Quick-reference guide to USB connector types, speed tiers from USB 2.0 through USB4, Thunderbolt overlap, and Power Delivery profiles.
Key Takeaways
USB 3.0, USB 3.1 Gen 1, and USB 3.2 Gen 1 all refer to the same 5Gbps spec – three names, one speed.
USB 3.2 Gen 2x2 hits 20Gbps by bonding two 10Gbps lanes over Type-C; Gen 2x1 is 10Gbps on a single lane.
USB4 adopts speed-first naming (USB4 40Gbps, USB4 80Gbps) and is derived from the Thunderbolt 3 spec.
Type-C SBU pins carry sideband data – UART on some devices, audio on others – not a secondary bus.
Thunderbolt 3+ is physically USB-C but adds mandatory PCIe tunneling, DisplayPort, and a guaranteed 40Gbps floor.
Hacker News Comment Review
Strong consensus that USB 3.x naming is intentional obfuscation: vendors re-badge older stock under current-sounding labels, and USB-IF accommodates it; USB4’s speed-first naming is seen as a belated fix.
MacBooks expose a real-world gap: Apple supports USB4/Thunderbolt 4 and 5 but omits USB 3.2 Gen 2x2, so cheaper 20Gbps drives are silently capped at 10Gbps on those machines.
Commenters flag gaps in the cheat sheet: female/male crossover pinout for Type-C, Power Delivery generations and profiles, and USB4v2’s PAM3 11b/7t signaling scheme are all missing.
Notable Comments
@DHowett: corrects SBU to “Sideband Use” (not “Secondary Bus”) citing the USB 3.0 Promoter Group spec PDF directly.
@maxloh: proposes the cleaner alternative – “USB 3 5Gbps / 10Gbps / 20Gbps” – and argues the current layering exists so vendors can sell old stock as current-generation hardware.
@retired: concise Thunderbolt counterexample – TB1=10G, TB2=20G, TB3=40G, TB4=40G, TB5=80/120G – with every cable carrying DisplayPort 2.1, PCIe, USB4, and up to 240W PD.
