The Ultimate Guide to USB4 From 40Gbps Speed, Dynamic Bandwidth to Full-Function One-Cable Connection
Since the emergence of USB4, we have been publishing numerous articles and links to share relevant information. However, the popularity has been so high that people everywhere are asking about the USB4 market. Starting from the early USB 1.0 era and the 1.5Mbps data transmission interface, USB has gone through multiple generations. There have been multiple specifications such as USB 1.0, USB 2.0, and USB 3.0, and the interface shapes and design schemes have included USB Type-A, USB Type-B, and the currently most common USB Type-C, etc. USB4 not only has a faster transmission speed but also has better compatibility (supporting backward compatibility, that is, compatibility with lower versions). It can connect almost all devices more efficiently and charge them. If your phone, computer, monitor, printer, etc. all support USB4, then theoretically, you only need a data cable that supports USB4 to connect the devices, making home office much more convenient. You no longer need to buy various interface conversion cables. Therefore, USB4 can make our working mode more diverse and convenient. In addition, another remarkable feature of USB4 is that it is expected to be applied in edge devices that support artificial intelligence computing.
01 USB4 vs. USB3.2
USB 3.2 is a new standard released by the USB-IF organization. It was actually introduced as early as September 2017. From a technical perspective, USB 3.2 is an improvement and supplement to USB 3.1. The core change is that the data transmission speed has been increased to 20 Gbps, and the interface still follows the Type-C scheme established in the USB 3.1 era, no longer supporting Type-A and Type-B interfaces. Both USB4 and USB3.2 use Type-C interfaces, but USB4 is much more complex. USB4 supports simultaneous transmission and reception of host-to-host, PCI Express® (PCIe®), DisplayPort audio/video, and USB data through the same Type-C interface on the same link. Two USB4 hosts can exchange IP data packets through the host-to-host tunnel; DisplayPort and USB tunnel transmission means that audio, video, data, and power can be transmitted through the same interface, which is much faster than using USB3.2. In addition, PCIe tunnel transmission can provide high bandwidth, low latency, and achieve high throughput for large-capacity storage, edge artificial intelligence, and other use cases.
USB4 integrates two transmission and reception channels into a single USB-C interface, with a rate of up to 20 Gbps and 40 Gbps, and each channel can have a data rate of approximately 10 Gbps or 20 Gbps. For chip developers, this data is very important. They need to know that in the Thunderbolt3 mode, the data rate on each transmission and reception channel is 10.3125 Gbps or 20.625 Gbps. In the traditional USB mode, only one transmission/reception channel runs at a rate of 5 Gbps (USB3.0) or 10 Gbps (USB3.1), while the two channels of USB3.2 run at a rate of 10 Gbps.
In terms of durability, the force-bearing components of the Type-C interface are mainly the external metal casing, which is stronger and less prone to damage. The central data channel is protected by an arc-shaped cover, making it difficult to be damaged. The design requirements indicate that the USB Type-C can withstand more than 10,000 plug-ins and unplugs without being damaged. If calculated based on 3 plug-ins and unplugs per day, the USB Type-C interface can be used for at least 10 years.
02 Accelerated Deployment of USB4
After the official release of the USB 3.2 protocol, the USB organization promptly announced the specifications of USB 4 within a short period of time. Unlike previous standards such as USB 3.2, which were based on the USB's own protocol, USB 4 no longer adopts the USB specifications at its fundamental level but instead adopts the Thunderbolt 3 protocol that Intel has fully disclosed. This is the biggest change in the development of USB over the past several decades. When using a Type-C connector for connection, the functions of USB4 replace those of USB 3.2, and USB 2.0 can run simultaneously. USB 3.2 Enhanced SuperSpeed remains the basic infrastructure for "USB data" transmission on the USB 4 physical line. The biggest difference between USB4 and USB 3.2 lies in that USB4 is connection-oriented. USB4 is designed with tunnels to jointly transmit data from multiple protocols on a single physical interface. Thus, the speed and capacity of USB4 can be dynamically shared. USB4 can support other display protocols or host-to-host communication while data transmission is ongoing. Additionally, USB4 has increased the communication speed from 20 Gbps (Gen2x2) of USB 3.2 to 40 Gbps (Gen3x2) on the same dual-lane, dual-simplex architecture.
USB4 not only achieves high-speed USB (based on USB3), but also defines display tunnels based on DisplayPort and load/store tunnels based on PCIe.
Display aspect: The display tunnel protocol of USB4 is based on DisplayPort 1.4a. DP 1.4a itself supports 8k at 60Hz or 4k at 120Hz. The USB4 host needs to support DisplayPort on all downstream ports. If you use the USB 4 port to simultaneously transmit video and data, the port will allocate bandwidth accordingly. Therefore, if the video only requires 20% of the bandwidth to drive your 1080p monitor (which is also a hub), then the remaining 80% of the video can be used to transfer files from an external SSD.
In terms of PCIe tunnels: The support for PCIe by USB4 hosts is optional. USB4 hubs should support PCIe tunnels and an internal PCIe switch should be present.
An important part of the USB 4 specification is the ability to dynamically adjust the amount of resources available when sending video and data through the same connection. So, suppose you have a maximum of 40 Gbps USB 4 and are copying large files from an external SSD and outputting to a 4K display. Suppose the video source requires approximately 12.5 Gbps. In this case, USB 4 will allocate the remaining 27.5 Mbps to the backup drive.
USB-C introduces "alternative mode", which is the ability to transmit DisplayPort/HDMI video from a Type-C port. However, the current 3.x specification does not provide a good method for splitting resources. According to Saunders, the DisplayPort alt mode can precisely divide the bandwidth between USB data and video data into 50/50, while the HDMI alt mode does not allow the simultaneous use of USB data.
USB4 defines a standard of 40Gbps, enabling dynamic sharing of bandwidth so that a single data cable can fulfill multiple functions. With USB4, it is possible to simultaneously transmit PCIe and display data over a single line, along with traditional USB functions, and even provide power (via USB PD) in a very convenient manner. In the future, most peripheral devices, whether it's high-speed networks, external graphics cards, high-definition displays, large-capacity high-speed storage devices, or even one machine and another machine, can be interconnected through a Type-C interface. Moreover, if these devices implement USB4 Hub, you can also connect more devices in series or branches from these devices, which is extremely convenient.
Post time: Oct-20-2025
