When connecting the micro:bit to a computer, it will automatically install a driver to your machine that enables it to communicate as a serial device via USB. There are some cases in which the driver being missing (Windows 7) or a legacy driver being present (Windows 8.1+) could cause an issue with the serial function or with WebUSB.

Windows 7 (serial not working)

In Windows 7, you had to manually install the Mbed serial driver to enable the serial port. The legacy mBed driver is still available, but as Windows 7 reaches end of life you should upgrade your operating system accordingly.

Windows 8.1/10 (WebUSB not working)

If the Mbed Serial driver has been manually installed it might interfere with the Windows 8.1/10 automatic installation of the WebUSB driver. 

It is possible that a driver was previously installed on the Windows machine if you have upgraded from Windows 7

To check if you have this driver already:

  1.  Open Windows Device Manager and see if the micro:bit USB device is shown. If it is...

  2. find the mbed Composite Device entry, right click on it and select Uninstall device.

  3. A new window will open, mark the Delete the driver software for this device box and click Uninstall.

  4. Unplug and replug your micro:bit and it should appear under USB devices.