usb

Universal Serial Bus (USB) is an industry standard that specifies the physical interfaces and protocols for connecting, data transferring and powering of hosts, such as personal computers, peripherals, e.g. keyboards and mobile devices, and intermediate hubs. USB was designed to standardize the connection of peripherals to computers, replacing various interfaces such as serial ports, parallel ports, game ports, and ADB ports. It has become commonplace on a wide range of devices, such as keyboards, mice, cameras, printers, scanners, flash drives, smartphones, game consoles, and power banks.
As of 2023, USB consists of four generations of specifications: USB 1.‘‘x’’, USB 2.0, USB 3.‘‘x’’, and USB4. Since USB4 the specification enhances the data transfer and power supply functionality with connection-oriented, tunneling architecture designed to combine multiple protocols onto a single physical interface, so that the total speed and performance of the USB4 Fabric can be dynamically shared. USB4 particularly supports the tunneling of the Thunderbolt 3 protocols, namely PCI Express (PCIe, load/store interface) and DisplayPort. USB4 also adds host-to-host interfaces.Each specification subversion supports different maximum signaling rates from 1.5 Mbit/s in USB 1.0 to 80 Gbit/s in USB4. USB also provides power supply to peripheral devices; the latest versions of the standard extend the power delivery limits for battery charging and devices requiring up to 240 watts (USB Power Delivery (USB-PD)). Over the years USB(-PD) has been adopted as the standard power supply and charging format for many mobile devices, such as mobile phones, reducing the need for proprietary chargers.USB connector interfaces are classified into three types: A (host), B (peripheral), and C (2014, replaces A and B). The A and B types know different sizes: Standard, Mini, and Micro. The standard size is the largest and is mainly used for desktop and larger peripheral equipment. The mini size was introduced for mobile devices, but it was replaced by the thinner micro size. The micro size is nowadays the most common for smartphones and tablets. The USB Type-C connector interface is the newest and the only one applicable to USB4. It is reversible and can support various functionalities and protocols; some are mandatory, many just optional, and depending on the type of the device: host, peripheral device, or hub.Since the USB 1.1 specification fully replaces the USB 1.0 specification, and since the USB 3.2 specification fully replaces the USB 3.1 (and therefore the USB 3.0 specification as well), and since USB 2.0 is backward-compatible with USB 1.0/1.1, and since the USB 3.x specifications include the USB 2.0 specification, and since USB4 "functionally replaces" the USB 3.2 specification "while retaining USB 2.0 bus operating in parallel", backward-compatibility is always given, but obviously always comes along with a decrease in, both, signaling rates and power rates, and less supported functionalities.The USB 3.0 specification defined a new architecture and protocol, named SuperSpeed (aka SuperSpeed USB, marketed as SS), which included a new lane for a new signal coding scheme (8b/10b symbols, 5 Gbps; also known as Gen 1) providing full-duplex data transfers that physically required five additional wires and pins, while preserving the USB 2.0-architectur and -protocols and therefore keeping the original 4 pins/wires for the USB 2.0 backward-compatibility resulting in 9 wires (with 9 or 10 pins at connector interfaces; ID-pin is not wired) in total. The USB 3.1 specification introduced an Enhanced SuperSpeed-architecture – while preserving the SuperSpeed-architecture and -protocol – with an additional SuperSpeedPlus-architecture adding a new coding schema (128b/132b symbols, 10 Gbps; also known as Gen 2) and protocol named SuperSpeedPlus (aka SuperSpeedPlus USB, for some time period marketed as SS+). The USB 3.2 specification even added an additional second lane to the Enhanced SuperSpeed-architecture besides other enhancements, so that SuperSpeedPlus USB implements the Gen 1x2, Gen 2x1 and Gen 2x2 operation modes. The SuperSpeed-architecture and -protocol (aka SuperSpeed USB) still implements the one-lane Gen 1x1 operation mode. Therefore, two-lane operations, namely USB 3.2 Gen 1x2 (10 Gbit/s) and Gen 2x2 (20 Gbit/s), are only possible with Full-Featured USB Type-C fabrics (24 pins). As of 2023, they are hardly yet implemented by most products so far. On the other hand, USB 3.2 Gen 1(x1) (5 Gbit/s) and Gen 2(x1) (10 Gbit/s) implementations are quite common now for some years.

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