Working with USB 3 and 4 in Windows

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HARDWARE By Ed Tittel The Universal Serial Bus, most commonly known as USB, has been a basic staple of computing since it first arrived on the scene i
[See the full post at: Working with USB 3 and 4 in Windows]

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fisher75, lmacri, SueW, schmootoo, SupremeLaW, abbodi86

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I don’t remember which current “nomenclature” to use with the following;  nevertheless,

I believe a “legacy frame” was chosen for 5G USB and prior versions:  8b/10b = 10 bits per byte

I believe a “jumbo frame” was chosen for 10G USB+:  128b/132b = 132 bits per 16-byte frame

These different frames are relevant factors when estimating “upstream bandwidth”.

Thus, 5G USB 3.0 = 5 GHz / 10 bits per byte  =  500 MB/second MAX HEADROOM.

That latter calculation is the main reason why external HDDs perform just fine with 5G USB 3.0 host ports e.g. one HDD capable of 250MB/s is still using only 50% of available upstream bandwidth.

Similarly, although modern 6G SATA-III SSDs are capable of >550MB/s (measured) , their innate controller overheads should deliver around 450MB/second on a 5G USB 3.0 host port (500 – ~50).

That difference shows up in comparable measurements, but is not large enough to be noticed during routine operations.

Hope this helps.

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Ed Tittel

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Your explanation provides additional insight into the difference between UASP (USB-Attached SCSI Protocol) storage devices and those that simply support USB 3. Indeed, I’ve routinely observed and reported data rates maxing out at around 450 MBps on plain-vanilla USB3 versus data rates from 950 MBps to just over 1000 MBps for UASP. You will often observe a “jump” in speed for a UASP device, in fact, when moving it from a USB 3.x port to a higher-speed USB-C port because that allows the device to “go faster.”

Thanks again,

–Ed–

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SupremeLaW

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Logitech has said their usb receivers should be plugged into usb 2.0 ports because usb 3.0 can cause interference with the 2.4ghz signal. I’ve seen this happen myself when I plugged a tranceiver directly into one of the 3.2 ports on the back of the motherboard. Using a USB extension cord, hub, or ports not directly on the motherboard also alleviates this interference problem.

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Ed Tittel, Steve79, SupremeLaW

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