Sunday, February 22


Best Version Number Ever

I learned something new about USB 3.1 today.

The major points to know about this new version of USB are as follows:
  • It runs at 10Gb per second, up from 5Gb for USB 3.0.
  • It supports a new connector, USB type C, which is compact, reversible and the same on both ends of the cable.
  • It supports as much as 100W of power (5A at 20V) so you can charge not just a phone or tablet, but a good-sized notebook.
  • It's backwards-compatible with all the old versions; at most you'll need an adaptor cable.
  • It can carry video signals like DisplayPort for resolutions up to 8K (7680x4320).
The new point is a little less significant, but still nice.  USB 3.0 uses what is known as 8b/10b encoding.  To send 8 bits of data over the bus, you encode it in a 10-bit pattern.  This is a more sophisticated form of the start bit / stop bit / parity on old serial connections.  But it does mean that 20% of the bandwidth is used up by the encoding.

USB 3.1 supports a much longer and hence more efficient pattern - it encodes 128 bits of data in a 132-bit pattern.  That improves efficiency from 80% to 97%.

In effect, USB 3.0 can transfer 500MB of data per second before protocols and error correction.  USB 3.1 can transfer 1200MB per second.

Which makes it fully twice as fast as SATA 3, and offers a much smaller connector than the hideous SATA Express.  Plus one cable carries both data and power.  Plus it's easy to create a USB hub to get more ports. 

I'd like to see internal drives switch entirely over to USB 3.1, with the exception of PCIe x4 M.2 cards with NVMe.

Video is not as cut-and-dried; USB 3.1 can carry a DisplayPort 1.3 signal, which is the highest-speed consumer video standard - but only over a 1 metre cable, which just isn't enough to be practical.  It can carry DisplayPort 1.2 for 2 metres, but that limits you to "only" 4K@60Hz.  So DisplayPort / Thunderbolt cables still have a role there.

DisplayPort 1.3 has been designed to carry USB 3.0 in addition to video, though, so you still get USB everywhere.

Posted by: Pixy Misa at 02:40 PM | No Comments | Add Comment | Trackbacks (Suck)
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