An in-depth look into the history, applications, and future of the Universal Serial Bus.
The Universal Serial Bus (USB) was first introduced in late 1995 with the intent to create a standard way to transfer data and power to peripheral devices. The backwards compatibility, simplistic design, and low cost has made it the go-to option for most consumer connection needs. Almost all computers and peripheral devices built today use USBs as the standard connecter, largely replacing other relics of the past such as serial ports, proprietary charging cables, and the monstrous 25 pin parallel ports.
As the popularity of the USB grew, so did the capabilities of the connector. The latest version in the works is USB 4.0. There are now multiple types of USB connectors that vary in form factor, supported protocols, and transfer speeds.
USB Speed Standards
We have omitted the USB 1.X standards due to their lack of relevancy and usage in modern computing and peripheral devices. Modern USB standards are also backwards compatible to USB 1.1.
USB 2.0 or “Hi-Speed USB” was first introduced in 2000. USB 2.0 increased the transfer speed from 12 Mbps to 480 Mbps, providing some much-needed bandwidth for the 21st century. USB 2.0 has many of the most common USB form factors that we have all grown accustomed to, including Type-A, Type-B, USB Micro-A, USB Micro-B, USB Mini-A, and USB Mini-B. The common port color for this standard is black, although it is not uncommon to see it use USB 1.X’s standard color of white.
USB 3.0 was the third major overhaul to the USB standard first launching in 2008. This standard of USB has several associated names, including SuperSpeed, USB 3.1 Gen 1(2013), and USB 3.2 Gen 1(2017). Accompanying form factors include USB-A, USB-B, USB Micro-B, and USB-C. The data transfer speed on these iconic blue ports comes in at a mighty 5 Gbps (625 MB/s). The nearly 10X increase in transfer speed brought the USB standard over the 1 Gbit/s mark for the first time, opening the door for a whole slew of 1 gigabit network-ready USB devices. With 5 gigabits of available bandwidth, you could connect to a high-speed ethernet connection, upload videos from your SD card, and connect to your printer with a single USB hub.
USB 3.1 ultimately started the trend of unnecessarily confusing synonyms with the addition of USB 3.1 Gen 1, USB 3.1 Gen 2, and SuperSpeed+. For clarification, USB 3.0 was renamed to USB 3.1 Gen 1 and USB 3.1 Gen 2 simply provides a faster 10 gigabit transfer speed. SuperSpeed+ (SS+) is just the marketing moniker that associates the 10-gigabit transfer speed with whatever product it is being integrated with. Since its introduction in 2013, this standard has been criticized by nearly the entire computing community. There are no new form factors associated with this standard, providing the all familiar USB-A, USB-B, USB Micro-B, and USB-C. The most common port color for this standard is teal, but it can also be read, so you need to be careful and look for the sticker that says “SS/SS+/SS*” where “*” is commonly the transfer speed such as “SS10” (USB 3.1 Gen 2).
USB 3.2 continued the trend of horrible naming conventions. Released in 2017, USB 3.2-X brought us USB 3.2 Gen 1, USB 3.2 Gen 2, and USB 3.2 Gen 2×2. Before you reach for your trusty FireWire 400, USB 3.2 Gen 1 is equivalent to USB 3.1 Gen 1 (5 Gb/s) which is equivalent to the blue USB 3.0 that we have all come to know and love. USB 3.2 Gen 2 is equivalent to USB 3.1 Gen 2 (10 Gb/s) and USB 3.2 Gen 2×2 is the only new offering with a transfer speed of 20 Gb/s. The marketing moniker for USB 3.2 Gen 2×2 is SuperSpeed++. The most common associated color is red.
The adoption of USB 3.2 makes understanding form factors more important than ever. Type-A can support a maximum standard of USB 3.2 Gen 2 (10 Gb/s); this is a limitation that results from having a maximum of 9 pins in the Type-A form factor. Before the Gen 2×2 standard was released, USB-C was capped at 10 gigabit speeds. The bi-pluggable nature of the USB-C form factor was not being fully utilized by USB 3.1 because only one side of the connector (10 pins) was available for data transmission. USB 3.2 Gen 2×2 simply made the unused side available for parallel data transmission which doubled the transmission of USB 3.2 Gen 2, thus giving us USB 3.2 Gen 2×2. Unfortunately, the millions of consumers that were comparing multiple products and basing their purchasing decisions on the available USB transfer speed would have needed in-depth knowledge of the many USB form factors and pinouts to make sense of the USB 3.2 Gen 2×2 standard at first glance.
In conclusion, USB Type-A can support up to USB 3.2 Gen 2 SuperSpeed+ (10 Gb/s) and USB-C can support up to USB 3.2 Gen 2×2 SuperSpeed++ (20 Gb/s), barring more advanced protocols such as Thunderbolt 3 that we will discuss in another article.
USB Form Factors (Connector type)
Nearly ubiquitous now, what many people know as a USB is really a Type-A connector. The Type-A is typically used to connect a host to a client. The flat, rectangular shape uses friction-based compression tabs to hold the connector in place, creating a quick and easy connection. Although the male version of the type A was popularized through its use on USB thumb drives, the Type-A has both a female and male configuration. One popular use of the female Type-A is connecting peripherals to a host computer. It is important to note that Type-A is simply a form factor and can have either 4 or 9 pins located within the connector which dictates the speed and capability of the connector.
The Type-B connector is intended for use on peripheral devices. The shape of this connector is smaller than the Type-A in length but taller in width. It has a squarish shape with a flat top. Like the Type-A, this connector also uses friction to hold the connector in place. Most Type-B cables come configured with a male Type-B on one end and a male Type-A to connect to the host. Type-B connectors are also available in either a male or female interface. The form factor for Type-B was changed at the same time as the update from USB 2.0 to 3.0. Even at the time of writing, 2021, the USB Type-B 3.0 is uncommon seeing that many peripheral devices cannot take advantage of the increased bandwidth. Likely, your only dealing with the Type-B is via a wired printer or perhaps an oversized external hard drive dock.
Created to support smaller devices, higher speeds, and greater versatility, the USB C is perhaps the most capable and most confusing form factor in the USB family. The USB C is diminutive in size when compared to a Type-B. Moreover, the USB C is small enough to be used with phones and versatile enough for bigger devices such as laptops. Many users’ first encounter with the Type-C form factor was likely through the primary charging ports on android devices.
The innovative USB C form factor allows it to be plugged in with either orientation, making it the only one in the family that can be easily connected in the dark. The orientation duality is also the reason that the USB C is the only connector to support USB 3.2 Gen 2 2×2 20 Gb/s (2×2 = 2 per side of the connector). Network administrators and computer architecture enthusiasts can think of the 2×2 standard as the USB version of LAG groups.
Many new consumer devices have already begun eliminating USB A and RJ45 Ethernet ports in favor of a do-it-all USB C. Some of the protocols that can be transmitted within the Type C form factor include PD charging, HDMI 2.1, DP 2.0, 1000base-T (gigabit) and 10GbaseT (10 gigabits) Ethernet, USB 4.0, Thunderbolt 4. USB C can also be easily adapted for legacy interfaces such as Serial (RS232, RS422, RS485) and display connectors such as DVI-I and DVI-D (assuming the USB C port supports display output).
The oldest of the Minis, USB B Mini is a form factor commonly used to support smaller peripheral devices such as older phones, MP3 players, tablets, digital cameras, and USB hubs. It does not stand up to thousands of repeated plug/unplug cycles, so it is often used for low-stress applications. USB B Mini was rated for speeds up to USB 2.0 (480 Mb/s).
Type-A Mini was created in response to hosts getting smaller with the adoption of more mobile devices. Most common is the Mini A male to standard A female for On-The-Go (OTG) devices. Mini connectors were superseded by the new smallest USB, USB Micro.
USB Micro-A supports the same devices as the mini A but in a smaller form factor. It has replaced the mini on most of the newer OTG devices such as smartphones and tablets. This connector is special because it can accommodate Type-A Micro and Type-B Micro in its AB port.
USB Micro-B is found on many semi-modern Android devices and peripheral devices. It is also the de facto choice for wireless chargers and external battery packs. It has a different form factor for USB 2.0 and USB 3.0+, so there can be compatibility issues. The Micro B is often criticized for its poor durability and poor performance in connection cycle tests.
The Future of USB
The new kid on the block. This specification was released in August of 2019 based largely on Intel’s Thunderbolt 3 spec. The data transfer speed is 40 Gbit/s, compatible with Thunderbolt 3 devices (not guaranteed), and backwards compatible with USB 2.0 and 3.2 (including 3.1 and 3.0). The USB 4 standard will only be offered via the USB C form factor. With regards to display output, the 4.0 standard will support DisplayPort Alt Mode with DP 2.0 compatibility. Finally, USB 4.0 has adopted the port tunneling architecture from Thunderbolt 3 to efficiently load balance parallel PCIe, DB, and USB data streams. Finally, and perhaps the most exciting feature, is the move from the SuperSpeed marketing jargon to labeling ports with “USB 40 Gbps”! This will be the first major USB revision that will use numbers to make the port type and speed more easily identifiable.