The Basics of USB

– Alex –

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What is USB?

USB, which stands for Universal Serial Bus, has been quite successful in the computer market in the last couple of years. It started to show in PCs sometime in 1996 and started to really take off in 1998. USB is another way to connect external devices to your PC. Popular examples for USB devices are printers, scanners, keyboards, mice, joysticks, UPSs, speakers, monitors, network kits, Zip drives, digital cameras, modems, Personal Digital Assistants (PDA) and more.

Every PC comes already with at least one serial port and a parallel port to connect devices such as modems, mice, printers, etc. to your computer. The disadvantage of those two are speed as well as expandability: The serial port can only transfer one bit of data at a time, it transfers data as a series of bits, hence the name. The parallel port can only transfer 8 bits of data at a time. A PC comes only with a limited number of serial and parallel ports, therefore you’re out of luck once you used them all up. Another inconvenience of serial and parallel ports are the fact that in order to connect a device to them, you have to turn off your computer, connect the device, reboot, then manually install the driver. USB was designed to eliminate all those shortcomings.

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Speed

USB has two data transfer modes: The low speed mode transfers data at a rate of 1.5 Mbps, and is used for slow devices like keyboards, mice and joysticks. The high speed mode, used for printers, scanners, etc. can transfer data at a maximum rate of 12 Mbps, making it a lot faster than serial and parallel ports. For some applications USB might not be the best solution though. For example, you would use SCSI to connect fast drives, and Ethernet for 100Mbps networking.

Expandability

All new ATX style motherboards now come with two USB ports right on the board, I have also seen some boards that come with 4 USB ports. But with USB you can chain many devices, theoretically up to 127. You’ll probably run out of desk space and power plugs long before you max this limit out. And you can mix and match devices of all types. The downside is that most older PCs do not have a USB port, but you can add them via a PCI expansion cards.

Plug and Play

One great thing about USB is that it is fully Plug and Play compatible. Installing a USB devices is extremely easy and the closest to Plug and Play as anything has ever come. Plug in the device, install the driver, and you’re ready to go. An even nicer feature is that USB is hot-swappable, meaning you don’t even have to turn your computer off to install a new USB device. Plug it in while Windows is running. As soon as the device is connected, Windows will detect it, prompt you for the driver, install the device and make it available to you to use. With USB, there are no jumpers to set, IDs to select, or IRQ conflicts to resolve. And after installing a USB driver for a USB device once, you normally won’t have to reinstall the driver, even if you disconnect and later reconnect the device.

 

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