USB4 Specification
USB is the universal connector. Understanding USB PD for 240W power delivery, USB4 tunneling for Thunderbolt docks, and USB 3.x throughput tiers is essential for hardware-connected software, embedded development, and device driver work.
What It Defines
Defines the Universal Serial Bus protocol stack: physical layer (USB4 v2 = 80 Gbps, USB4 v1 = 40 Gbps, USB 3.2 = up to 20 Gbps), link layer, protocol multiplexing tunnels (PCIe tunneling, DisplayPort alt mode, USB 3.2 tunneling), USB Power Delivery 3.1 (up to 240W via Extended Power Range), and USB Type-C connector with alternate modes. Backward compatible with USB 3.2, USB 2.0, and Thunderbolt 3/4 (Thunderbolt 4 = USB4 with Intel certification). USB-IF maintains class specs for HID, Audio, Mass Storage, CDC, and Video.
Canonical (Normative)
Convenient (Practical)
Related References
Non-profit corporation that manages the USB specification and certification program. Maintains USB4, USB 3.2, USB 2.0, USB Type-C, USB Power Delivery (PD 3.1, up to 240W), and the USB class specifications (HID, Audio, Mass Storage, CDC, Video). USB-IF certification ensures interoperability across billions of devices.
Related Specs
PCIe is the universal high-speed peripheral bus. Understanding lane width, bandwidth, BAR mapping, and MMIO is essential for GPU compute (CUDA/ROCm), NVMe performance tuning, SR-IOV NIC virtualization, and DPDK kernel-bypass networking.