USB is an industry standard "user-friendly" method of transferring data between a host device (such as a computer) and a peripheral device (such as a mouse). For most computer users, the system can be used by simply connecting various devices through the USB connectors.
USB stands for Universal Serial Bus, and the "bus" in a PC is a collection of wires that transfer data between components inside the computer or between the computer and its peripherals, just as electronic bus bars are central to distributing power in some large, power-hungry environments such as factories and data centers.
Before USB was introduced, each peripheral was connected to a computer with its own uniquely shaped port. As the number of peripheral devices grew over the years, a new standardized method of transferring data between the main host computer and a range of devices was sought. This eventually led to the development of USB.
When a peripheral device is connected via USB, the host computer detects what type of device it is and automatically loads the driver that allows the device to run. Data is transferred between the two devices in small amounts called "packets". Each packet transfers a certain number of bytes.
Interrupted transfers. Peripheral devices such as keyboards and mice use this type of data message to send smaller amounts of data. This type of transmission is typically used for less frequent but important requests. Devices generate requests, but they must wait for the host to ask the remote device for the specific data it needs.
Batch transfer. Printers and digital scanners are used to handle large amounts of data, and this type of transfer is low priority and not time critical. Transfers can be slowed if the host has multiple USB devices connected.
Synchronous transfers. Real-time data such as audio and video is transmitted using synchronous transmission. Errors may occur during the transfer, but the transfer is not interrupted to resend the packet.
Control transfer. This type of data transfer is used to configure and control a USB device. The host sends a request to the device, followed by a data transfer. Control transfers are also used to check status.
USB cables are capable of transferring power and data. To do this, each USB cable has two sets of wires. One set carries the current, while the other carries the data signal.
In a standard USB 2.0 connector, you can see four metal strips. The two outermost strips are the positive and ground wires for the power supply. The two central strips are dedicated to carrying data.
With the newer USB 3.0 connectors, data transfer speeds are increased by adding additional data transfer strips; the four additional signal wires help USB 3.0 achieve its super speed.
USB 2.0 transfers data at a maximum speed of 480 megabits per second (Mbps), while USB 3.0 can transfer data at speeds of up to 5 gigabits per second (Gbps).
You can recognize USB 3.0 connectors by their blue color and the initials SS (for "SuperSpeed").