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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0111:  Peripheral Devices
      9  III  Peripheral Device Interfaces

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USB

The Universal Serial Bus, or USB, is a peripheral interface that is rapidly replacing serial and parallel communications. USB was developed by a group of industry giants such as Compaq, IBM, Intel, Microsoft, NEC and Nortel Networks. Originally intended as an interface for low bandwidth devices such as modems, keyboards, mice, and printers, many hardware manufacturers now use the USB interface for other devices such as CD-RWs and external hard drives.

The most exciting thing about USB is that it's truly "plug and play." The USB interface allows you to plug in and unplug devices while the computer is running. This is known as "hot swapping" or "hot plugging." When devices are plugged into the interface, the operating system will prompt the user for the proper device drivers. After the drivers are loaded and configured, the user can unplug the device and plug it in again any time without reinstalling the drivers.

The current specification found on nearly all new PCs is USB 1.1. It allows for 127 devices to be attached to one USB interface, with an overall bandwidth of 12 Mb per second that is shared by all the devices in the chain. The interface that is built onto the motherboard or USB controller card is referred to as a root hub. Most new motherboards come with two integrated USB root hubs. Devices can be attached directly to the root hub, or you can attach a USB hub with multiple USB ports to the root hub. The specification also puts a 10m limit on the length of any USB chain.

USB 2.0

The new USB 2.0 specification hit the market in the 2nd quarter of 2001. This new specification increases the bandwidth from 12 Mb per second to 480 Mb per second. USB 2.0 (HS-USB) devices are backwards compatible with USB 1.1 devices.

What is truly exciting about this new specification is that its high-speed bandwidth is greater than current IDE standards. Theoretically, we could see an external hard drive with greater throughput than an internal hard drive with hot swapping capabilities. HS-USB is found on the newest system boards, and PCI adapters are available for older systems. The new logo is shown in
Figure 82.



Figure 82: USB 2.0 logo (Courtesy of USB.org)

 


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