USB Reference Guide
A reference for understanding USB standards, speeds, connectors, and power delivery — useful context for getting the most out of USB Connection Information.
USB Versions & Speeds
What are the different USB versions?
| Version | Speed | Name |
|---|---|---|
| USB 1.0 / 1.1 | 1.5 – 12 Mbps | Low Speed / Full Speed |
| USB 2.0 | 480 Mbps | High Speed |
| USB 3.0 / 3.2 Gen 1 | 5 Gbps | SuperSpeed |
| USB 3.1 Gen 2 / 3.2 Gen 2 | 10 Gbps | SuperSpeed+ |
| USB 3.2 Gen 2×2 | 20 Gbps | SuperSpeed+ (dual lane) |
| USB 4.0 Gen 2 | 20 Gbps | — |
| USB 4.0 Gen 3 | 40 Gbps | — |
Note on naming: USB 3.0 was rebranded to USB 3.1 Gen 1, then USB 3.2 Gen 1. The actual speed is what matters — ignore the names where possible.
Why do I see different speeds than advertised?
Several factors affect the negotiated speed:
- Cable quality: Poor cables limit speed regardless of what the port supports.
- Port version: Your computer’s port may be older than the device.
- Device limit: The device itself may not support the faster standard.
- System overhead: Actual throughput is always lower than the theoretical maximum.
USB Connection Information shows the negotiated speed — what the device and port actually agreed on — which reveals exactly where a bottleneck is.
What does “USB 3.1 Gen 1” actually mean?
It’s USB 3.0, renamed. The table below decodes the most confusing equivalences:
| Marketing name | Also called | Speed |
|---|---|---|
| USB 3.0 | USB 3.1 Gen 1 · USB 3.2 Gen 1 | 5 Gbps |
| USB 3.1 Gen 2 | USB 3.2 Gen 2 | 10 Gbps |
| USB 3.2 Gen 2×2 | — | 20 Gbps |
Focus on the speed in Gbps rather than the version name.
Connector Types
USB-A, USB-B, and USB-C
USB-A — the rectangular host connector found on computers, chargers, and hubs. Supports USB 1.0 through USB 3.2. One-way insertion.
USB-B — square with beveled corners, used on printers and scanners. Mostly legacy.
USB-C — small, reversible, oval. Supports USB 3.1, USB 4, and Thunderbolt. Carries data, video, audio, and power over a single cable.
Mini-USB / Micro-USB — older standards. Micro-USB is still common on budget devices and typically limited to USB 2.0 speeds (480 Mbps).
Why is USB-C so confusing?
USB-C is a connector shape, not a speed standard. Two cables that look identical can support completely different capabilities:
| Cable type | Speed | Power |
|---|---|---|
| Cheap USB-C | 480 Mbps (USB 2.0) | 5W |
| Mid-range USB-C | 5–10 Gbps | 18–27W |
| High-end USB-C | 20–40 Gbps | Up to 240W |
| Thunderbolt cable | 40 Gbps | Up to 100W |
USB Connection Information shows what your specific cable and port actually negotiate — removing the guesswork entirely.
Can USB-C carry video?
Yes, via Alternate Modes:
- DisplayPort Alt Mode — up to 8K resolution
- HDMI Alt Mode — less common, up to 4K (often via adapter)
- Thunderbolt — carries DisplayPort signals natively
Not all USB-C ports support video output. Check your device specs or use USB Connection Information to see what’s negotiated.
USB Power Delivery
How does USB Power Delivery work?
USB Power Delivery (USB-PD) enables higher power transfer over USB-C. The charger advertises a list of profiles (voltage + current pairs), and the device picks the most suitable one. This negotiation happens automatically.
| Profile | Power | Typical use |
|---|---|---|
| 5V / 3A | 15W | Standard USB-C |
| 9V / 3A | 27W | Phone fast charging |
| 15V / 3A | 45W | Tablets, small laptops |
| 20V / 3.25A | 65W | Laptops |
| 20V / 5A | 100W | High-power laptops |
| 28V / 5A | 140W | USB PD 3.1 |
What are PD profiles and how do I see them?
A PD profile is a specific voltage/current combination a charger supports. Most chargers support multiple profiles. USB Connection Information reads and displays all profiles advertised by a connected USB-C charger, so you can verify the charger is capable of delivering what your device needs — without a separate USB-C multimeter.
Why is my device charging slowly?
- Wrong cable: Not all USB-C cables support USB-PD high-power charging.
- Wrong charger: The charger may not advertise a profile that matches your device’s fast-charge requirement.
- Port limitations: USB-C ports on hubs and older computers often don’t support high-power output.
USB vs Thunderbolt vs FireWire
USB vs Thunderbolt
| USB 4 Gen 3 | Thunderbolt 3 / 4 | |
|---|---|---|
| Max speed | 40 Gbps | 40 Gbps |
| Minimum guaranteed | 20 Gbps | 40 Gbps (certified) |
| Daisy chaining | No | Yes (up to 6 devices) |
| Connector | USB-C | USB-C |
| Cost | Lower | Higher (strict certification) |
Thunderbolt is a certified superset of USB 4 — guaranteed minimum performance, daisy-chaining support, and stricter manufacturing requirements.
USB vs FireWire
FireWire (IEEE 1394) was Apple’s high-speed standard before USB became dominant.
| USB | FireWire | |
|---|---|---|
| Original speed | 12 Mbps (USB 1.1) | 400 Mbps (FireWire 400) |
| Peak speed | 40 Gbps (USB 4) | 800 Mbps (FireWire 800) |
| Power delivery | Up to 240W (PD 3.1) | Up to 45W |
| Status | Universal standard | Discontinued |
USB won due to lower cost, wider industry support, and continuous evolution. FireWire was technically superior in the early 2000s but couldn’t compete with USB’s ecosystem.
Checking USB on macOS
How do I check USB port speed without the app?
- System Information: Apple menu → About This Mac → System Report → USB
- Terminal:
system_profiler SPUSBDataType - USB Connection Information: Real-time speed in the menu bar — faster and always visible
How do I know if my Mac supports USB 3.0 or higher?
Most Macs from 2012 onwards support USB 3.0. Check System Information for “USB 3.0 Bus”, “USB 3.1 Bus”, etc. USB-C ports on modern Macs support USB 3.1 or higher. USB Connection Information will show you the exact negotiated version for any connected device.