host or USB hub. A Type A connector is flat and rectangular. Type B USB connectors are square and plug into a Type B USB port on both the device and the host. See Figure 8.1 for the location of USB ports on a system unit.

USB 2.0

The newest version of USB is called USB 2.0. USB 2.0 is sometimes referred to as Hi-Speed USB and supports transmission rates of up to 480Mbps. It is fully backward compatible with the early version of USB (USB 1.1). In a nutshell, USB version 2.0 uses the same exact connector cables and ports as the first version of USB. This USB specification was developed to meet the bandwidth-hungry needs of new devices and their technologies.

Here are some USB tips for the exam:

• The newest type of serial bus architecture is USB.

• A USB port can supply power for most USB devices.

• Digital devices, such as cameras, most often use USB ports.

• USB supports hot plugging of devices, such as mice and keyboards. You can connect or disconnect them when a computer system is powered up.

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• Windows 95 requires special drivers and operating system ‘supplements' before it will recognize USB devices.

• One system resource (IRQ) will support up to 127 USB devices!

The exam will ensure that you know that USB is RS232 compliant. In plain English (and on the CompTIA exam), this means that USB, RS232, and serial connections are all basically the same thing. For example, you might see something similar to this: 'What is a very popular connection method for camcorders or digital cameras?' The possible choice of answers may include USB, RS232, or serial connection. You'd better choose them all!