Difference between USB 2.0 and USB 3.0
Universal Serial Bus (USB) ports and plugs are tools that allow you to connect computer peripherals to your computers, keyboards, external hard drives, or storage keys.
The numbers following the USB symbol simply correspond to the version of the USB standard in question, with the 3.0 and 3.1 series being the most recent at the time these lines are written.
In addition to the color of their connectors (version 3.0 is usually blue), the data transfer speed is the main difference between these two standards.
Thus, the USB 2.0 standard, introduced in 2000, made it possible to guarantee a transfer speed much higher than the previous standard: from 1.5 MB per second to the theoretical 60 MB! USB 3.0, released in 2008, has multiplied this transfer rate by 10, reaching the theoretical rate of 625 MB per second!
Be careful, if backward compatibility is supported for USB 3.0 sockets (i.e. your device with a USB 3.0 port will work on your computer with USB 2.0 sockets), the transfer speed will remain locked to 2.0 standards …
USB standards. As early as 1995, the USB standard was developed to connect a wide variety of devices.
The USB 1.0 standard offers two communication modes:
12 Mb / s in high speed mode.
1.5 Mb / s at low speed.
The USB 1.1 standard provides some clarification to USB device manufacturers, but does not change the bit rate.
The USB 2.0 standard provides speeds of up to 480 Mbit / s.
The USB 3.0 standard provides speeds of up to 4.8 Gbps.
In the absence of a logo, the best way to determine if these are low-speed or high-speed USB devices is to consult the product documentation as long as the connectors are the same.
Compatibility between USB 1.0, 1.1 and 2.0 devices is assured. However, using a USB 2.0 device in a low speed USB port (ie 1.0 or 1.1) will limit the bit rate to 12 Mbps. Also, the operating system may display a message explaining that the stream will be restricted. .
USB port:
There are two types of USB connectors:
The so-called type A connectors, whose shape is rectangular and are generally used for low-bandwidth devices (keyboard, mouse, webcam, etc.);
The so-called type B connectors, whose shape is square and are mainly used for high-speed devices (external hard drives, etc.).
Description: USB Type A and Type B connectors
1. Power + 5V (VBUS) 100mA maximum
2. Data (D-)
3. Data (D +)
4. Ground (GND)
USB bus operation
The USB architecture has the characteristic of providing power to the peripherals it connects, up to a maximum of 15 W per device. It uses a cable consisting of four wires (GND ground, VBUS power supply, and two data wires named D- and D +).
Description: USB cable
The USB standard allows chaining of devices, using bus or star topology. The devices can then be connected one after the other or branched out.
The branching is done through boxes called “hubs”, with a single input and several outputs. Some are active (providing electrical power), others passive (powered by the computer).
Description: USB Port Bus Topology
Description: USB ports star topology
The communication between the host (the computer) and the peripherals is carried out according to a protocol (communication language) based on the principle of the Token Ring. This means that the bandwidth is temporarily shared between all connected devices. The host (the computer) sends a sequence start signal every millisecond (ms), a time interval during which it will simultaneously give the “speech” to each of them. When the host wants to communicate with a device, it sends a token (a data packet, which contains the address of the device, encoded in 7 bits) designating a device, so it is the host who decides the “dialogue” with the peripherals. If the device recognizes its address in the token, it sends a data packet (8 to 255 bytes) in response; otherwise, it forwards the packet to other connected devices. The data thus exchanged is encoded according to the NRZI encoding.
Since the address is encoded in 7 bits, 128 devices (2 ^ 7) can be simultaneously connected to such a port.