Most recent higher-end laptops seems to have a Thunderbolt 3 connection. However, this does not seem to be case for recent motherboards or graphics cards for desktop computers.
I know that one application of Thunderbolt 3 is connecting external GPUs, which is a laptop-specific need. However, Thunderbolt 3 has other uses as well:
- Seems to provide access to the PCI Express bus in general (although I do not know whether there is any other practical application for this than external GPUs).
- Can provide a high-bandwidth video signal for external displays.
At least the latter would seem to be useful on desktop computers as well. Why is Thunderbolt a mostly laptop-only technology then?
22 Answers
It is not so much being a laptop-only technology but rather it just being that motherboards for desktop computers usually have multiple PCI-Express slots.
PCI-Express has many different hardware protocols and most motherboards for desktop computers often have;
- At least one PCI-E x16/x8/x4 slot that is utilised by graphics cards, which already use the hardware standard outputs for current display input standards (HDMI/DVI-D/Display Port) and,
- At least one PCI-E x1 slot for utilisation by storage expansions peripherals that use SATA Express or NVM Express.
Here are a few reasons why Thunderbolt 3 is not that popular with desktop computers:
Desktop computers usually come with of multiple PCIe slots providing plenty of flexibility when it comes to upgrading. For many applications installing a PCIe card might be more elegant (less cables and boxes on the desk) than connecting an external device using Thunderbolt 3. If an external device is desired today, USB 3 is often sufficient.
Thunderbolt 3 needs quite a few PCIe lanes to connect to the CPU (up to 4 PCIe lanes can be transmitted through Thunderbolt 3). Thus offering a few Thunderbolt 3 ports might drive up the price. Price is key in most parts of the main-board market. Note that a few main-board manufacturers sell expansion cards that add Thunderbolt 3, though.
Each Thunderbolt 3 port is supposed to provide at least 15 W power to connected devices. Even x4 and wider PCIe expansion cards are limited to a total power consumption of 25 W. A dual Thunderbolt 3 card thus would need an additional power cable from the PCs power supply to provide 15 W to each port. A x16 slot can provide more power but it's usually occupied by the video card.
Thunderbolt 3 is supposed to carry video signals which on a modular desktop computer usually emerge from a discrete video card or a connector at the rear of the main board. The video signal has to be routed from the DisplayPort output of the graphics card into the expansion card where the Thunderbolt 3 controller combines it with the USB/PCIe signal to Thunderbolt 3. The length of the required cable can be very different for integrated graphics vs. PCIe video cards - not the most elegant solution.
All this is much easier in a laptop where all components are fixed and soldered onto the same board.
