USB Info & Tips

(For Geeks Only)
By Joe Callison
17 March 2018

USB or Universal Serial Bus started showing up in computers in 1998, beginning with the Apple iMac. The USB 1.1 ports were designed for Low Speed (1.5 mbps) or Full Speed (12 mbps). Three years later the USB 2.0 standard improved USB to High Speed (480 mbps) and supported up to 100mA (0.5W) of power for low power and up to 500mA (2.5W) for high power. SuperSpeed USB 3.0 devices started showing up in 2010. The first generation USB 3.1 supports 5 gbps speed and up to 150mA (0.75W) for low power or up to 900mA (4.5W) for high power. The second generation of USB 3.1 increased the top speed to 10 gbps, and the current USB 3.2 top speed is 20 gbps. The USB 3.x standards are backward compatible to USB 2.0 devices.  

The USB-C port and cable design implements the USB 3.x standards for data, but can provide or consume up to either 1.5A or 3.0A of additional power for other uses such as powering peripherals or recharging the computer. The USB-C port and cable designs have a minimum rating of 3A (60W) @ 20V, up to a maximum rating of 5A, 100W. It can also incorporate additional signals such as audio, or other signals in proprietary designs.

A computer with multiple USB ports usually has shared ports, that is, multiple shared USB ports connected to one USB host controller. The available power and data bandwidth is shared among the ports. There may be multiple USB host controllers, each with 2 to 4 shared ports. For example, one host controller may serve 4 ports on the rear of the computer and one host controller may serve 2 ports on the front of the computer. Many new computers are provide with up to 6 USB 2.0 ports and 2 USB 3.x ports. Some have an additional USB-C port.

If more USB ports are needed than are available on the computer, an external USB hub may be used. Unpowered USB hubs have capability issues with devices that need more power to operate than the USB port of the computer can supply to the hub. A low power USB 2.0 port can supply up to 100mA of current, which may also be shared with other ports on the computer. If an unpowered 4 port hub is attached to the port, the 100mA of current is then also shared by the additional 4 ports of the hub. A powered USB 2.0 hub uses an ac to dc power adapter to power the ports of the hub, and may supply 100mA, or even up to 500mA of current for each of the 4 ports on the hub.

Another solution for increasing the number of USB ports may be to install an accessory card in an available slot in the computer. This can also allow you to upgrade to a newer USB standard. USB cards typically have 2 to 4 ports for external connection and may have additional ports or USB headers internally.

Older motherboards with PS/2 type ports for the mouse and keyboard are often used with a newer USB mouse and keyboard attached. The mouse and keyboard are typically not recognized by the computer until late in the boot process or even after the operating system is fully loaded. This could prevent being able to get into the BIOS settings or safe mode. There is often a selection in BIOS for Legacy Support, which enables the BIOS to trap events from the USB keyboard and mouse and present them to the system as PS/2 compatible devices. Of course, a PS/2 mouse and keyboard would have to be temporarily used to enter BIOS to make the selection. Legacy Support is also required if you want to use DOS or other operating systems that do not support USB.

Most of us are aware that we should not disconnect a USB flash drive or external hard drive while it is accessing its memory, and it is best to eject the device either from the icon in the tray of the taskbar or through menu selection in File Explorer before disconnecting. Ejecting stops the device and shuts off the power to it. If you forget and the disconnected device is made unreadable or corrupted, it is possible to select the drive in File Explorer, choose Properties, Tools, and run the error checking to attempt to repair it.

If your computer stops recognizing an attached USB device, first try unplugging the USB connection, wait a few seconds, and plug it back in. If still not recognized, try plugging it into a different USB port, swapping locations with another device if you need to. If still no luck then go to Device Manager and Scan for Hardware Changes. If it still does not work then restart the computer and see if that clears it up. If not, then go back to Device Manager and under Universal Serial Bus Controllers, find and uninstall any listed controllers, and then restart the computer. Failure at this point may necessitate checking that the device still works by plugging it into another computer before bothering with any more troubleshooting methods.

Posted by Joe Callison

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