USB LIMITATIONS

USB (Universal Serial Bus) is a serial bus standard to connect devices to your computer. As you may already know the USB specification limits the length of a cable between high speed devices to 5 meters (about 16 feet) and for low speed devices the limit is 3 meters (about 9 feet).

The primary reason for this limit is the maximum allowed round-trip delay. If USB host commands are unanswered by the USB device within the allowed time, the host considers the command lost. So in order to meet the USB specification, cable length should be not longer than 5 or 3 meters as described above.

 

The limitations one may face while using USB cable:

1. Each USB cable can't be longer than 5 meters.

16 feet (5 m) is the farthest USB cables signal can go without running into timing problems. This is built into the USB Specification, and can't be changed. And of course it is impossible to bypass this limit by connecting several USB cables to make a long one and plug in a USB device that is so far away from your host PC.

2. Each USB device can't have more than 5 "nodes" between it and the PC.

A "node" is a hub, switch, or repeater, allowing another set of devices to be attached to the USB network. You can't plug a scanner into your computer via 6 hubs, because that's six "nodes" between your scanner and the PC. There's not enough space in the addressing scheme for the computer to send or receive data from the scanner to the computer. This rule cannot be disobeyed.

3. Not all virtual machines can work with USB devices.

It is frequently needed to use USB devices at virtual machines, but impossible to connect USB device to some of them.

The Universal Serial Bus allows connecting up to 127 devices to a computer.

Did you know?

In order to go beyond these limits you need to use USB hubs, USB active extension cables or USB over Network products.



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