This is by no means a substitute for reading the standard itself. In what follows, some USB 3.x-related terms will be presented briefly and in a shallow manner. The USB 2.0 is relatively well known and documented, and therefore not discussed further. There are no broadcasts to all downstream ports as USB 2.0 hubs do, except for ITP packets, but these are intended for all peripherals. Another related difference is that all packets arriving to a port are intended for that port, even in the presence of USB 3.x hubs along the link.

This doesn't just double the total throughput by allowing both sides to send data at the same time, but improves it significantly by removing the bus turnaround delays and the mechanisms required to prevent both sides from transmitting at the same time (and resolve these situations, should they occur). One major leap forward with USB 3.x is that the communication is full-duplex, unlike USB 2.0, which uses the same pair of wires for communication in both directions.

The raw link data rate on these wires starts at 5 Gb/s in each direction, which is 10 times faster than USB 2.0's 480 Mb/s. This is why special cables and connectors are required for USB 3.x: It's not a matter of higher quality, but more wires in the cable, and connectors that may look the same (in particular the type-A connector) but have in fact additional contacts for these extra 4 (or more) wires. It's yet another variant of the same physical interface used by Gigabit Ethernet, SATA, PCIe, DisplayPort and often in fiber optics. A host can in theory interact with a device through both interfaces in parallel, but it so happens that the USB protocol requires that one should be selected and the other turned off.Īll communication related to the USB 3.x protocol takes place through (at least) 4 dedicated wires, which form a Multi-Gigabit Transceiver (MGT) channel or lane: One pair of differential wires for transmission and one pair for reception. In fact, connecting a standard USB 3.0 device to a host is almost equivalent to connecting two devices, one with a fullblown USB 2.0 protocol stack, and one USB 3.0 device. Even though the USB 3.x standard attempts to present a compatible interface to host's software, it has very little in common with USB 2.0 as far as the low-level communication goes.

Usb 2 vs usb 3 difference