USB 3: How did it end up being so messy?

After this blog post’s proposed topic had already been approved, but shortly before I started to write, I realized I’d recently wasted a chunk of money. I’m going to try to not let that reality “color” the content and conclusions, but hey, I’m only human…

Some background: as regular readers may recall, I recently transitioned from a Microsoft Surface Pro 5 (SP5) hybrid tablet/laptop computer:

to a Surface Pro 7+ (SP7+) successor:

Both computer generations include a right-side USB-A port; the newer model migrates from a Mini DisplayPort connector on that same side (and above the USB-A connector) to a faster and more capable USB-C replacement.

Before continuing with my tale, a review: as I previously discussed in detail six years ago (time flies when you’re having fun), bandwidth and other signaling details documented in the generational USB 1.0, USB 2.0, USB 3.x and still embryonic USB4 specifications are largely decoupled from the connectors and other physical details in the USB-A, USB-B, mini-USB and micro-USB, and latest-and-greatest USB-C (formally: USB Type-C) specs.

The signaling and physical specs aren’t completely decoupled, mind you; some USB speeds are only implemented by a subset of the available connectors, for example (I’ll cover one case study here in a bit). But the general differentiation remains true and is important to keep in mind.

Back to my story. In early June, EDN published my disassembly of a misbehaving (on MacOS, at least) USB flash drive. The manufacturer had made the following performance potential claims:

USB 3.2 High-Speed Transmission Interface

 Now there is no reason to shy away from the higher cost of the USB 3.2 Gen 1 interface. The UV128 USB flash drive brings the convenience and speed of premium USB drives to budget-minded consumers.

However, benchmarking showed that it came nowhere close to 5 Gbps baseline USB 3.x transfer rates, far from the even faster 10 and 20 Gbps speeds documented in newer spec versions:

What I didn’t tell you at the time was that the results I shared were from my second benchmark test suite run-through. The first time I ran Blackmagic Design’s Disk Speed Test, I had connected the flash drive to the computer via an inexpensive (sub-$5 inexpensive, to be exact) multi-port USB 3.0 hub intermediary.

The benchmark site ran ridiculously slow that first time: in retrospect, I wish I would have grabbed a screenshot then, too. In trying to figure out what had happened, I noticed (after doing a bunch of research; why Microsoft obscures this particular detail is beyond me) that its USB-C interface specified USB 3.2 Gen2 10 Gbps speeds. Here’s the point where I then over-extrapolated; I assumed (incorrectly, in retrospect) that the USB-A port was managed by the same controller circuitry and therefore was capable of 10 Gbps speeds, too. And indeed, direct-connecting the flash drive to the system’s USB-A port delivered (modestly) faster results:

But since this system only includes a single integrated USB-A port, I’d still need an external hub for ongoing use. So, I dropped (here’s the “wasted a chunk of money” bit) $40 each, nearly a 10x price increase over those inexpensive USB 3.0 hubs I mentioned earlier, on the only 10 Gbps USB-A hub I could find, Orico’s M3H4-G2:

I bought three of them, actually, one for the SP7+, one for my 2018 Mac mini, and the third for my M1 Max Mac Studio. All three systems spec 10 Gbps USB-C ports; those in the latter two systems do double duty with 40 Gbps Thunderbolt 3 or 4 capabilities. The Orico M3H4-G2 isn’t self-powered over the USB connection, as was its humble Idsonix precursor. I had to provide the M3H4-G2 with external power in order for it to function, but at least Orico bundled a wall wart with it. And the M3H4-G2’s orange-dominant paint job was an…umm…“acquired taste”. But all in all, I was still feeling pretty pleased with my acquisition…

…until I went back and re-read that Microsoft-published piece, continuing a bit further in it than I had before, whereupon I found that the SP7+ USB-A port was only specified at 5 Gbps. A peek at the Device Manager report also revealed distinct entries for the USB-A and USB-C ports:

Unfortunately, my MakerHawk Makerfire USB tester only measures power, not bandwidth, so I’m going to need to depend on the Microsoft documentation as the definitive ruling.

And, of course, when I went back to the Mac mini and Mac Studio product sheets, buried in the fine print was indication that their USB-A ports were only 5 Gbps, too. Sigh.

So, what had happened the first time I tried running Blackmagic Design’s Disk Speed Test on the SP7+? My root-case guess is a situation that I suspect at least some of you’ve also experienced; plug in a USB 3.x peripheral, and it incorrectly enumerates as being a USB 1.0 or USB 2.0 device instead. Had I just ejected the flash drive from the USB 3.0 hub, reinserted it and re-run the benchmarks, I suspect I would have ended up with the exact same result I got from plugging it directly into the computer, saving myself $120 plus tax in the process. Bitter? Who, me?

Here’s another thought you might now be having: why does the Orico M3H4-G2 exist at all? Good question. To be clear, USB-A optionally supports 10 Gbps USB 3 speeds, as does USB-C; the only USB-C-specific speed bin is 20 Gbps (for similar reasons, USB4 is also USB-C-only from a physical implementation standpoint). But my subsequent research confirmed that my three computers weren’t aberrations; pretty much all computers, even latest-and-greatest ones and both mobile and desktop, are 5 Gbps-only from a USB-A standpoint. Apparently, the suppliers have decided to focus their high-speed implementation attention solely on USB-C.

That said, I did find one add-in card, Startech’s PEXUSB311AC3, that implemented 10 Gbps USB-A:

I’m guessing there might also be the occasional motherboard out there that’s 10 Gbps USB-A-capable, too. You could theoretically connect the hub to a 10 Gbps USB-C system port via a USB-C-to-USB-A adapter, assuming the adapter can do 10 Gbps bidirectional transfers, too (I haven’t yet found one). And of course, two 10 Gbps USB-A-capable peripherals, such as a couple of SSD storage devices, can theoretically interact with each through the Orico hub at peak potential speeds. But suffice it to say that I now more clearly understand why the M3H4-G2 is one-of-a-kind and therefore pricey, both in an absolute sense and versus 5 Gbps-only hub alternatives.

1,000+ words in, what’s this all have to do with the “Why is USB 3 so messy” premise of this piece? After all, the mistake was ultimately mine in incorrectly believing that my systems’ USB-A interfaces were capable of faster transfer speeds than reality afforded. The answer: go back and re-scan the post to this point. Look at both the prose and photos. You’ll find, for example:

• A USB flash drive that’s variously described as being “USB 3.0” and with a “USB 3.2 Gen 1” interface and a “USB 3.2 High-Speed Transmission Interface”
• An add-in card whose description includes both “10 Gbps” and “USB 3.2 Gen 2” phrases
• And a multi-port hub that’s “USB 3.1”, “USB 3.1 Gen2” and “10Gbps Super Speed”, depending on where in the product page you look.

What I wrote back in 2018 remains valid:

USB 3.0, released in November 2008, is once again backwards compatible with USB 1.x and USB 2.0 from a transfer rate mode(s) standpoint. It broadens the pin count to a minimum of nine wires, with the additional four implementing the two differential data pairs (one transmitter, one receiver, for full duplex support) harnessed to support the new 5 Gbps SuperSpeed transfer mode. It’s subsequently been renamed USB 3.1 Gen 1, commensurate with the January 2013 announcement of USB 3.1 Gen 2, which increases the maximum data signaling rate to 10 Gbps (known as SuperSpeed+) along with reducing the encoding overhead via a protocol change from 8b/10b to 128b/132b.

 Even more recently, in the summer of 2017 to be exact, the USB 3.0 Promoter Group announced two additional USB 3 variants, to be documented in the v3.2 specification. They both leverage multi-lane operation over existing cable wires originally intended to support the Type-C connector’s rotational symmetry. USB 3.2 Gen 1×2 delivers a 10 Gbps SuperSpeed+ data rate over 2 lanes using 8b/10b encoding, while USB 3.2 Gen 2×2 combines 2 lanes and 128b/132b encoding to support 20 Gbps SuperSpeed+ data rates.

But a mishmash of often incomplete and/or incorrect terminology, coupled with consumers’ instinctive interpretation that “larger numbers are better”, has severely muddied the waters as to what exactly a consumer is buying and therefore should expect to receive with a USB 3-based product. In fairness, the USB Implementers Forum would have been perfectly happy had its member companies and compatibility certifiers dispensed with the whole numbers-and-suffixes rigamarole and stuck with high-level labels instead (40 Gbps and 80 Gbps are USB4-specific):

That said:

• 5 Gbps = USB 3.0, USB 3.1 Gen 1, and USB 3.2 Gen 1 (with “Gen 1” implying single-lane operation even in the absence of an “x” lane-count qualifier)
• 10 Gbps = USB 3.1 Gen 2, USB 3.2 Gen 2 (with the absence of an “x” lane-count qualifier implying single-lane operation), and USB 3.2 Gen 2×1 (the more precise alternative)
• 20 Gbps = USB 3.2 Gen 2×2 (only supported by USB-C).

So, what, for example, does “10 Gbps USB 3” mean? Is it a single-lane USB 3.1 device, with that one lane capable of 10 Gbps speed? Or is it a dual-lane USB 3.2 device with each lane capable of 5 Gbps speeds? Perhaps obviously, try to connect devices representing both these 10 Gbps implementations together and you’ll end up with…5 Gbps (cue sad trombone sound).

So, like I said, what a mess. And while I’d like to think that USB4 will fix everything, a brief scan of the associated Wikipedia page details leave me highly skeptical. If anything, in contrast, I fear that the situation will end up even worse. Let me know your thoughts in the comments.

 —Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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