USB Cheat Sheet (2022)

A comprehensive guide to understanding the confusing world of USB standards, covering speeds, naming conventions, and power delivery specifications to help users avoid common misunderstandings.

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.

1. Marketing Names and Signal Speeds

| 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 / 3.1 Gen 1 / 3.2 Gen 1 | 5000 Mbps | 625 MiB/s | 8 | 3m | | SuperSpeedPlus USB 10Gbps | USB 3.1 Gen 2 / 3.2 Gen 2 | 10000 Mbps | 1250 MiB/s | 8 | 2m | | SuperSpeedPlus USB 20Gbps | USB 3.2 Gen 2x2 | 20000 Mbps | 2500 MiB/s | 12 | 1m | | USB4 20Gbps | USB4 Gen 2×2 | 20000 Mbps | 2500 MiB/s | 12 | 0.8m | | USB4 40Gbps | USB4 Gen 3×2 | 40000 Mbps | 5000 MiB/s | 12 | 0.8m |

2. Effective Rates and Encoding

USB Gen A x B (A = Generation, B = Num lanes used)

| Name | Signal Total | Encoding | Effective Rate | Real Life (Sequential Read) | |---|---|---|---|---| | USB 3.2 Gen 1x1 | 5,000 Mbps | 8b/10b | 4,000 Mbps | ~400 MiB/s | | USB 3.2 Gen 1x2 | 10,000 Mbps | 8b/10b | 8,000 Mbps | ~800 MiB/s | | USB 3.2 Gen 2x1 | 10,000 Mbps | 128b/132b | 9,696 Mbps | ~780 MiB/s | | USB 3.2 Gen 2x2 | 20,000 Mbps | 128b/132b | 19,392 Mbps | ~1,600 MiB/s | | USB 4 Gen 2x2 | 20,000 Mbps | 128b/132b | 19,392 Mbps | ~1,600 MiB/s | | USB 4 Gen 3x2 | 40,000 Mbps | 128b/132b | 38,787 Mbps | ~2,700 MiB/s |

Note: Multi-lane systems use lane striping (on TX) and lane bonding (on RX).

3. Wire Configuration

4 wires: PWR, GND, D+, D- (1 half-duplex lane).
8 wires: PWR, GND, D+, D-, RX+, RX-, TX-, TX+ (2 lanes: one up, one down).
12 wires: PWR, GND, D+, D-, RX1+, RX1-, RX2-, RX2+, TX1+, TX1-, TX2-, TX2+ (4 lanes: two up, two down).

Only the USB Type-C connector has enough pins to support two lanes. CC1 and CC2 are used for port detection, power negotiation, and alt mode switching.

4. Power Delivery Specifications

| Specifications | Max. Voltage | Max. Current | Max. Power | |---|---|---|---| | USB 2.0 | 5V | 500mA | 2.5W | | USB 3.0 / USB 3.1 | 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 |