What is the difference between USB 3.1 Gen 1 | Gen 2 and USB 3.2? 

The USB-IF organization can be said to be the favorite organization to change its name.

Although the commercial naming method of USB 3.x/USB4 has been deleted, and the naming method of USB 3.X and USB4 will be changed to “USB+transmission speed”, but now There are still many old machines in use, keeping the name of the most confusing USB 3.x period.

Here we review the most confusing ones. What are the differences between USB 3.1 Gen 1, Gen 2 and USB 3.2?

USB 3.x started with the launch of the USB 3.0 specification in 2008, and has successively experienced four different versions, including USB 3.1 Gen1, USB 3.1 Gen2, and the latest USB 3.2.

There are also some differences in data encoding methods, resulting in different theoretical transmission speeds, so let’s take a closer look at the details.

Encoding to avoid signal interference

When the USB Implementers Forum formulated the USB 3.0 specification, the data transfer rate was set at 5Gbps. Later, when USB 3.1 was launched, USB 3.0 was renamed USB 3.1 Gen1, so the two are actually the same technology.

As for the newly launched upgraded specification, it is named USB 3.1 Gen2, which doubles the data transmission rate from 5Gbps to 10Gbps, and changes the encoding method used to further improve the actual transmission performance. 

As for the latest USB 3.2, two USB 3.1 Gen1 or Gen2 data lines are used for dual-channel transmission.

However, in order to reduce the electromagnetic wave interference generated during data transmission, each generation of specifications will first encode the data before sending it out.

When USB 3.1 Gen1 is in operation, the 8-bit data will be encoded by 8b/10b, scrambled into 10-bit symbols (Symbol), and the coded symbols will be transmitted with spread spectrum technology (Spread Spectrum) , to reduce the situation of electromagnetic wave interference.

 After receiving the signal, the receiving end can restore the 10-bit symbol to 8-bit data through the decoding process.

However, USB 3.1 Gen2 abandons the 8b/10b encoding and uses the 128b/132b encoding derived from the 64b/66b encoding used in 10GbE Ethernet. 

This kind of encoding will form 16 groups of 8-bit data into a frame (Frame), and add a 4-bit identification code (Identifier) ​​at the front of the block. Spread spectrum technology will still be used during transmission, but it can be broken up depending on the situation.

After receiving the signal, the receiving end will restore the 132bit frame to 128bit data.

Gen2 can reduce transmission loss

The biggest difference between Gen1 and Gen2 is that the codes used are different, and the losses generated during transmission are also different. In the case of Gen1, for every 10 bits of traffic transmitted, only 8 bits are real data, and the loss is as high as 20%. 

In Gen2, for every 132 bits of traffic transmitted, there are 128 bits of real data, and the loss is only about 3%.

Therefore, when calculating the theoretical transmission speed, the calculation method of USB 3.0 and USB 3.1 Gen1 is as follows:

And USB 3.1 Gen2 is calculated as follows:

10Gbps (data transfer rate) x 128/132 (transmission loss deducted) = 9,696Mbps (theoretical transfer speed) = 1,212MB/s

As for the case of USB 3.2, it is the simplest, because it uses two USB 3.1 Gen1 or Gen2 data channels, so just multiply by 2 times, the calculation method is as follows:

However, the speeds mentioned here are all theoretical values.

In actual application, it will be affected by factors such as wire material, terminal quality, signal interference, and even device performance. According to experience, at least a 20% discount will be the actual speed.

Therefore, It is not surprising that the performance of the USB device tested in the future is not as fast as the official claimed speed.