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USB 4: What to Expect and What We Know
Staff Writer

It has been over two decades since the iMac G3 became the first mass-market personal computer to incorporate Universal Serial Bus (USB) ports into its design. For those old enough to remember, USB replaced a whole range of serial and parallel ports that were used to connect computer peripherals such as monitors, keyboards, and other I/O devices. Different types of devices were manufactured with many different types of ports and compatibility between computers and peripherals was a constant issue. The USB standard changed all of this by establishing a "universal" port that could be used for all kinds of peripherals. 

Having gone through several iterations, the latest version of the USB standard known as the "Universal Serial Bus 4 (USB4™) Specification" was published in August 2019 by the USB-IF Promoter Group, an industry group with representation from Apple, Hewlett-Packard, Intel, Microsoft, STMicroelectronics, and Texas Instruments. Once again, the world's leading electronics firms have collaborated to bring us a new standard for USB that promises greater compatibility and even faster speeds.

With the first USB4 connector cables slated for release in 2021, we're using this week's blog post to take a closer look at what we've already learned and what we can expect from the USB 4.0 specification release. We'll cover the history of USB, new features that have been announced for USB4 and any additional details or rumors of what to expect from the upcoming release.

The History of USB

For younger readers, it might be difficult to appreciate just how different computing was before the introduction of USB. Prior to the 1995 publication of the USB standard, electronics manufacturers who built peripherals for computers faced major device compatibility challenges. Without a standard port design for peripherals, it was impossible to build a mouse or keyboard that would work on every machine. For consumers, it was a constant struggle to purchase compatible peripherals and a new computer purchase might require the user to swap their mouse, keyboard, and monitor with newly compatible replacements.

1995-1999: USB 1.0

The USB 1.0 standard was first published in 1995, offering data transfer speeds of up to 12 megabits per second. The familiar USB connector design was also released during this period, with its recognizable male and female connectors. It was 1998 when the iMac G3 become the first PC to include USB ports. Standardized porting meant that peripherals manufacturers could finally build products that would work for all consumers, regardless of what type of computer they used. Computer manufacturers rapidly adopted the USB port design for inclusion in their products.

2000-2007: USB 2.0

USB 2.0 had a profound effect on the world of computing. This was the first USB standard that included power options (users would soon use USB connector cables to charge their cell phones). The emergence of USB flash drives rendered floppy discs, compact discs, and DVDs obsolete as storage media, thanks to their minuscule size and high storage capacity. 

black usb drive USB flash drives like this one largely replaced floppy discs and compact discs in the early 2000s as the most popular portable data storage media. The USB Type-A connector shown here has now been replaced by the reversible USB Type-C connector. Photo by charlesdeluvio on Unsplash

2008-2017: USB 3.0 & 3.1

In 2008 the USB 3.0 specification was published and later followed by the USB 3.1 standard.  These standards were necessary to ensure that consumers would benefit from advancements in technology that enabled greater data transfer speeds and other capabilities. USB 3.0 offered data rates of up to 5 Gbps, while the USB 3.1 upgrade offered a maximum speed of 10 Gbps. The USB Type-C connector cable was also introduced during this time period (in 2014, to be precise). USB Type-C offers a user-friendly reversible connector, but it may be adopted more slowly because of the ubiquity of USB Type-A and Type-B ports.

2017: USB 3.2

Released in 2017, the USB 3.2 standard is the first iteration that uses the USB Type-C connector. Transfer speeds of up to 20 Gbps make USB 3.2 the most powerful specification so far in terms of data transfer speed. The new SuperSpeed+ transfer mode was made possible by allowing multi-lane operation over existing wires that were meant to support the reversible design feature of the Type-C connector. The release of USB 3.2 also resulted in naming and branding changes for previous USB versions.

2021: USB 4.0

This brings us to the USB 4.0 standard. Released in August 2019, USB4 is based on the Thunderbolt 3 protocol specification developed by Intel. USB4 will support 40 Gbps throughput and new features that will enable high-speed data transfer with multiple end devices.

USB4 and Thunderbolt Compatibility

Since the release of USB 3.0, each new iteration of the USB standard has had increased bandwidth as its most important feature. In establishing USB4, the USB Implementer’s Forum sought to increase bandwidth even further and drive the adoption of the USB Type-C connector while minimizing user confusion. These aims resulted in the establishment of four design objectives outlined in the standard:

  1. Offer display, data, and load/store functionality over a single USB Type-C connector.
  2. Retain compatibility with existing ecosystem of USB and Thunderbolt products.
  3. Define port capabilities for predictable and consistent user experience.
  4. Provide increased host flexibility to configure bandwidth, power management, and other performance-related parameters for system needs.

Intel donated the specs for Thunderbolt 3 to the USB 4.0 project because its massive 40 Gbps throughput speeds were desirable for a range of applications, including storage, displays, and low-latency connections to peripherals. Despite this, not all USB4 devices will take advantage of Thunderbolt compatibility. It will be left to manufacturers to decide whether to build in compatibility with Thunderbolt or not. The caveat is that manufacturers who wish to advertise their products as Thunderbolt 3.0-compatible may require costly hardware validation from Intel before use of the trademark is permitted.

USB4 High-Speed Capabilities 

One of the design objectives for the USB 4.0 standard was to allow for flexible bandwidth configuration. This means that devices using USB4 may not take advantage of the maximum 40 Gbps signalling rate available - they may be built for 20 Gbps or even 10 Gbps signalling and users may require more sophisticated dual-lane cables to support greater transfer speeds. Users will have to shop carefully to ensure that specs for any USB4 devices match their specifications.

The best news about USB4 might be that it mandates support for the USB power delivery protocol across all devices. The protocol involves smartly negotiated power transfer rates to USB-powered devices, which should result in longer battery life, faster charges, and extended lifetime for frequently charged batteries. 


 The USB standard represents a significant effort on the part of electronics manufacturers to provide an integrated and consumer-friendly ecosystem for connecting computers with data storage, I/O, and other peripherals. USB4 introduces a range of upgrades that support this, including mandatory support for the USB power delivery protocol, Thunderbolt compatibility, and a robust 40 Gbps maximum bandwidth.

At Total Phase, we build products that support embedded engineers throughout product development, testing and debugging, and through to market release. Our Beagle USB 5000 v2 SuperSpeed Protocol Analyzer is a non-intrusive monitoring solution for product developers that offers complete transparency into the functioning of your device and helps streamline the debugging and software testing process.   We also offer the USB Power Delivery Analyzer for debugging communication on CC1 and CC2 during power contract negotiation.

Are you designing an embedded system or connected device that leverages the USB protocol? Learn how our diagnostic tools can help you save money in product testing and get to market even faster.

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