Universal Serial Bus, or USB is an industry standard cable connecting computers and devices. It is designed to standardize the electric power supply cable for a vast variety of devices.
The USB was developed in the mid 90’s. By now there are three basic formats of USB connectors:
The standard format. This format is designed for desktop or portable equipment such as USB flash drives.
The mini format. A format intended for mobile equipment.
The micro size. This thinner format is designed for low-profile mobile equipment including most modern mobile phones.
Data transfer Modes
There are 5 modes of USB data transfer. In order of increasing bandwidth they include:
Low Speed – USB 1.0 (1996)
Full Speed– USB 1.1 (1998)
High Speed – USB 2.0 (2000)
SuperSpeed – USB 3.0 (2008)
SuperSpeed+ – USB 3.1 (2013)
The various modes have differing hardware and cabling requirements.
USB Port Construction
Different than some other data buses such as Ethernet or HDMI, USB connections are directed, with both upstream and downstream ports emanating from a single host. This applies to electrical power, with only downstream facing ports providing power. This topology was selected for the prevention of electrical overloads and damaged equipment.
USB cables have different ends: A and B, with different physical connectors for each. Generally, each different format requires four different connectors: a plug and receptacle for each of the A and B ends. USB cables have the plugs, with corresponding receptacles on the computers or electronic devices.
The A end is typically the standard format, and the B side varies between standard, mini, and micro. The mini and micro formats also provide for USB On-The-Go with a hermaphroditic AB receptacle, which accepts either an A or a B plug. On-The-Go allows USB between peers without discarding the directed topology by choosing the host when connecting the device.
USB cables are available in various lengths up to 16 feet. That is due to the fact that longer spans are not reliable. They can cause data transfer timing issues and may lead to data loss. However, using a hub for longer spans may help resolve the situation. Connect two USB cables with a hub for a distance longer than 16 feet between devices.