Inside USB4

Brian Benchoff
Sep 19, 2019 · 4 min read

After twenty-odd years, the USB Implementers Forum has published the design spec for USB4. Yes, it’s backwards compatible, and yes, it’s using only USB Type C connectors.

But the last decade of USB technology hasn’t been governed by logic or reason. Does your laptop have a USB Type C connector? If it does, can you connect a monitor to any of the ports? Which one? Today, you can buy a new Thinkpad, plug a monitor into one of the USB C ports, and the monitor won’t work. Plug into the other port, and the monitor turns on. Technology, as always, is stupid. What is USB4 doing to solve these problems?


The History of USB

The days before USB were dark, indeed. Modems, when we had modems, connected via a serial port, through a null-modem cable, and used a DB-25 connector. You could find another DB-25 port on your computer: the parallel port.

This was used to connect Zip drives and printers. Apple was weird, with mini-DIN connectors: you connected your modem to the port with the printer icon on it. AAUI was a weird Ethernet port, and there were at least three varieties of SCSI. God help you if you had a Sun workstation.

This all changed in 1998 with the introduction of the iMac G3. No piece of technology has been as influential as this curvaceous Bondi Blue egg.

Given the number of blog posts decrying the loss of a headphone jack on a smartphone, we can safely say the iMac would have melted people’s brains today. There was no floppy drive (!), and the SCSI, ADB, and serial ports were gone (!!). Connectivity was through a new port, a Universal Serial Bus.

This is the first computer to get rid of legacy ports and ship a device with only USB. (In fairness, there was a phone jack for the internal modem, and an Ethernet jack because USB couldn’t support the bandwidth. Firewire was in there too, and an IrDA window was right on the front of the computer, something we really wish would make a comeback.)

From then on, everything was USB. Keyboards and mice ditched the old PS/2 ports of old, all the Zip disks converted to USB, and of course you needed to buy a USB cable to connect your printer. USB just worked, and within a few years we had these things called, ‘thumb drives’. Everything was going great.

The Confusion of the Tongues

As a follow-on to USB 1.0, the USB Implementers Forum released USB 2.0 in 2001, with greatly increased bandwidth. You could get 480 Megabits per second out of this port, good enough for most uses, and any USB port would reliably give any device 5 Volts at 500 milliamps to charge just about anything. At this time, there were only four plugs: the big USB Type A (the big rectangle), USB Type B (the big square one), USB mini (the bigger small one) and USB micro (the smaller small one).

USB 3.0 changed this, with a ‘super speed’ data transfer rate. USB 3.1 popped on the scene with even faster transfer rates. USB 3.2 came along, and there’s USB 3.2 Gen 1, USB 3.2 Gen 2, and USB 3.2 Gen 2x2. The names change somewhere along the line, too, and someone had the great idea of throwing Thunderbolt into the mix. Along the way, the USB Type-C connector appeared, remarkable in that it’s reversible and can supply enough current to charge a laptop.

For a short time before the popularization of USB Type C connectors, a few companies made reversible USB Type A connectors. This is a Wurth Electronics USB receptacle, Part Number 614108247221.

But the use of USB Type C connectors doesn’t mean a device will support USB Power Delivery, or that Thunderbolt is embedded in the connector, or that the cable is certified for the full 40 Gbps of bandwidth. Add in the fact that the Raspberry Pi 4 has the wrong design for a power connector, and things are confusing, to say the least.

USB4: Fixing this mess?

But USB4 should finally solve this confusion. A few years ago, Intel gave Thunderbolt 3 to the USB Implementers Forum, paving the way for external GPUs and a single cable connected to a monitor. If manufacturers wish, they can build Thunderbolt 3 right into USB4. No, not every device with a USB4 port will support Thunderbolt 3, but it may be possible to use one cable to plug your phone into a projector.

By default, all USB4 devices will support USB Power Delivery, or USB-PD. That means everything with a USB4 port will be able to charge at up to 100 Watts, although low-power devices like a keyboard will be able to trickle-charge from a device.

USB4 doesn’t clear all the confusion surrounding USB 3, but it is a step in the right direction: it’s a single port that does what you should expect. It will be a while until devices with USB4 are on the market and some time after that until you can get a motherboard with USB4 built right in. Still, the future is coming, it’s just not here yet.

Supplyframe

Discussing the business of hardware and hardware manufacturing.

Brian Benchoff

Written by

Supplyframe

Discussing the business of hardware and hardware manufacturing.

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