Speed.-> USB 2.0 supports a maximum data transmission speed (the rate at which data travels along the bus; also referred to as throughput) of 480Mbps (megabits per second), which is equivalent to 60MBps (megabytes per second). That's more than 300 times faster than the maximum data transmission speeds of a parallel port and more than 4,000 times faster than the top data transmission speeds of a serial port. (USB 1.1 has a much slower throughput than USB 2.0, and we'll discuss this in more detail with the following question.)
Power.-> A single USB interface is capable of carrying 500 milliamps (equivalent to 0.5 amps) of electricity to the various hardware components connected to it. Low-voltage peripherals, including USB hubs and power-efficient storage drives, can use this stream of electricity in lieu of another power source, such as an AC adapter.
Convenience.-> USB technology offers unparalleled convenience for users who need to add hardware to their system. For one thing, each USB port is capable of supporting daisy chains (a string of hardware components connected one to another, just like links on a chain) of as many as 127 devices, so there are virtually no limits to the number of components you can add to a PC. Additionally, the USB ports are hot-pluggable (the ability to recognize and configure a new component without the need to restart the computer), meaning that you can add USB-equipped peripherals to your PC within a matter of minutes, a much quicker and simpler process than in pre-USB days.
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