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Not all USB3 ports are created equal.

I have a friend who develops embedded hardware that interfaces with USB chipsets. He told me that most USB chipsets that are slightly faster than USB2 (480 Mbit/s) are labeled as USB3 even if they fall far short of the 5Gb/s theoretical limit.

I'd like to transfer uncompressed video over USB3. According to http://en.wikipedia.org/wiki/Uncompressed_video#Storage_and_Data_Rates_for_Uncompressed_Video 24bit @ 1080i @ 30fps requires 1.39Gbps. How do I measure the actual transfer speed supported by a USB3 port?

Most manufacturers don't mention the actual USB3 speed and I don't have anything to connect to the USB3 port that will transfer at speeds even close to the theoretical speed of 5Gbps. I will later on, when I get the live uncompressed video stream, but I'd like to test the USB3 port before buying this expensive video streaming equipment.

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  • If they don't provide the actual speeds in their specs and you can't convince someone else who owns the hardware to test for you, you can't know in advance (prior to buying the component) the speed. It also depends on the protocol and how much overheard it is and how sensitive to latency it is (low chattiness + low overhead = high throughput). You'll get different overheads for UASP (low or no overhead), UAS (very low overhead), Mass Storage Bulk Only Transport (medium overhead), or a networking protocol like SMB over TCP/IP (very high overhead) or FTP over TCP/IP (high overhead). – allquixotic Mar 15 '13 at 18:06
  • USB3 150-300MB/s(1200-2400Mbit/s) maximum, depending on the controller – STTR Mar 15 '13 at 18:13
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Most tech sites (annandtech, techreport, etc) include USB comparisons in their motherboard reviews. For example techreport in this review uses CystalDiskMark to compare read/write speed of various controllers. They use an external drive to test the USB speed. From the testing methods page:

The Force GT 120GB SSD was used as the system drive for all tests. The Samsung 830 Series 256GB was connected as secondary storage to test Serial ATA and USB performance, the latter through a USAP-compatible Thermaltake BlacX 5G docking station. With RoboBench, we used the Samsung SSD as the source drive and the OCZ RevoDrive 3 X2 240GB as the destination for the read speed tests. Those roles were reversed for RoboBench's write speed tests.

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  • What are they having CrystalDiskMark run against? Perhaps an SSD drive inside a hard-drive enclosure with a USB3 interface? – Gili Mar 15 '13 at 18:42
  • Yes they are using a SSD externally. I updated the answer with info from the testing methods page. – Brad Patton Mar 15 '13 at 18:47
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    While USB has a larger market share, you might want to consider connectivity via Firewire/IEEE 1394 if available. IEEE 1394 is more suitable for isochronous streams (guaranteed bandwidth), is a common standard for A/V equipment, and does not inherently place load on the CPU. See its wiki article for comparison with USB. – Nevin Williams Apr 14 '13 at 8:02

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