I dont think this is possible without changing the firmware on the interface chip (the magic chip) or without somehow disabling that function on your PC USB port.
You could plug in the mbed and then dismount the device again, but it would show up again next time you insert the cable.
If you are looking for a standalone mbed, just power it from an independant source. You could even do that by using a modified USB cable that has disconnected D+ and D- pins.
Obviously, you loose the serial port function also.
In case you still want the serial port connection, but not the USB drive function then you may want to look into the USB CDC libs and use the mbeds separate USB port.
You would only need the normal USB port when downloading a new bin.
Dear friends,
When mbed is connected to PC, a 2MB USB drive is shown up where you can copy .bin files. I want to remove this from mbed. Guess if I burn the mbed with Flash Magic, this USB drive might not show up. But if I want this USB drive back again, what should I do (where can i get the USB program?)?
Thanks