USB 2.0 is the Universal Serial Bus (USB) standard. Nearly all USB-capable devices and nearly all USB cables support at least USB 2.0 (often referred to as Hi-Speed USB ).
Devices that comply with this USB standard are capable of transferring data at speeds up to 480 Mbps. This is faster than the old USB 1.1 standard, but much slower than the new USB4 standard.
USB 1.1 was released in August 1998, USB 2.0 was released in April 2000, USB 3.0 was released in November 2008, and USB4 was released in August 2019.
Plug is the name for the male connector on a USB 2.0 cable or flash drive, while socket is the name for the female connector on a USB 2.0 device or extension cable.
- USB Type A: Technically called USB 2.0 Standard-A, these connectors are the perfectly rectangular USB connectors found on most non-mobile devices. The USB 2.0 Type A connector is physically compatible with USB 3.0 and USB 1.1 connectors.
- USB Type B: Technically called USB 2.0 Standard B, these connectors are square in shape except for a small notch at the top. The USB 2.0 Type B plug is physically compatible with USB 3.0 and USB 1.1 Type B receptacles, but the USB 3.0 Type B plug is not backwards compatible with the USB 2.0 Type B receptacle.
- USB Micro-A : These connectors, especially the plug, look like a miniature version of the USB 2.0 Type A connector. The USB 2.0 Micro-A plug is compatible with USB 2.0 Micro-AB receptacles and USB 3.0 Micro-AB receptacles. However, the newer USB 3.0 Micro-A plug does not fit into the USB 2.0 Micro-AB socket.
- USB Micro-B : These connectors are small and rectangular, but two corners on one side are angled rather than square. The USB 2.0 Micro-B plug is compatible with four types of sockets: USB 2.0 and USB 3.0 Micro-B and Micro-AB sockets. Newer USB 3.0 Micro-B plugs are not backwards compatible with USB 2.0 Micro sockets.
- USB Mini-A : These connectors are small, mostly rectangular, and very rounded on one side. USB 2.0 Mini-A plugs are only compatible with USB 2.0 Mini-AB sockets.
- USB Mini-B : These connectors are small, mostly rectangular, with noticeable indentations on the short sides. The USB 2.0 Mini-B plug is compatible with USB 2.0 Mini-B and USB 2.0 Mini-AB receptacles.
Only USB 2.0 supports USB Mini-A, USB Mini-B, and USB Mini-AB connectors.
You may want to consult the USB physical compatibility table for reference on what is suitable for what.
Older USB 1.1 devices and cables are mostly physically compatible with USB 2.0 hardware. However, the only way to achieve USB 2.0 transfer speeds is if all interconnected devices and cables support USB 2.0.
For example, if you have a USB 2.0 device used with a USB 1.0 cable, the 1.0 speed will be used regardless of whether the device supports USB 2.0 because the cable does not support newer, faster speeds.
USB 2.0 devices and cables used with USB 3.0 devices and cables (assuming they are physically compatible) will operate at lower USB 2.0 speeds.
In other words, the transfer speed drops to the older of the two technologies. This makes sense, since you can't get USB 3.0 speeds from a USB 2.0 cable, nor can you get USB 2.0 transfer speeds with a USB 1.1 cable.
USB On-the-Go was released in December 2006. It allows devices to switch between master and slave when necessary so that they can connect directly to each other.
For example, a USB 2.0 smartphone or tablet might be able to act as a host to extract data from a flash drive, then switch to slave mode when connected to a computer to obtain information from it.
The device that provides power (the host) is considered an OTG A device, while the device that consumes power (the slave device) is called a B device. In this type of setup, the slave device acts as a peripheral device.
Role switching is performed using the Host Negotiation Protocol (HNP), but physically choosing which USB 2.0 device should be considered a slave or host by default is as simple as choosing which end of the cable the device is connected to.
Occasionally, the master will do an HNP poll to determine if the subordinate has requested to become the master, in which case they can swap places. USB 3.0 also uses HNP polling, but it is called Role Switching Protocol (RSP).
