2023 USB-C hub on a 2004 PC

[isaacschemm]

Recently I bought a travel hub for my laptop (up 'til now, I'd been using my work laptop's Thunderbolt dock, but I thought it would be nice to have something I could bring with me.) It has a USB-C plug and a small collection of ports:

• Left:
  
• HDMI out
• SD and microSD card reader
• USB-C (power input)
• Right:
  
• USB-C (not Thunderbolt)
  
• USB-A (2x)
  

These sorts of hubs have become widespread with the rise of laptop computers (and tablets/smartphones) with nothing but USB-C ports. USB-C is still seen as something of a new, shiny technology (after all, it didn't even exist ten years ago!) So out of curiosity, and a sense of playfulness, I decided to try plugging the hub into my Dell Dimension 4700, a computer designed almost twenty years ago.

The HDMI port didn't do anything, of course, but everything else worked almost perfectly.

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In 2004, it was the early days of PCI Express, and the Dimension 4700 came with two PCI Express slots: a long slot for the graphics card, and a spare one-lane slot. And since PCI Express is, of course, still a thing, it's not hard to get your hands on a PCIe card that gives you a couple of USB 3 slots... and then add a front panel with USB-A and USB-C ports. (After all, USB-C at its core - if you're not using any alternate modes - is still USB, maybe with a bit of extra circuitry for detecting plug rotation.) My PCIe card uses a VL805 chip and provides a header for the front panel to connect to, along with a power input - otherwise, the 4700 doesn't give enough power over PCIe to run the card, the front panel, and a spinning disk hard drive. (I bought this card after learning that - but the old card found a home in a relative's PC, to add a couple extra ports to the back.)

The USB-C connector normally provides pins for a USB 2.0 link and two USB 3.x links, but if DisplayPort Alternate Mode is used, one or both of the USB 3.x links can be repurposed for a DisplayPort connection. This explains why you see a similar port selection on so many of these hubs, and why you can't just plug another HDMI or DisplayPort adapter into the USB-C data port on them. I imagine the only real logic the hub has to handle is power delivery (whether from an external source or from the host device) - everything else can be built from just a hub (using the USB 3 link and the USB 2 link), a card reader (attached over USB), and a DisplayPort to HDMI adapter, all of which are commonplace.

Thunderbolt docks work differently. There's a lot more active circuitry in those - it lets you have a higher bandwidth connection (and the flexibility to daisy-chain another Thunderbolt or USB-C device), but it's really working at a higher / more abstract level in order to make that happen. Not surprising that the Thunderbolt dock does nothing when plugged into the 4700!