You are here: Home page > Computers > USB

USB memory stick with the top case removed, showing a chip inside


  • Tweet

by Chris Woodford. Last updated: December 21, 2016.

You can shake hands with someone you meet because their hand is roughly the same size and shape as yours. But just try shaking hands with a cow, a dog, or a fish. We can get along with other people because humans all broadly work the same way, think in similar ways, and talk the same language. Thankfully, the same is also now true of our computers and their peripherals (gadgets like inkjet printers, webcams, and flash memory sticks).

But that wasn't always the case. A few years ago, computers and peripherals used a mind-boggling collection of different connectors for linking to one another. It was hard (sometimes impossible) to use a certain computer with a particular printer and, if you bought a new printer, it was often touch-and-go whether it would work with your old computer. These days, virtually all computers and peripherals use a standard way of connecting together called USB. which stands for "universal serial bus." What's it all about—and how does it work?

Photo: Ever wondered what's inside a USB flash memory stick? Now you know! Notice how the USB plug (the silver square on the left—the part you insert into your computer) is soldered directly onto the circuit board by those four silver-colored lines? Solder is relatively weak stuff so those are quite fragile connections. If you insert or remove your USB stick with too much force, or push it in or pull it out at an angle, you will (sooner or later) break those links and render the thing useless. Be gentle and your stick will last for years. USB sockets on the side of your computer are very similar and may have connections that are just as fragile.

Advantages of USB

assorted serial connector plugs

Photo: Before USB: A selection of old-style serial and parallel computer connectors. They had lots of tiny copper or gold connecting pins that were easily bent or broken if you pulled or pushed them too hard.

It's universal

Twenty years ago, if you'd bought a new computer, you'd have found a whole collection of different connecting sockets or ports built into its case. There were serial ports, parallel ports, infra-red ports (for connecting things wirelessly), and all kinds of other ports. Most people had no idea what half their ports were for or what to do with them.

If you wanted to use a new peripheral, such as a webcam or printer, you had to go through a lengthy installation process. You had to install a file called a driver (which told your computer what the peripheral was and how it worked), which usually took ages. Quite often you had to reboot the computer when you were done, so installing a peripheral was incredibly slow and disruptive.

Assorted USB plugs and devices

Photo: A selection of USB adapters. Use these to convert old keyboards and mice with PS/2 plugs to work with new-style USB sockets.

In those days, the computer makers didn't really care about things working together. Acme Computers wanted you to buy their Acme printers and Acme scanners, not Bronco printers and Bronco scanners. So every manufacturer made sure its own range of products worked together but didn't really give a hoot about anyone else's. Eventually, when it became clear that users wanted to be able to use whatever peripherals they liked, the computer makers got together and agreed they'd stop being so selfish and greedy and all do things the same way. That's how USB became what's called a standard: an agreement between manufacturers to behave sensibly and cooperate.

It's "plug-and-play"

With the development of USB, everything changed. Pretty much every personal computer now has two or more USB sockets built into its case and every peripheral has a USB plug on the end of it. You can plug any USB device into any USB socket with a reasonable expectation that it will work. Even better, your computer should detect the device, figure out what it is, and try to install a driver automatically. You don't have to wait long and you don't have to reboot your computer. When you're finished using one USB device, you can just whip it out and plug in another one. Your computer will automatically detect what's going on and keep track of what's plugged into it without you having to worry in the slightest. In other words, you can "plug and play" to your heart's content.

It's much faster

USB brought another big improvement over old-style serial and parallel ports—speed— as you can see from the table below.

Connection Transfer speed In real terms Speed compared to serial


115 kbits/second.

~14500 characters, or ~2500 words per second. That's roughly twice the length of this article.


115 kbytes/second

~115,000 characters or ~20,000 words per second. That's about 17 times the length of this article.

8 times faster

USB 1.0

1.5 Mbits/second (low speed) or 12Mbits/second (full speed).

Low speed: ~187,500 characters or ~31,000 words per second. ~30 times the length of this article.

High speed: ~2.1 million characters or ~350,000 words per second. ~240 times the length of this article.

13–104 times faster.

USB 2.0

480 Mbits/second.

~60 million characters or ~10 million words per second. ~9,000 times the length of this article.

4100 times faster.

USB 3.0

5 Gbits/second.

~625 million characters or ~60 million words per second. ~54,000 times the length of this article.

40,000–50,000 times faster.


10 Gbits/second.

~1300 million characters or ~120 million words per second. ~100,000 times the length of this article.

80,000–100,000 times faster.

It also supplies power

USB has some other neat features too. The old-style serial connectors you found on computers were simply for sending data (information) back and forth. But USB also has built-in 5-volt (approximately) power leads, so it can drive most low-power peripherals without the need for an external power supply. (The two outer pins of a USB plug are the +5 volt and ground power connectors, while the two inner pins carry the data.) When you plug an external hard-drive into the USB socket of your computer, the computer is sending electric power to drive the electric motor and circuitry in the hard drive as well as sending data to and from the drive. That means you don't have to have a bulky power supply and transformer attached to the drive, so USB makes computers much more neat and compact—good news for laptop users. And the power lines have another handy benefit: you can use your computer as a charger for your laptop, cellphone, or MP3 player.

A Belkin plug-in USB PCMCIA card for a laptop

Photo: USB ports on computers are very robust, but they do break from time to time, especially after years of use. Don't worry! If you have a laptop with a PCMCIA slot, you can simply slide in a USB adapter card like this to create two brand new USB ports (or to add two more ports if you're running short).

It gives you more connections

Glance round the back of an old laptop and you'll see, perhaps, one serial port, one parallel port, and a smattering of ports for mouse, keyboard, and video: the most you can possibly connect is maybe a modem, a printer, and an external screen and keyboard. USB gives you much more connectivity. It's designed so can connect it in all kinds of flexible ways, either with one peripheral plugged into each of your USB sockets or using USB hubs (where one USB plug gives you access to a whole series of USB sockets, which can themselves have more hubs and sockets plugged into them). In theory at least, you can have 127 different USB devices attached to one computer. Quite what you'd do with all those is another matter, but you get the point.

Simply the best?

Someone plugging a USB device into a laptop usb port

Photo: USB connectors are a cinch to plug and unplug, but take a moment to ensure you've got them the right way up—and don't force them if they don't want to go in.

The greatest virtue of USB is its sheer simplicity: even your grandma can plug and unplug her webcam without studying for a PhD in computer science. The plugs are really easy to take in and out (unlike old-style parallel printer plugs, which you had to screw to the back of your computer to stop them falling out!) with hardly any force. In theory, you can't put them in the wrong way round and cause any damage. Unlike old-style connectors, they don't have lots of fragile pins to get bent up and damaged each time you take them in and out. They're very robust—so you can plug and unplug them zillions of times. There is one thing to careful about. USB sockets on computers are soldered directly to the computer's main circuit board (often quite weakly) and if you press them too hard you can break the connections, which stops them from working. So be slow and gentle when you're taking plugs in and out. Don't push them in hard or yank them back out again.

So is USB "simply the best"? In a word, "no," because it can always be better! If you own lots of gadgets and devices, you'll be astounded and bewildered by how incompatible some of them still are. Chargers are a good example: virtually every portable gadget—tablet, ebook reader, or cellphone—seems to need its own special charger with its own voltage, current, and connector. Why can't they all run off similar power levels and use a common connection like USB? One reason is that standard USB plugs and sockets are just too thick for slim modern devices. That's one reason why the USB community is urging us toward a smaller, faster, and more powerful connector called USB-C. It's still relatively new, but you can bet we'll be hearing a lot more about it in the near future.

  • Tweet
Sponsored links

Find out more

On this website



Technical documents

Please do NOT copy our articles onto blogs and other websites

Text copyright © Chris Woodford 2007, 2016. All rights reserved. Full copyright notice and terms of use.

Follow us

Rate this page

Please rate or give feedback on this page and I will make a donation to WaterAid.

Share this page

Press CTRL + D to bookmark this page for later or tell your friends about it with:

Cite this page

Woodford, Chris. (2007/2016) USB. Retrieved from [Accessed (Insert date here)]

More to explore on our website...

Back to top