The US Robotics 56K Fax Win Int driver refers to the software required for a US Robotics 56K internal fax modem to work on a Windows operating system. This modem typically supports dial-up internet connections as well as sending and receiving faxes. These modems were more commonly used in the late 1990s and early 2000s, but they can still be used for certain applications, especially if you need faxing capabilities over a phone line.