Everything You Need to Know About the Thunderbolt Connection

[nextpage title=”Introduction”]
Thunderbolt (formerly known as “Light Peak”) is an external connection that allows 10 Gbps (around 1 GB/s) of data transfer in each direction. In this tutorial, we will explain everything you need to know about it.
The main advantages of Thunderbolt are the use of existing protocols, instead of creating a new one, and the use of existing connector types. Because it uses existing protocols, it is not necessary to install an additional driver on your PC in order to use a Thunderbolt connection, and as it uses existing connector types, it is compatible with devices that use the same connector type, even if they are not Thunderbolt.

Figure 1: the Thunderbolt architecture

All versions of the Thunderbolt connection work with the PCI Express and DisplayPort protocols, while Thunderbolt 3 added USB 3.1 and 10G Ethernet to the list. Therefore, it can carry either computer data (using PCI Express, USB 3.1 or 10G Ethernet), or digital video (using the DisplayPort protocol). This means that the other end of the cable can be attached to either an external storage device such as a DAS (Direct Attached Storage) box featuring a Thunderbolt port or to a video monitor with a Thunderbolt port. Since the cable can carry both video and data, the video monitor must have a Thunderbolt chip in order to capture the video data; regular monitors using a DisplayPort or a mini DisplayPort connector won’t work directly with Thunderbolt. It is possible that manufacturers will release an external box with a Thunderbolt controller in order to allow a connection on regular video monitors.

Figure 2: how Thunderbolt works

[nextpage title=”Standards”]

Currently, there are three Thunderbolt generations available, simply called 1, 2, and 3.
The first Thunderbolt connection has four 5.4 Gbps DisplayPort channels, two used for data transmission and two used for data reception, thus generating one 10 Gbps transmission channel and one 10 Gbps reception channel. Thunderbolt 2 doubles the transfer rate by allowing the four channels to be joined in the same direction. Functionally, the first two generations are identical, and both make use of mini DisplayPort (mini DP) connectors.
The third generation, however, brought some important new features. Besides doubling the bandwidth in relation to the previous generation, by doubling the number of DisplayPort channels available and using the PCI Express 3.0 standard, it supports USB 3.1 connection and makes use of the type C USB connector instead of the mini DisplayPort. Therefore, Thunderbolt 3 connections are compatible with USB 3.1 devices. However, when connected to USB 3.1 devices, the Thunderbolt connection is limited to 10 Gbps (1 GB/s), which is the maximum transfer rate of the USB 3.1 bus. Additionally, Thunderbolt 3 allows the creation of 10G Ethernet networks and is able to provide up to 100 W without an external power supply.
The first two Thunderbolt versions allow up to seven devices per port, while the third version the maximum number of devices per port was reduced to six. It is possible to use up to two video monitors at the same time.

Thunderbolt Specs by Version

Generation	Maximum bandwidth (Gbps)	Maximum bandwidth (GB/s)	Devices	Compatibility
1	10 Gbps	1 GB/s	7	PCIe 2.0 x4, DP 1.1a x4
2	20 Gbps	2 GB/s	7	PCIe 2.0 x4, DP 1.2 x4
3	40 Gbps	4 GB/s	6	PCIe 3.0 x4, DP 1.2 x8, USB 3.1, 10G Ethernet

Thunderbolt 3 is still compatible with DisplayPort, but since now it uses a different connector type, an adapter is required. Because of the higher available bandwidth, it is possible to connect up to two 4K (4096 x 2160 x 30 bits) at 60 Hz video monitors, one 4K at 120 Hz video monitor, or one 5K (5120 x 2800 x 30 bits) at 60 Hz video monitor using a Thunderbolt 3 connection.
[nextpage title=”Cables and Connectors”]
As mentioned, Thunderbolt 1 and 2 use a mini DisplayPort (mini DP) connector. In Figure 3, you can see a Thunderbolt 1 port on a motherboard.

Figure 3: Thunderbolt 1 port on a motherboard

There are two types of cables for Thunderbolt 1 and 2: electrical or optical. Electrical cables can be anywhere between 4 inches and 9.8 feet (10 cm to 3 m) long, while optical cables can be between 32.8 feet and 65.6 feet (10 m to 20 m) long. The use of one kind of cable or the other will depend on the cable length you want.
One advantage of the Thunderbolt 1 and 2 connections is that both electrical and optical cables use the same connector type, the mini DisplayPort (mini DP). This is an electrical connector, so optical cables have circuitry at both ends to convert electrical signals into optical signals and vice versa. This circuit is available inside the rectangular box where the connector is attached. See Figure 6. Because of that, optical cables will not be inexpensive.

Figure 4: Thunderbolt 1 electrical cable