USB stands for Universal Serial Bus. See http://www.usb.org/ for information about USB.Tom Wilkason seems to be successful teaching Tcl to send data through USB ports , as was Uwe Klein, with a SWIGified libusb ...UK the google newslink leads me down a dark alley;-?. I've put a swig of my libusb effort on the net: http://home.foni.net/~kuttersegeln/swig_libusb-20050616.tgz
"Integrating USB into Products" 
AMG: http://www.dlpdesign.com/usb/usb245.shtml is an outstanding product. On my first project using it I had a supremely easy time interfacing it with both the circuit (eight-bit FIFO) and the computer (Tcl opening a MS-Windows COM1:-type device). I highly recommend it.See also Serial Port for an opportunity to access USB via a virtual com port (VCP) driver. -- RJMslebetman Using the VCP driver for the FT245 on Windows I managed to push around 840kb/s from Tcl. The limiting factor appears to be the recieving end which is a small microcontroller with a 5MHz instruction cycle. Tcl's I/O is very fast!APN On Windows, TWAPI's start_device_monitor command can be used for notifications when USB devices are inserted or removed.