When you buy a USB peripheral, it will specify which the highest standard is that it supports and – sometimes – requires. Which means that some devices simply won’t work properly because they can’t push data through the cable quickly enough. The worst that can happen is that it defaults to the oldest, slowest standard that both devices can understand. In practice this means that if a USB cable fits into a port, it will work. Yet, a key part of USB is the “universal” bit.
The hardware that sends and receives information is faster and the internal wiring differs significantly. That’s because USB standards have improved over the years.
Once it is identified as a high speed device by the controller, the connection is reset and high speed signalling is used.It’s important to understand that although two USB ports and cables might look identical, it doesn’t mean they have the same capabilities. A 2.0 device identifies itself as a full speed device at first then negotiates with the controller via a series of chirps. The 1.0 version can only recognize low speed and full speed devices. USB 2.0 must have backwards compatibility with 1.0 which means that even if you have a 2.0 USB port, you can still stick your USB 1.0 keyboard on it and it would work perfectly. USB 2.0, which is an upgraded version, adds the high speed connection to the previous two standards and results in 480Mbps theoretical throughput. During initialization, a connecting device is identified as low speed device or full speed device. USB 1.0 can either be a low speed device which runs at 1.5mbps or a full speed device at 12Mbps. The very first standard of USB 1.0 provided only 1.5Mbps of speed. Low speed and high speed USB devices and Compatibility But slow speed still remained a hindrance and a trouble. But gradually, the popularity of easy plugging devices and the USB port increased and more devices like digital cameras and camcorders began to switch to USB cable for transferring data by connecting to computer. These devices transmitted only a small amount of data to function. Examples of initial USB are – keyboard, mouse, game controllers etc. The initial version of USB did not support high speed data transmission since it was intended for slower devices. Note that since there are other factors that affect the total throughput, the true speed or the real world speed of both specifications is lower than the specified theoretical maximum. The maximum speed that USB 1.0 devices can achieve is 12Mbps while 2.0 devices can theoretically achieve up to 40 times of that at 480Mbps. USB 2.0 and USB 1.0 differ in the data transfer rate they are capable of.
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