With USB Type C appearing in more devices, there has been plenty of confusion with regards to what Type C is and its relation to the standards surrounding it (e.g. USB 3.1/2, Thunderbolt 3, USB PD). In order to understand USB Type C, we need to understand the USB specification itself.
Universal Serial Bus (USB) is a specification created to standardize communications between computers and peripherals (e.g. mice, keyboards, printers). The specification includes 3 parts: data, power, and connector.
The versions of USB (1.0, 1.1, 2.0, 3.0, 3.1, and 3.2 as of writing) define how data is transferred between devices and at what speed.
Newer versions of USB are designed to be backwards compatible with older versions. That is, if you have a computer that supports USB 3.0, you can connect a peripheral that supports USB 1.0/2.0 and it will work. You can also connect a computer that supports USB 1.0/2.0 and a peripheral that supports USB 3.0. The speed of the connection, however, will be limited by the device with the lower USB version.
USB Power Delivery (USB PD) defines how much power can be transferred between devices through USB cables. USB PD specifies source output power ranges as well as voltages and currents that are allowed within these ranges.
USB connectors were originally split into “Type A” and “Type B.” Type A is used for computers and Type B is used for peripherals. This was done to prevent users from connecting computers or peripherals to themselves. Both types include mini and micro sizes for devices too thin to fit a standard size port.
Connectors evolve over time, adding new wires to allow for faster speeds and higher power delivery.
These connectors were purposely made irreversible to reduce manufacturing costs. To help users determine the correct orientation, the designers of the connectors specified that the USB symbol must be printed on the “top” of plugs. Ports must be oriented so the USB symbol on the plug would face “upwards” when plugged in. This requirement, however, was not followed on some electronic devices and has gone unnoticed by most consumers, leading to a minor but frustrating inconvenience.
Type C is a connector that replaces Type A and Type B
Type C eliminates the need for specific A-to-B cables, preventing those moments when you don’t have the right cable to connect your smartphone to a charger.
In addition, Type C is small enough for thin devices, is reversible, and allows for higher speeds and power delivery (up to 100 Watts).
What is Thunderbolt 3?
If you have looked at recent laptops such as Apple’s MacBook Pro 13/15 (2016-2017 models) or Dell’s XPS 13/15 (2016-2018 models), you may have noticed that these devices have USB Type C ports that also support Thunderbolt 3. What is Thunderbolt 3, how is it different from USB, and why does it use USB Type C?
Like USB, Thunderbolt, developed by Intel and Apple, is also a specification created to standardize communications between computers and peripherals. Thunderbolt, however, is a combination of two interfaces: PCI Express and DisplayPort.
PCI Express (PCIe) is an interface created to standardize communications between CPUs and internal components (e.g. graphics cards) or storage (e.g. PCIe NVMe SSDs). It is much faster than USB.
DisplayPort is an interface used primarily for transferring audio and video. It is similar to HDMI.
Thunderbolt combines the separate signals of the above interfaces into a single signal, which is then transmitted through a Thunderbolt cable, and then separated back into separate signals at a Thunderbolt peripheral.
Thunderbolt v. USB
Compared to USB, Thunderbolt is much faster: USB 3.2 has a maximum speed of 20 Gb/s while Thunderbolt 3 has a maximum speed of 40 Gb/s.
Since Thunderbolt can transfer PCIe data, it can be used to connect unique peripherals, such as external graphics cards, that would be difficult or impossible to do so over USB.
Why Thunderbolt 3 Uses USB Type C
Thunderbolt 1 and 2 used mini DisplayPort cables. Thunderbolt 3 switched to USB Type C to gain more market share and to allow for one connector that supports multiple interfaces. Doing so also allows Thunderbolt 3 to inherit the benefits of USB Type C.
Summary
While the dongle-filled transition from traditional USB connectors to Type C may be painful, Type C is a powerful connector that is worth the investment. It points to a future where, hopefully, we can charge and connect all of our electronic devices with a single cable.
¹ Actual speeds will be lower than maximum speeds due to overhead incurred by encoding.
