What is USB? [Android A to Z]

What is USB?  USB stands for Universal Serial Bus, and is a standard for connectors, cables and protocols used for data transfer and power between a computer and another electronic device.  It was developed in 1995 to allow a single connection method for things like computer keyboards, mice, and printers as well as connected devices like mp3 players and cameras. A standard USB interface has four wires (USB 3.0 has eight for double the data transfer), with two acting as power leads and two for data transfer. Commercial applications have up to eight wires and connection points, and can also provide 12- or 24-volt power in addition to the normal 5 volts. You'll see these sort of systems in cash registers and commercial barcode scanners.  

What we're most interested in is the implementation in mobile devices.  Most mobile devices in the world use USB 2.0 for data transfer and/or power supply. In China, laws have been passed making manufacturers keep to the USB standard for data transfer and power, and in December 2011 a law was written that all mobile phones will be able to use the same charger, with micro-USB as the standard, by the European Committee for Electrotechnical Standardisation. This only affects phones -- tablets and laptops are exempt because they have different power requirements.

Most new Android phones you'll buy have a microUSB (like the picture above) connector. The data cable will have a small plug to insert into the phone on one end, and a standard USB connector to plug into your computer. This cable will allow for data transfer -- to copy pictures or music or do a little hacking, as well as 5 volts to charge the device.  Some older models have a miniUSB connector, which does the same thing but with a different, slightly larger, port. MicroUSB is a more robust connector, being rated at 10,000 "insertion cycles" so both the port on the phone as well as the cable should last longer. Some devices need a non-standard USB connector, like the Galaxy Tab 10.1 (or nearly every other Android tablet). Internal design doesn't permit a standard microUSB connector to fit on the board, so a wider, thinner plug and port combo was used.  Also, some tablets can't get power fast enough to charge via a USB connector and use a separate DC socket and adapter for charging. For devices like the iPhone that have a non-standard connection port, an adapter can be made to allow them to comply with European mandates of a single charger solution.  

Lastly, some phones use the microUSB interface for other things besides data transfer and power.  Seeing HDMI output provided through a MHL (Mobile High-definition Link) is becoming pretty common, and allows a special adapter to be used to provide high definition video to stream out to televisions or computer monitors. These adapters can be purchased for about 15 dollars (US) and allow a standard HDMI cable to connect to your phone.  

We've seen other connection methods come and go, and new ones are always being worked on, but USB offers relatively high-speed data transfer, is adaptable for various power needs, and is likely to stick around for a long time.

Previously on Android A to Z: What is tethering?; Find more in the Android Dictionary

More from the Android Dictionary


Jerry Hildenbrand
Senior Editor — Google Ecosystem

Jerry is an amateur woodworker and struggling shade tree mechanic. There's nothing he can't take apart, but many things he can't reassemble. You'll find him writing and speaking his loud opinion on Android Central and occasionally on Twitter.

  • Jerry the last part of the first paragraph is unclear when you start talking about voltage of 12 to 24. You should make it clear these are NOT STANDARD USB connectors. Nothing but 5 volts is supported by any of the USB standards, and you can't call it a USB port if it does not ad-hear to the standards. The standard says: The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 3.0, the voltage supplied by low-powered hub ports is 4.45–5.25 V. Powered USB is a whole different standard, which is not necessarily safe to plug your phone into because some early versions has the wrong voltage in the wrong pins.
  • that moving part USB door in the photo makes me cringe. bad design!
  • Didn't Wilt Chamberlain have over "10,000 insertion cycles" too? Though i doubt he's packing a micro-usb Sorry. Couldn't help it.
  • Why should Apple be able to get a pass with an adapter? A standard should be a standard. There are already adapters.
  • Hmmm they could just add Apple port to micro-USB adapter, they use there plug but still uses USB standard to communicate. More problem would be if they EU regulation prevent that too and Apple can't just throw there port like that since it do more stuff then just USB. maybe extra port but that would be kind of odd.
  • Exactly. I suspect money changed hands. The idea was you could forget your cord at home and it was no big deal because 5 bucks buys you a new charger and cord, and hotels could even have them at the desk. Everybody toes the line except Apple.
  • You should have emphasized the seismic change that USB represented, namely that it was plug'n play. Before that, many devices required you to shut down the computer before connecting them.
  • Looking forward to subvert the age of products were developed
  • It is really interesting and I am sure that other people thinks this too.