USB Connectors Explained
Universal Serial Bus (USB) connectors come in a variety of types based on the intended use of the device. USB 1 devices are slower and include simple devices like mice and keyboards that don't take a large amount of bandwidth. USB 1.1 is eight times faster, and used for transfer of data more than interface devices; digital cameras and some solid state drives are good examples of this. USB 2.0 is for high speed devices including video cameras, webcams and high speed drives.
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Types
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Standard connectors always start with the 'A' type on the root or hub end of the cable, and another connection type like B, Mini-B or Micro-A on the other end. The reason for this is the cable is designed for communication from the top down, in a tiered star topology. This means that you can connect up to five layers of hubs to a single USB connection and up to 127 devices including the hubs.
Host Controllers
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There is always a host controller in the USB system where the request for data originates. USB uses a 'speak-when-spoken-to' system. meaning the device can't talk to the computer unless the computer has asked it for information first. This is one reason USB connections are designed with different ends. The request for data has to come down one way. Unlike Ethernet or phone cables, a USB cable is not wired the same on both ends.
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Device Class
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USB uses a system of device classes to make it easier for the system to know what is connected and what drivers to load. This makes it easier for developers to know what sort of driver their device should match. Different devices are different sizes, and some are small enough that the USB port would be too large to fit on them; newer phones and MP3 players are in this category. This is where the Mini-A and Mini-B connectors come into play.
Visual Identification
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The original design of the A/B cable was that the 'A' end was flatter and wider, designed for the upstream or host side, and the 'B' end was more square for the device side of the configuration. You see these often as USB printer cables today. For smaller devices, you see the Mini-A and Mini-B connections, which are both fairly flat and resemble a small version of the 'A'. Micro-A and -B are even smaller but still resemble the 'A' type.
Extensions and Limits
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Another connector is the USB extension cable. This is a cable with an 'A' connector on one end and an 'A' port on the other, so a second cable can be plugged into it. This extension can be made only up to three meters or just under 10 feet.
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References
- Photo Credit Creative Commons: http://www.flickr.com/photos/quiroso/1663465027/
