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May 05, 2022
USB Cheat Sheet

I spend time investigating a non-existing bug today because I misunderstood a USB term. So I made myself a cheat sheet. Maybe it will save time to someone.

Marketing Name Also Known As Signal Gbps Signal MiB/s Wires Cable
USB 1.1 Full Speed 12 Mbps 1.5 MiB/s 4 4m
USB 2.0 Hi-Speed 480 Mbps 60 MiB/s 4 4m
SuperSpeed USB  5Gbps USB 3.0
USB 3.1
USB 3.2
USB 3.1 Gen 1
USB 3.2 Gen 1
 5000 Mbps 625 MiB/s 8 3m
SuperSpeedPlus USB 10Gbps USB 3.1
USB 3.2
USB 3.1 Gen 2
USB 3.2 Gen 2
 10000 Mbps 1250 MiB/s 8 2m
SuperSpeedPlus USB 20Gbps USB 3.2
USB 3.2 Gen 2x2
 20000 Mbps 2500 MiB/s 12 1m
USB4 20Gbps USB4 Gen 2×2
USB4
 20000 Mbps 2500 MiB/s 12 0.8m
USB4 40Gbps USB4 Gen 3×2
USB4
 40000 Mbps 5000 MiB/s 12 0.8m

Gen naming Convention, lanes, and Speed

USB Gen A x B
A = Generation
B = Num lanes used

Name Signal Sig Totala Encoding Effective bb Effective Bb Real Lifec
USB 3.2 Gen 1x1 5,000 Mbps 5,000 Mbps 8b/10b 4,000 Mbps 500 MiB/s 400 MiB/s[1]
USB 3.2 Gen 1x2 5,000 Mbps 10,000 Mbps 8b/10b 8,000 Mbps 1,000 MiB/s 800 MiB/s  
USB 3.2 Gen 2x1 10,000 Mbps 10,000 Mbps 128b/132b 9,696 Mbps 1,212 MiB/s 780 MiB/s[2]
USB 3.2 Gen 2x2 10,000 Mbps 20,000 Mbps 128b/132b 19,392 Mbps 2,424 MiB/s 1,600 MiB/s[4]
USB 4 Gen 2x2 10,000 Mbps 20,000 Mbps 128b/132b 19,392 Mbps 2,424 MiB/s 1,600 MiB/s  
USB 4 Gen 3x2 20,000 Mbps 40,000 Mbps 128b/132b 38,787 Mbps 4,848 MiB/s 2,700 MiB/s[5]

Note: Multi-lanes systems, uses lane striping (on TX) and lane bonding (on RX).
a - What they put on the box.
b - Rate with encoding overhead. e.g, 8b/10b = 20%.
c - Real life sequencial read rate.

Cables

 4 wires: PWR, GND, D+, D-.
 8 wires: PWR, GND, D+, D-. RX+ , RX- , TX- , TX+.
12 wires: PWR, GND, D+, D-, RX1+, RX1-, RX2-, RX2+, TX1+, TX1-, TX2-, TX2+.

Note: 1 USB lane = 1 twisted wire pair +/-.
Note: 4 wires = 1 half-duplex lane, 8 wires = 2 lanes (one up, one down), and 12 wires = 4 lanes (two up, two down).

USB-A/B: Connectors 4/8 wires

Type-A 4-wires Type-A 8-wires Type-B 4-wires Type-B 8-wires

USB-C: Connectors 12 wires

Only the USB Type-C connector has enough pins to support two lanes.

- CC1 and CC2 are downstream facing port (DFP) and upstream facing port (UFP) detection. Also used for power negotiation and alt mode switch.
- SBU1 and SBU2 are secondary bus wires, for the DisplayPort AUX channel and hot plug detection (HPD).

Charge rates / Cable types

Specifications Max. Voltage Max. Current Max. Power
USB 2.0 5V 500mA 2.5W
USB 3.0 / USB3.1 5V 900mA 4.5W
USB Battery Charging (BC) 1.2 5V 1.5A 7.5W
USB-C Current Mode (non-PD) 5V 3A 15W
USB-C / Power Delivery (PD 1/2) 20V 5A 100W
USB-C PD 3.1 (EPR) 48V 5A 240W

Specifications

USB 1.0 (Jan, 1996).
USB 1.1 (Sep, 1998).
USB 2.0 (Apr, 2000).
USB 3.0 (Nov, 2008).
USB 3.1 (Jul, 2013).
USB 3.2 (Sep, 2017).
USB 4.0 (Aug, 2019).

References

^ [1]Universal Serial Bus Revision 3.0 Specification
^ [2]Real-world USB 3.2 Gen 2 Performance
^ [3]USB 3.1 Tested: Performance
^ [4]World’s First USB 3.2 Demonstration | Synopsys
^ [5]USB4.0 M.2 NVMe Enclosure Review

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