introduction

4.1. Definition of USB
A Universal Serial Bus (USB) is a common interface that enables communication between devices and a host controller such as a personal computer (PC).
It connects peripheral devices such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives and flash drives.
Because of its wide variety of uses, including support for electrical power, the USB has replaced a wide range of interfaces like the parallel and serial port.

4.2. USB Identification
Although there are several types of USB connectors, the majority of USB cables are one of two types, type A and type B. The USB 2.0 standard is type A; it has a flat rectangle interface that inserts into a hub or USB host which transmits data and supplies power. A keyboard or mouse are common examples of a type A USB connector. A type B USB connector is square with slanted exterior corners. It is connected to an upstream port that uses a removable cable such as a printer. The type B connector also transmits data and supplies power.
There is also USB3, the main difference between the standards is speed. The maximum bandwidth of 3.0 is over 10 times higher than 2.0. This doesn’t mean transfer speeds are ten times better in the real world, but there is a huge difference. You’ll see much quicker file transfers with a USB 3.0 drive plugged in to a 3.0 port. Transfer speeds are not better if you plug a 3.0 drive into a 2.0 port. Data can still be transferred, but only at 2.0 speeds.