The_JD: U3 is well explained in a google search, specifically http://en.wikipedia.org/wiki/U3

mIRC doesn't have to explain much on its end, the support should be relatively transparent to the user-- though you can always peek through versions.txt for such answers

Code:
36.Added internal U3 support to mIRC. mIRC looks for these command
   line parameters -appStart, -appStop, and -hostCleanUp, and looks
   for U3_HOST_EXEC_PATH and U3_APP_DATA_PATH environment variables.


Again, the user needs not know about these command line switches, as they're used transparently by the U3 device.

- argv[0] on EFnet #mIRC
- "Life is a pointer to an integer without a cast"