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What is called "USB"?

Olga Weis Olga Weis Last updated Aug 27, 2021

USB, short for Universal Serial Bus, is a widely used is a cable system that includes physical cables, connectors and communication protocols. Nowadays most of the peripherals and devices use USB cables to connect to computers – cameras, printers, scanners, external drives, etc. All major operating systems support USB technology.

In the article below I’ll tell you what USB is, describe different types of USB connectors, compare classic USB 2.0 with new USB 3.0 and show you the difference between popular Mini and Micro USB. Let’s get started!

  1. What is USB
  2. Types of USB connectors
  3. Most popular USB devices
  4. USB 2.0 vs. USB 3.0
  5. Mini vs. Micro

What is USB

As we mentioned above, USB stands for Universal Serial Bus. This standard of cable system was developed in mid-90s, when seven technology companies – Microsoft, Compaq, Intel, IBM, Nortel, DEC and NEC – joined their efforts to create a cable system that would make it easier to connect various devices and peripherals to computers. The first USB – USB 1.0 – was capable of transferring data at the rate of 12 Mbps and supporting 127 devices. What we mostly use these days is USB 2.0; it transfers data at 480 Mbps and supports USB 1.0 and 1.1 devices and cables. The development of the technology means improvement of the speed and performance, there is special forum that supports USB technology’s advancement and adaption known as USB Implementers Forum (USB-iF).


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Types of USB connectors

When the technology just came into existence, only two connector types were detailed in the original specification – standard A and standard B. Now there are many more types of connectors, but the majority of devices and peripherals still do with A-connector and B-connector interfaces.

USB A-Type

The A-type connector has a flattened rectangular interface. It uses flat contacts instead of round pins and holds connection by friction, thus allowing users to connect and disconnect to a device / peripheral easily. The A-type connectors are mostly used on host controllers and hubs.

This type of connectors are plugged into a downstream port, i.e. a port that connects to a host device (PC), as opposed to upstream ports where you plug in peripheral devices.The host - be it a controller or hub - provides 5V DC power on a USB pin. You cannot use a cable where both ends are A connectors to connect two hosts. This may damage computers, you will need to check with manufacturer before transferring data over an A-A cable.

A-A cables can also be used for connecting USB devices with an A-style female port to a PC or another USB device.

USB B-Type

The B-style connector has a square shape with slightly slanting corners. It also uses friction to hold connection in place. It is usually plugged into an “upstream receptacle” used on peripheral devices. Most of USB applications use a two-connector-type scheme, i.e. A-B cable.

USB C-Type

This is the latest addition to the family of USB connectors. A reversible-plug connector, it can be plugged into any USB-C device using either end.

It connects to both hosts and devices; commonly used for pairing with almost all types of USB-connectors, including USB-A, USB-B, USB Micro-B. It is compatible with the following versions of USB technology - USB 1.1, USB 2.0, USB 3.0, USB 3.1 and can be adapted to interact with all legacy connectors.

Two USB 3.1 devices connected by a USB C-type cable can exchange data at the speed of 10 Gbps and send upto 100 Watts power to a device. USB C cables support DisplayPort video to send HD video and audio from a source device to a display, and four-channel audio system (left front, left back, right front, right back audio signas).

Most popular USB devices

The number of devices and peripherals that can be connected to your computer via USB cable keeps increasing – there must be millions of them by now. Here we list the most popular ones.


There is hardly any need to describe what a camera is. Perhaps it would be enough to say that ever since digital cameras have replaced film cameras, we use USB cables to transfer pictures and videos from a camera to a PC. There are different cables for transferring high-definition videos and pictures.

External drive

It is also called “an external storage device”, i.e. a device for storing data externally. A floppy disk and tape drive are the earliest examples of it.The earliest storage devices were a floppy disk, tape drive, etc. Most of modern external hard drives are attached to a computer through a USB connection.


Yes, this popular device by Apple also connects to a computer via USB port – fill it in with songs and videos, the device can store up to 10 000 songs.

Keyboard & Mouse

Sure, there are wireless keyboards and mice nowadays, but if you type a lot and type fast USB keyboard is what you should look for. Wireless keyboards at times do not react to keystrokes or take some time to react. Also, your old good USB input devices do not need configuration; you can use them immediately after plugging in.


Apart from recording vocals and instruments, a USB mic is of great help when you are podcasting or giving an interview over Skype. It is a great alternative to high-end studio hardware.


This is easily the most used computing peripheral device often defined as ‘a device that prints texts or illustrations on paper’, although nowadays you can print not only text and illustrations and not only on paper. There are many types of printers and there are many ways a printer can connect to a computer, the most common being a USB port.


Initially the term was used for the control column of an aircraft. We are talking about a device that helps you control movement of an image on a computer or any other display screen, with push buttons aka switches, etc. And guess what? We usually use USB cables to connect a joystick to a computer.


A device used for optically scanning texts, documents or other objects and converting them into digital data. The most commonly used interface for transferring scans from a device to a computer is a USB interface.


A mobile phone that apart from phone’s functionality offers features of other devices such as a camera, media player, etc. It typically uses a USB interface to physically connect to a computer, also there is USB OTG (On The Go) that enables devices to talk to each other without a mediating PC.


A portable computer with a touchscreen interface that you can use for viewing presentations, having video-conferences, watching movies, sharing photos, etc. It connects directly to your computer with the help of a USB cable.


A digital camera connected to your computer that enables you to send live pictures over Internet. Some webcams are wireless, while others are plugged into computers through USB ports.

USB 2.0 vs USB 3.0

Released in April 2000 November 2008
Signaling RateHigh Speed (HS) 480 MbpsSuper Speed (SS) at 4.8 Gbps, 10 times faster than USB 2.0
Signaling MethodEither sends or receives data (half duplex), so-called polling mechanismSends and receives data simultaneously (full duplex), so-called asynchronous mechanism
PriceFor a similar product the USB 2.0 version is generally less expensive than the USB 3.0 versionMore expensive as compared to USB 2.0
Power UsageUp to 500 mAUp to 900 mA. Consumes less power when in idle state, powers more devices from one hub, i.e. offers better power efficiency.
Number of wires within the cable49
A-type connectorsGrey in colorBlue in color
B-type connectorsSmaller in sizeExtra space for more wires
Max Cable length5 meters3 meters

Mini USB vs. Micro USB

In addition to A-type and B-type USB connectors are categorized into micro and mini. It is possible for a single USB cable to have both connectors. A micro or mini USB cable would have two ends – male and female. The former is the end of a USB cable inserted in MP3 players, cameras and other peripheral devices, the latter is what you see on your computer.

Mini USB

Mini USB, as its name suggests, is smaller than standard USB. You can see it at the end of charger or data cable connected to your camera or mobile phone. Have a look at it and you will see it has five pins, while a standard USB has four of them. The fifth pin is known as ID pin and it is required for upgrading mini USB properties in the future. Mini USB typically either send or receive data, i.e. they work in a single direction. They are also used a charger connector.

A normal life cycle is 5 000 connect/disconnect cycles, then the functionality starts deteriorating.

Micro USB

Micro USB is even thinner than mini USB, it could be a data cable, charger or connector for digital cameras and mobile devices. Compared to mini USB, it has a longer life cycle – up to 10 000 connect/disconnects. They are adopted for female USB ports of cameras and mobiles, have five pins and all of them are in operative mode. That is why micro USB cables can work in smartphones and tablets. The data can travel both ways at the same time.

Mini USB compared to micro USB

Here is the list of major differences between the two:

  • Both mini USB and micro USB have five pins. However the fifth pin in mini USB is not operative, while it works in micro USB AB cable.
  • Micro USB lasts longer – 10 000 connect/ disconnect cycles compared to 5 000 of mini USB.
  • Mini USB are usually meant for a single purpose – either for storing data or connecting power. Micro USBs – thanks to the operative fifth pin – can work as the standard connector both for data and power.
  • Mini USB can be used for a larger number of devices compared to micro USB – laptops, computers, mobile phones, cameras, etc. Micro USBs area of use is mainly smartphones and digital cameras.
  • Micro USB is to replace all other USB types pretty soon. Major mobile phone manufacturers are said to have signed an agreement to uniformly use micro USB ports for charging and data transfer.